Popular Scientific Recreations / in Natural Philosphy, Astronomy, Geology, Chemistry, etc., etc., etc.

by Gaston Tissandier

CHAPTER XLV.

THE MESOZOIC SYSTEM—THE TRIASSIC, OOLITIC, AND CRETACEOUS FORMATIONS—THE EOCENE, MIOCENE, AND PLIOCENE—THE GLACIAL PERIOD—PRE-HISTORIC MAN.

We trust that the general reader has gleaned from the foregoing chapter some few ideas concerning the growth of plant and animal life in the early periods of the world’s existence. From the Laurentian System we have briefly traced the conformation of the globe at the dawn of organic life through the Silurian Old Red Sandstone and Carboniferous formations, indicating as we proceeded the chief points in the world’s history, and the gradual development of life through many ages. There is no real or bold line of demarcation drawn between these systems. As seam unites to seam, and layer to layer, stratum upon stratum, so the systems almost insensibly unite, and forms of life appear, mature, and die away as the babe grows into the man, and dies away again to old age and final extinction. So one system merges into another, each and all a factor in the great work which was intended to prepare the earth for the greatest and latest development of Nature—Man!

Fig. 670.—Fossils of the Trias Group.
1. Ammonites nodosus. 3. Possidonia minuta.
2. Avicula socialis. 4. Encrinites moniliformis.

But all this while the earth had been, as it still is, undergoing continual change. Sometimes gradually, in the wearing away, or elevation of beach or headland; sometimes suddenly, as when mighty hills were upheaved and the deeply-laid granite or limestone was lifted to the summits of the mountains from the depths of the sea. Land and water came and went, and the ever-changing earth still brought forth abundantly “the herb yielding seed after its kind,” and the “moving things upon the ground after their kind,” ever improving and developing till they culminated in the splendid vegetation and immense animals of the Tertiary period, and lay silent afterwards in the cold grasp of the great ice age for the thousands of years of the glacial epoch.

Fig. 671.—Plesiosaurus.

We now enter upon the Trias, or New (Upper) Red Sandstone, which is divided into Upper and Lower Trias, “Keuper” and “Bunter.” We have three principal headings in the Secondary System—the Triassic (the oldest), the Oolitic, and the Cretaceous. In the first we find red sandstones and shelly limestone; in the second, clays and shale; in the last, chalk, or white limestone. In some districts there are traces of volcanic action.

Fig. 672.—Restorations of Saurians, etc.

On the top of the “Upper Trias,” or “Keuper” formation, we have the Lias, which succeeds the Rhætic beds, and in this we find many rich traces of reptiles and birds which come now before us in the rising scale of creation. In the seas of this period we have numerous crustacea, the nautilus and the cuttle-fish. The Saurians now come before our retrospective vision. It is the “Reptile Age” in all its development, and the huge labyrinthodon, the iguanodon, pterodactyle, and ichthyosaurus testify to the magnitude of the fauna of the period. The first mammal specimen, a marsupial, has been traced back to this time; and the tropical temperature was favourable for luxuriant vegetation, pines, and palms.

In the swamps or shallow waters the great reptiles disported themselves, and seized their prey, the water-fowl, which now appeared in numbers, and of enormous size. Nor were insects absent. Numbers of remains have been discovered; beetles, dragon-flies, grasshoppers, etc., in multitudes yield us information, while the marine fossils, star-fish, mollusca, and various fishes, are of frequent occurrence. Animal and vegetable life during this period must have been very rich and varied—literally leaving “footprints in the sands of time.”

Fig. 673.—Pterodactylus longirostris.

The “Blue Lias” is a term familiar to every reader. It is a kind of limestone mixed with clay, of a blue colour, and upon this we find the Oolitic, or Oolite System—so called because it somewhat resembles the roe of a fish. The Lias clays are used for bricks, and Whitby “jet” is also obtained from the Upper Lias. Jet is really a lignite, or wood in the process of transmutation. In this Lias formation, besides the numerous fossil remains already mentioned, we find the “snakestones” (ammonites), the stone-lily, and belemnites, with many nautili and shells.

Fig. 674.—Ichthyosaurus.

The Oolite, or Jurassic, underlies the chalk, and overlies the Trias formation. The term “Jurassic” originates from the Jura range, which is almost entirely composed of Oolitic strata. These strata are greatly distorted by pressure, and when we reach Switzerland and the familiar Alps, we find gneiss, crystalline, limestones, and schists, into which the Oolite has been metamorphosed. The Oolite is divided into Upper, Middle, and Lower, consisting of the following:—

Upper Oolite	⌈Pembroke Beds. ⎢Portland Beds. ⌊Kimmeridge Clay.
Middle Oolite	⌈Calcareous Grit. ⎢Coral Rag. ⌊Oxford Clay.
Lower Oolite	⌈“Cornbrash”—Forest Marble. ⎢Stansfield Slate. ⎢Bath Oolite. ⎢Fuller’s Earth. ⌊Inferior Oolite.

Fig. 675.—Sketch-map of various geological formations.

The Oolite formation (see Map) occupies a stretch of country in England extending from Yorkshire into Dorset. The Great Oolite holds the Fuller’s earth, and the Bath stone is also well known. The Stonesfield slate holds many remains of reptiles. It is a kind of shelly limestone, and is used for roofing purposes. The Forest Marble (so called from Wychwood Forest) is a sandy limestone holding marine fossils. It is used for ornaments. The Coral Rag and Oxford clay are rich in fossils, and the former, as its name implies, is composed of ancient coral reef. The Portland beds produce the well-known building stone. The Purbecks, of which there are three divisions, appear to have been deposited in fresh water, and occur in Dorsetshire.

All the Oolite strata supply organic remains. We have plants and ferns, reptiles, and a number of new genera of conchifera and cephalopods, star-fish, urchins, and the enormous bats, and the terrible megalosaurus, and the cetiosaurus, steneosaurus, and pliosaurus, of enormous size. One very remarkable bird has been found in the Bavarian limestone of this period; it is called the Archæopteryx, which is described as having a leg-bone and foot like the familiar birds, but the tail is lizard-like, with feathers springing from each joint. Sponges, corals, and fish, and many other forms of animal life are found in the Oolites. The reptiles must have had it all their own way in this period, for there were both carnivorous and vegetable feeders, and teeth of the pliosaurus have been found which measure fifteen inches, the jaws being six feet long. We have seen that corals must have built up their reefs in the waters, which then overlaid the land we call the United Kingdom.

There must have been great changes during this period, and the strata are chiefly marine. The Wealden formations are the exceptions, and in the fresh-water deposits insect forms abound. The appearance and variety of animal and vegetable life must have been curious and interesting.

The Weald or “Wold” of Kent is often spoken of, and it extends with the Surrey and Sussex Wealden formations for some distance. The strata are of fresh-water deposition, differing in this from the chalk, although the Wealden beds are included in the Cretaceous Group, which is composed as follows:—

Lower	⌈Wealden. ⎢Greensand. ⌊“Gault.”
Upper	⌈Upper Greensand. ⎢Chalk Marl. ⎢Chalk (without Flint). ⎢Chalk (with Flint). ⌊Maestricht.

The “Wealden” formation is divided into Hastings sand and Weald clay. The former consists of clay and sandy beds, and is observable at Hastings, and in the neighbourhood of Tunbridge. The Weald clay consists of blue and brown clays, with sandstone, and the limestone known as “Sussex Marble,” which is formed by the paludina of the rivers. There is another division often seen in Dorsetshire, and called the Punfield beds, which partake both of marine and fresh-water remains, which are distinct in the true Wealden and cretaceous formations, the former being of fresh, and the latter of salt-water origin.

Fig. 676.—Echinus (Hemicidarus intermedia, Chalk).

The remains of enormous reptiles are numerous in the Wealden formations; crocodiles, lizards, turtles of gigantic size have been discovered, and most curious fossils have been disinterred in the Hastings district. The “Greensands” are separated by what is termed gault, a stiff blue clay found in Norfolk, Essex, and Kent. The Lower Greensand includes the well-known Kentish rag, or limestone, of which so many churches are built. The Upper Greensand is supposed to be a seashore deposit on the sides of an extensive ocean or sea, at the bottom of which the chalk was formed. After the Wealden beds were formed, they were covered by these greensand estuary-beds, or littoral strata. In these series new forms of life appeared, and the waters became the receptacle of myriads of mollusca, etc., which in time formed the great chalk cliffs and downs so often referred to. The chalk is interstratified with sand, which as “gault” and “greensand” was probably the sand of the ocean bed before the chalk was formed upon it, and the seas must have supported many marine reptiles, for stony “nodules,” or coprolites, which are the fossil excreta of the animals, are found, and now used for manure, after being buried for thousands of years. Examination of these remains has resulted in the discovery of the teeth and bones of fish which had been devoured by the gigantic reptiles. An illustration of a shell thus discovered is annexed.

Fig. 677.—Nautilus Inequalis.

Fig. 678.—Ammonite from the chalk.

We have in a former chapter spoken of the chalk and its formation. We know that it is composed of the minute foraminifera. The fossil remains are very numerous in chalk and all of a marine kind, such as the ammonites, belemnites, and such cephalopods, and the echinus, bivalve mollusca, crustacea, etc. We have occasionally flints appearing in the chalk, and this circumstance has given rise to some speculation as to how the flints got there, for they consist of nearly pure silica; and the theory of the petrifaction of sponges, madrepores, etc., has been started to account for their presence. Dr. Carpenter says: “It may be stated, as a fact beyond all question, that nodular flint and other analogous concretions (such as agates) may generally be considered as fossilised sponges or alcyonian zoophytes, since not only are their external forms and their superficial markings often highly characteristic of those organisms, but when sections of them are made sufficiently thin to be transparent, a spongy texture may be most distinctly recognised in their interior.”

It is now generally admitted that the decaying animal matter acts upon the silicious spiculæ of sponges, etc., and the silica is thus deposited.

We may then surmise that at some very distant period the whole extent of the British Isles was submerged, as well as portions of the continent, and after the strata had been deposited the sea and land were disturbed by volcanic action. While the secondary strata were being deposited, very little relative alteration took place, as the deposits are seen to lie “conformably.” But when the great convulsion which upheaved the Apennines occurred, the chalk was raised as we find it in the cliffs and downs, which were the beds of seas. This is the last of the great convulsions which the earth has undergone, for the tertiary strata, which afterwards began to be deposited, rest in the hollows or basins (chiefly in the chalk) then left; the alterations in and since these deposits appear to consist chiefly of the upheaval of certain localities, the depression of others, the evaporation of inland lakes, and the wear and tear of the land from these causes, which are still in continuous action (as from the washing down of cliffs by the sea, and the formation of mud deposits at the mouths of rivers), or the volcanic agencies which in some places (as in Ireland) have cast up basalt over the chalk.

Fig. 679.—Mosasaurus (Maestricht).

There is a sort of transition formation which is classed with the Cretaceous System, and termed “Maestricht,” after the town in Belgium. It appears that this is an upper chalk layer, an intermediary between the Secondary and Tertiary, and here on the banks of the Meuse we find the Mosasaurus, the “lizard of the Meuse,” of whose remains we give specimens in the illustration. This transition chalk—as we may call it to distinguish it—must have been laid down at a later period than the flinty chalk, and we find it in many places. It serves therefore as a fitting introduction to the Tertiary Period of Geological time.

The Tertiary Period.

We now enter upon a period when the animal creation attained its greatest development, the “Age of Mammals”; for they were then the kings of creation. The Tertiary Period is divided into three stages, viz.—

The Eocene, or the Dawning of the now existing creation.

The Miocene, or the Middle, or “minority” of existing creation.

The Pliocene, or the Recent, or still more developed period.

We will glance at them in that order, which Sir C. Lyell introduced.

Fig. 680.—Skull of the Dinotherium.

The Eocene formation is shown in what is termed the “London Basin,” here illustrated by a section in which we find soft sands without fossils (Thanet Beds), and a kindred kind in Surrey, in which fossils (marine) are found. After these we get the “Reading and Woolwich” beds as we ascend. These are of clay and pebbles, etc., with river fossils. The Oldhaven beds are included on the map; they occur towards Blackheath and Herne Bay. The London clay is very stiff, and in some places blue. It is full of fossils of birds, beasts, fruits, and vegetables, trees, reptiles, and fish, and the variety of the organic remains appears to indicate the fact that at one time the Thames flowed through swampy ground to the sea, in which dwelt, in a warm climate, immense mammalia, such as the megatherium, glyptodon, tapir, etc., and some turtles of enormous size.

It is also on record from late observations that these immense animals were even mixed up, and almost fabulous creatures inhabited the land where England now is. We read of antelope-horses, lion-like bears, and camel-stags. The vegetation was then of a tropical kind, and in the deep forests and jungles these enormous animals—the mammoth dinotherium, and such species—roamed and plunged in the swamps at the mouth of the Thames. At length these types died away, and gave place to the elephant and the hippopotamus, and the climate by degrees became less warm, and still slowly decreased in temperature.

A glance at Sir C. Lyell’s “Principles of Geology” will show us how, as we examine the more modern strata, we find a great increase in the European lands, which may have been compensated by the submersion of the Pacific islands. During the period of the vegetation of the Secondary epochs, our climate (between the lias and the chalk) was favourable to a tropical growth. Enormous rivers flowed through our islands, and gigantic crocodiles, etc., with flying reptiles, were masters of the land. There were numerous fishes, but the reptiles did not appear in such very great numbers.

Fig. 681.—Section across the London Basin (W. Whitaker).

a Lower Bagshot sand (of Hampstead). b London Clay. c Reading and Woolwich beds (including the Oldhaven beds, which occur in the south only). d Thanet sand (crops out on the south only). e Chalk with flints. f Chalk without flints. g Upper Greensand (crops out on the south only). h Gault. i Lower Greensand. k Wealden beds (on the south only). l Oolitic clays (shown only on the north, but proved to occur on the south beyond the range of the section, by the sub-Wealden boring, near Battle, in Sussex). x Old rocks, shown by borings at Kentish Town and at Meux’s Brewery, to pass under the London basin.

These large and elephantine animals must have existed while the climate of Northern Europe underwent some very considerable changes. We read of the woolly rhinoceros, and the hairy elephant, or mastodon, which has been found in Siberia. Reindeer appeared in England, and we know now that these animals inhabit cold countries. The mountains were considerably elevated during the latter Tertiary period; snow fell and ice formed upon the summits of the mountains, while glaciers crept down the sides. The warm, almost tropical climate of the prior ages was gradually but surely giving way to the Ice Age; the earth was slowly dipping, and the sun’s rays had less power.

Professor Ramsay says the “assemblage of fossils found in the London clay point to the fact that the whole of these strata were deposited in the estuary of a great continental river comparable to the Amazon and the Ganges. The palm-nuts and the host of other plants help to prove it, and the remains of river tortoises, crocodiles, snakes, marsupials, and several tapir-like mammals, all point in the same direction. The estuarine conditions begun during the deposit of the Woolwich and Reading beds were still going on when the London clay was thrown down; with this difference, that by sinking of the area the estuary had become longer, wider, and deeper, but still remained connected with a vast continent, through which the Eocene river flowed.”

Fig. 682.—Anoplotherium commune: palæotherium magnum and minus; and crocodile.

The Miocene deposits are not so generally important in the United Kingdom, but in America very valuable fossils have been discovered in these strata. The Pliocene strata extend along the east of Great Britain, where they are denominated “Crag,” as Norfolk Crag, Red Crag, Coralline Crag. Underneath these mammalian remains have been discovered. After the Pliocene we come to the Post-Pliocene, which really closes the long Tertiary period. During these ages the gradual development of created beings apparently reached its height. It was towards the end of the Middle Eocene that the great mountain chain of Europe came into existence, which is connected, as any casual observer may see, with the Himalaya. In fact, the whole chain, from the Thibetian range through India, the Caucasus, Alps, and Pyrenees, is continuous, and formed of the same material (“nummulitic limestone”). There is no doubt that the whole northern hemisphere enjoyed at the commencement of the Tertiary period a warm, not to say tropical, climate, which got colder and colder.

We find the increase of animals and plants more fitted to the requirements of man and our present climate. There are many signs of the successive increase of land in Europe generally, while the contrast the Tertiary period bears to the Secondary is very marked. In the former we have extensive deposits in the waters of wide, open seas; in the latter the depositions were evidently made where dry land, with its accompanying bays and lakes, were extensive and numerous. The former is marine, the latter lacustrine and marine. The seas of the Tertiary period have lately been defined.

Fig. 683.—Megatherium cuvieri (post-Pliocene), S. America.

Sir Charles Lyell, in his “Principles of Geology,” shows us this, and defines the European features at the commencement of the Tertiary epoch. At that time, the British islands, with the exception of the basins of London, the Isle of Wight, and Norfolk, had wholly emerged from the deep. But a third part of France was still under water. Italy consisted only of a long and narrow ridgy peninsula, branching off from the Alps near Savona. Turkey and Greece, south of the Danube, were laid dry; and a tract of land extended from the Vosges, through central Germany, Bohemia, and the north of Hungary, perhaps to the Balkan. But the whole of the north of Europe and Asia, from Holland eastward to central Tartary, and from Saxony and the Carpathians northward to Sweden, Lapland, and the Ural chain, lay beneath the ocean. The same subterranean movements, which have subsequently raised the wide plains of our northern continents above the sea-level, have given great additional elevation to the then existing land. Thus the Alps have certainly acquired an increased height of from two thousand to four thousand feet since the commencement of the Tertiary period. The Pyrenees, whose highest ridge consists of marine calcareous beds, of the age of our chalk and greensand series, while the Tertiary strata at their foot are horizontal, and reach only the height of a few hundred feet above the sea, seem to have been entirely upheaved in the comparatively brief interval between the deposition of the chalk and these Tertiary strata. The Jura, also, owe a great part of their present elevation to convulsions which happened after the deposition of the Tertiary groups. On the other hand, it is possible that some mountain-chains may have been lowered by subsidence, as well as by meteoric degradation, during the same series of ages in this quarter of the globe; and on some points shallows may have been depressed into deep abysses. But, on the whole, everything tends to show that the great predominance of land which now distinguishes the northern hemisphere has been brought about only at a recent period, and Sir Charles holds that the shifting of the continents is sufficient to account for the variations of climate. We have every reason to believe that before the Glacial epoch England and the Continent were united, and during the Glacial period England and North America were joined, viâ Greenland and Ireland. Mr. Dawkins says that England at that time was six hundred feet above its present level. If so—and we cannot question his conclusions—the Channel was then dry.

Fig. 684.—Cervus Megaceros (Megaceros Hibernicus): Irish Elk.—Post-Pliocene.

The “Great Ice Age” then came upon the world. For the information of readers who wish to peruse the whole history of this epoch and its causes, we may add that in Professor Geikie’s most interesting work, they will find full details. We can only refer to it.

The gradual decrease of temperature upon the earth, which was the cause of the Glacial period extending over the north of Europe, has been attributed to the eccentricity of the earth’s orbit; and here astronomy steps in to our assistance. We have read in the chapters on Astronomy, how the movement of the earth, like a top near the end of its “spin,” causes the “precession of the equinoxes,” and in connection with this phenomenon the earth’s orbit becomes more and more circular at certain periods of thousands of years, and goes away from the sun. We therefore receive the light and heat at a greater angle. Consequently, less heat is received, and ice is formed, as at the North and South Poles at present.

Fig. 685.—Drift Ice.

Doctor Croll has pointed out that the great eccentricity of the earth’s orbit existed about 210,000 years ago, when there was a difference between the nearest and farthest position of the earth and the sun of 12,000,000 of miles at least.[28] This is a very considerable distance even in the enormous spaces which intervene between us and the other planets of the solar system, and about that time the Glacial period arrived. Perhaps we may make this clearer by going back to the precession of the equinoxes.

The earth moves in an orbit called an ellipse, and the sun is not in the centre of this nearly circular path. We can now understand that the earth comes nearer to the sun sometimes and recedes at others. These points of nearest approach and greatest distance are termed perihelion and aphelion. In the latter case we are about 9,000,000 of miles farther from the sun than when in perihelion—that is, when the greatest “eccentricity” is reached. In addition to this the axis of the earth is continually changing in direction by reason of solar attraction at the equator. This shifting, as explained in the astronomical section, is very slight every year, and in the course of 24,000 years the conditions of the seasons will have completely changed round and back again,—for the northern and southern conditions will be reversed in our hemisphere. Day and night come twenty minutes earlier every year. We are now nearer the sun in winter as shown in diagram (page 497); when we change we shall be nearest the sun in summer and farthest in winter.

Fig. 686.—The Mer de Glace.

Doctor Croll, who has done much in his most interesting paper on changes of climate[29], tells us how this eccentricity of the earth’s orbit produced indirectly the Glacial epoch. He shows how, if in a period of the greatest “eccentricity” our winter came in aphelion, we should receive one-fifth less heat than now, but a correspondingly greater heat in summer. But if our winter under such circumstances fall (as now) in perihelion, the difference between winter and summer would be practically nil, because the sun during a period of the earth’s great eccentricity “could not warm the hemisphere whose summer happened to arrive in perihelion.” No doubt the sun’s rays would be very powerful, but the earth being covered with ice and snow could not be warmed; fogs would accrue and hide the sun, as at present in Antarctic summers, when the cold is very great. The warm ocean currents would be stopped, and the northern portion of our hemisphere would be, as it undoubtedly was, frozen over and covered with snow.

Fig. 687.—Mammoth and Irish Elk.

When we consider the millions of years since the earth is supposed to have been launched into space, we can imagine that the Glacial periods would occur frequently, and considering the very slow “precession” movement there, and the alternating tropical climate with graduations of temperature for thousands of years they would last long. The great Glacial period is computed to have begun 240,000 years ago and lasted 160,000 years with alternations of comparative summer; and so the years went on, season succeeding season, altering the appearance of the earth, and causing successive changes in the distribution of animal and vegetable life. Then the great mammalia, the mammoth and hippopotamus, with the hyæna, lion, and other felidæ came, and went when Arctic animals usurped their places. At the later Glacial epoch man must have arrived in Britain, and “this being so,” says Professor Geikie, “it is startling to recall in imagination those grand geological revolutions of which he must have been a witness.... He entered Britain at a time when our country was joined to Europe across the bed of the German Ocean; at a time when the winters were still severe enough to freeze over the rivers in the south of England; at a time when glaciers nestled in our upland and mountain valleys, and the Arctic mammalia occupied the land. He lived here long enough to witness a complete change of climate, to see the Arctic mammalia vanish from England, and the hippopotamus and its congeners take their places. At a later date, and while a mild and genial climate still continued, he beheld the sea slowly gain upon the land, until, little by little, step by step, a large portion of our country was submerged—a submergence which, as we know, reached in Wales to the extent of 1,300 feet or thereabouts.”

We find that the land underwent many subsequent changes; it rose from the sea, was again covered with ice, and many parts of Europe were devastated by immense glaciers—that of the Rhone extending for more than two hundred miles. Then came vegetation as the ice gave way, and luxuriance of the tropics reigned; more cold after that, then more heat, till the ice was finally driven to its mountain fastnesses, and “Britain for the last time became continental. Neolithic man came upon the scene; his palæolithic predecessor had, as far as Britain and northern Europe are concerned, vanished for ever.” The inquiry respecting the arrival and presence of man in Britain would lead us too far in pursuit. The fact has been established that man was living in the Thames valley while tropical animals were in the country, and he has been classed by Professor Boyd-Dawkins amongst the mid-pleistocene mammalia, and at that distant period, man as man, and not as an intermediate form connecting the human race with the lower animals, was present in Europe.

The stone implements which have been found in river beds and in caverns, associated with the bones of various animals, such as the elephant, rhinoceros, hyæna, bear, and others prove this. These very ancient and rudely-fashioned implements have been divided into two classes, the Palæolithic and the Neolithic, by Sir John Lubbock. First the stone implements were used, and stone was superseded by bronze and iron. Then we come to the historic period. In the neolithic period we find stone implements in the lake dwellings of Switzerland and Constance (as well as the Lake of Neuchatel), all of which have lately developed many treasures. Bronze tools have also been found, and so the gradual progress of man as a fashioner of weapons can be traced from age to age.

From the “river-drift” man we descend to the cave-man, who is supposed to have been identical with the Esquimaux. When Britain became an island the cave-man seems to have disappeared from our country, and in the prehistoric age the earliest of the present inhabitants came here, and brought with them domestic animals; then the Celts of the bronze age, and then the iron. The wild beasts gradually disappeared, and domestic ones occupied their places under civilized conditions.[30]

So we come from the “Glacial period” to the open door of history through the antechamber of the prehistoric time.

The prehistoric is the arbitrary division between the post-pliocene or pleistocene and the known “historic” periods of the world’s history, and we must dismiss it with a few general remarks, for the changes which we have attempted to follow are still taking place in the earth; volcanoes and earthquakes are unsettling the strata, and adding to the physical and geographical record which will some day have to be written by posterity and future geologists. We can see in those prehistoric times traces of men (hunters and fishers) existing with difficulty, mayhap, in the midst of enormous quadrupeds, and fighting for existence with the bears and many other formidable foes. We have noticed the stone ages, the rough and the smooth as they may be called, and we can picture the primitive agriculture and work of the neolithic man. But it is by no means to be believed that neolithic man in Britain was a race all over the world. We may assume that in eastern climes the human race were in a more civilized condition as improvements made their way slowly westward. Our island history commences in the time of Julius Cæsar. Eastern chronicles go back many thousands of years farther.

Fig. 688.—Carboniferous Flora.

It is so short a time, geologically speaking, since man appeared within the limits of history, that the earth’s changes, except from direct volcanic action or water erosion, are very trifling. The change is, as we said, continually proceeding; ceaselessly the earth is wearing away, and depositing her riches where she is undisturbed by civilization and man’s excavations and intrusions. The rock is worn by water; the grit is carried down and deposited to form sedimentary rocks as of old; the lime will continue to assist the coral to be built up; and the chalk cliffs will be born under the sea, and our organic remains shall be found to tell remote ages that we were an enlightened people. For all we can tell, and it is by no means unlikely another recurring cycle of Arctic and Tropical periods will in time pass over our earth; the bear and reindeer, the hippopotamus and the rhinoceros, may again inhabit our islands. If our generation be destroyed, the purely animal creation with the vegetable world will reign over the land, and new forests will deposit new coal measures for the support and comfort of a new generation of highly organized beings, when our remains shall have passed away to the borders of a “prehistoric” age.

We have seen in the foregoing brief sketch how the world has arrived at its present beautiful condition,—how it has been step by step prepared for us, how nature’s forces have been and are still working according to the immutable laws of the Universe. And, after all, how little we know! What scraps of intelligence only are we able to gather up from the boundless quantity of material which must have been laid down, yet what wondrous results scientists have been able to adduce from even these comparatively scanty specimens! The sea and land are ever telling us the same old story. Man’s research and Bible teaching are found hand in hand in cordial and reverent agreement. Nothing is altered since the day that the Divine command, “Let there be light,” went forth into space, and till the earth be destroyed the same forces will continue in operation, guided by the Hand that made it—“ever faithful, ever sure.”

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CHAPTER XLVI.
PHYSICAL GEOGRAPHY.

IGNEOUS ROCKS—LAND AND WATER—SPRINGS, WELLS, AND GEYSERS—SNOW AND ICE—THEIR EFFECTS.

In the foregoing pages we have chiefly considered the stratified rocks, but we are now approaching another branch of our subject—viz., “Physiography,” which, as distinguished from the usual so-called Physical Geography, will deal with the phenomena of the earth, air, and water, thus leading us to Meteorology as a conclusion.

We have arrived at a certain knowledge concerning the Earth as a planet, her place in the universe, and the composition of the “Crust,” as it is termed. We have examined the stratified rocks, which include sand and gravel, stones, and boulders equally. To a geologist they are all “rocks.” We must now examine the igneous rocks, which bear an important part in the structure of the Earth, whose surface we have now more minutely to examine. It has already been stated (p. 571) that igneous rocks have been upheaved while in a state of fusion—that is, while in a melted condition. These igneous, or fire-produced rocks, are divided into classes, just as the unstratified rocks are, and the divisions are called the Volcanic and Plutonic, including “Basic” and “Acidic,” according as they are possessed of less silica or more.

Sometimes the igneous rocks are classed as volcanic, trappean (from trappa, a stair, such as in the Giant’s Causeway), and granitic. The volcanic in such case being the modern or upper rocks, such as lava, scoria, etc., which, having been cast up by volcanoes, are of comparatively recent formation.

The Volcanic rocks, then, are of recent date, comparatively speaking; they form the constituent portions of the volcanoes of the present day, and are found as basaltic formations. They are traced as far back as the Tertiary period of the globe. Amongst the volcanic rocks we find basalt, augite, porphyry, serpentine, pumice, pitchstone, felspar, etc. But no doubt volcanic action has been going on ever since the beginning of the world as it is now, and will continue to do. It is somewhat curious that the very old igneous rocks should not be more evident.

The Plutonic rocks do not differ essentially from the foregoing. There is less quartz and more hornblende; and if the ages during which these formations have been existent in the earth-depths after they became solidified be considered, the differences will be fully accounted for. The greenstones and syenites are prominent amongst the plutonic series.

These plutonic and volcanic rocks are separated into basic and acidic, as already remarked, but the line cannot be drawn very distinctly. Granite is the chief plutonic (acidic) rock, and we frequently find it forced upwards into other strata, its essentially eruptive character being thus decided. That granite must have taken an immense time to solidify and crystallize is evident, for no new granites are ever found. We find granite in all the old mountain chains—such as the Grampians in Scotland, and the Wicklow mountains. Our chief European (active) volcanoes are, so to speak, modern, as may be supposed when their constituents are known. It may be said that granite was first deposited as sediment heated by subterranean fire, and forced up by thermal action of water to the mountains, where it is uncovered by a slow process of denudation and surface washings of the earth.

Now without at present going any farther into the causes of volcanoes we can see at a glance that the eruption of the igneous rocks must have created a marked and essential difference in the physical geography of the globe. It is to these eruptions that the dislocation and disturbance of the stratified formations are due. The igneous rocks present ridges in the mountains; sometimes they are rounded at the summits, while the aqueous and metamorphic rocks are disposed in layers.

Fig. 689.—Crater of Popocatapetl.

These two classes in their varieties form the land and the crust of the earth, which is ever being acted upon by air and water. The ice, again, polishes and scratches the valleys in which it moves. The loosened boulders that tumble from the mountains are carried down by the ice, and deposited in the glacier moraine, whence flows a stream. By degrees the stone is ground up, and carried away in the water to form sediment in a “delta” at the embouchure, or to lie beneath the surface and form rock once more. The igneous rocks, composed of lavas and ashes, are volcanic rocks, deposited deep down, and then after the lapse of ages disclosed by the action of air and water.

The consideration of the land and water upon the globe shows us that they are distributed over the earth very unequally. There is nearly three times as much water in our planet as there is land, and these proportions could not be altered without giving rise to phenomena, the results of which cannot be properly estimated. Our earth has an area of 197,000,000 of square miles; about 52,000,000 of this is land, and about 145,000,000 of it water; so about three-quarters of the globe is made up of water. The first portion of our subject therefore should be directed to the examination and consideration of water, and the phenomena which arise from its presence upon the earth.

Fig. 690.—Distribution of land and water.

We need not go into details which every geography indicates. We will try to trace the sources, not the plain effects, which all can afterwards study from special books. In a preceding portion of this volume we have explained the chemical composition of water, and we showed by experiment that it is a fluid composed of oxygen and hydrogen gases, in the proportions of one to two volumes respectively. No matter in what form water may appear,—as water, as ice, or as steam,—these proportions never vary in pure water (see[ p. 352]). But water on the earth is seldom, or never, pure. We know the difficulty we have to procure good drinking water, and though it may be filtered, there will remain natural salts, which are found in different degrees in all water upon the globe. We know the rain, which is perfectly pure when condensed from the clouds, absorbs carbonic acid, etc., from the atmosphere. We have shown how this water as soon as it comes upon the earth attacks the rocks, and as it progresses carries away lime. After descending deep down, it rises again in the form of Springs.

Now what are these springs? They are the result of percolation of rain-water through certain strata. When water falls it is absorbed into the ground, unless it happens to rest upon an impermeable rock, in which case it becomes a rivulet. But it can penetrate between the atoms of many rocks, and thus falls through sand and harder rocks, till it reaches a stratum which will not receive it—like clay. We then find that it will flow away in a spring, or if tapped will be an Artesian well. These water-wells are of very ancient date, but the name is more modern.[31] The springs flow out, and develop, with the assistance of tributaries, into rivers. These again receive more tributaries, which swell the volume of their waters, and widen out, carrying millions of gallons hourly to the sea with sediment and gravel and stone.

Fig. 691.—Distribution of land and water.

Water has enormous power of disintegration. We have only to cast our eyes upon the illustrations in any volume of continental travel in Europe or America to perceive the gorges and cañons worn out by the resistless and frequently gently-flowing river to estimate the part which water plays in Physical Geography and Meteorology.

But springs occur not only in the case mentioned; there are mineral springs, hot springs, and oil springs, all following the same rules of nature. The Artesian well has been mentioned. The Geysers of Iceland have often been portrayed, and are amongst the most wonderful phenomena of nature. These will serve as a type of the other thermal springs, of which the districts of the Yellowstone in North America afford perhaps the most extraordinary instances. These are intermittent springs, and the water rises to a great height, at intervals of about an hour and a half; and after many successive attempts, or trials, as it were, the geyser shoots up to a great height enveloped in steam.

The cause of these well-known phenomena have been explained by Bunsen, and it has already been referred to. We know that at a certain air-pressure water boils at 212° (Fahr.), but on mountains at less pressure it will boil before that degree, because the air is rarefied. So conversely, under the ground, it may reach 212° without boiling. So the surface (warm) water falls, and reaches a high temperature before it is converted into steam. When it is so converted, the vapour is formed very rapidly, and the expansive force is tremendous, shooting up the water and all the contents of the tube with terrific violence, and with a beautiful effect. Pressure therefore alters the boiling point of water.

Fig. 692.—Geyser of the Yellowstone.

The mineral springs of Bath and many continental towns owe their properties to the solvent power of water, which assimilates the mineral atoms and gases. They arise just in the same way as the ordinary spring, the taste and smell depending upon the soil and strata. Perhaps the oil wells are the most curious phenomena of this kind. They are excavated upon the Artesian principle. The petroleum is bored for, as we bore for water, and the oil rushes up with great force, and in enormous quantities. Gas wells are also to be found in Pennsylvania, and have supplied towns with gas for years. Both these Artesian wells are caused by the decay of vegetation. The gas is in the coal formation, and the oil has been pressed out from vegetable deposit, and as anthracite is a stony coal, petroleum is a kind of coal-tar, of natural formation.

Fig. 693.—Colorado Cañon (effects of water erosion).

We have alluded to the river, which emerges from the spring, which has fallen as rain. But there is another, and, to many minds, a much more interesting form of the universal fluid we call water. This is ice. Familiar as ice is, either to the stay-at-home invalid, the skater, and the traveller, there is a great deal to be said about it. It is a subject we would dwell upon had we space, for the remembrance of many a pleasant hour passed upon snow and glacier call upon us to go back again, even though only in imagination. No one who has not climbed the glacier—even the Mer de Glace to the Jardin, now such a common excursion—can fail to be struck with the beauty and grandeur of the scene presented to him, and to carry away a fond recollection of the icy regions he penetrated.

For the ordinary hard-working man there is no change, no rest so truly beneficial as a trip amongst the mountains and snowfields of Europe. He need not be a climber; that is, a climber like Tyndall or Whymper, those giants of the Alpine Club. But a stroll up to the Bel Alp, the Æggishhorn, the Riffel, the Montanvert, or the Grimsel, will give the average pedestrian some of the finest glacier scenery in Europe, and which may, we believe, compare with any in the world for beauty. These glaciers—ice-rivers—we will now consider briefly. We may take the Mer de Glace as an example (see the illustration, [p. 596]). That gives us a very fair idea of the ice-river, but the cut below is a good specimen of a glacier.

Suppose we start up from Chamouni, or come across from Argentières, we shall reach the Montanvert by ascending through the wood, or by the “Chapeau,” across the ice-sea. As we take the former course, we walk alongside a white-flowing and rapid river, the Arve, which unites with the Rhone below Geneva. This river divides, and if we keep alongside one (the right or south branch), we shall reach the moraine and the icy grotto, from which the water issues. It is in this way many large rivers are born. The Rhine, the Rhone, the Aar, the Ticino, have all of them their sources in the ice. The Visp and the Sass waters are other almost equally well-known examples.

Fig. 694.—Source of the Rhine.

There used to be a grotto or cavern, into which the tourist could enter at the source of the Arveiron, and here the beautiful blue of the ice could be studied. From this place the Chapeau is reached, up a stony path amid the trees, and from the top outside the hut we can see the Mer de Glace all broken and contorted. The frequently occurring roar of a falling rock which heat has deprived of its icy support, or the cracking and tumbling of ice-blocks, may be seen and heard in the forenoon. But the grandeur and majesty of the ice and snow-clad mountains is best enjoyed by moonlight.

Fig. 695.—Glacier table.

On the ice we shall see huge stones and gravel and grit, which have been carried down by the ever-moving glacier, which is denuded in its course, and worn down upon the surface as it slides, scraping and grinding the valley through which it flows. By passing along a path now made easy by irons, but formerly without supports or guards, the surface of the glacier will be reached, and a man with a hatchet will cut steps for the timid traveller. We are now upon the deep ice-river, which has its springs in the snowy regions of the Col de Géant, in the snow which is continually falling upon the heights, and draining away to water again to form a river.

Thus the circle of events is completed,—snow, névé, ice (glacier), water, which last is again absorbed into the atmosphere, and again descends as rain or snow. And this is always going on by the action of the sun. It may here fairly be asked how snow becomes ice. Why does not the snow turn into ice at once, and form a glacier at the top of the mountain as well as at the bottom? We will endeavour to make this clear. Snow is composed of crystals, which assume certain definite forms, and when first the flakes fall they are soft and powdery. By degrees they melt a little, and when unconsolidated form what is termed névé, the border line between ice and snow. This semi-icy snow descends under pressure, and, as it increases, the glacier is formed by huge blocks and masses being pressed together on the steep slopes of the mountains. Thus the glacier descends, rounding off rocks, and scouring as it goes, moving at a certain estimated rate daily,—about twenty inches on the average,—carrying stones and débris which form the moraine, and finally when the high temperature in the valley melts the ice, it issues forth as a river into the plain, or bounds down the mountain side in a cascade. An excursion—and one by no means dangerous if a guide be taken—to the Jardin, near Chamouni, will reveal many interesting features of glacier formation, and of the glaciers themselves.

Physical Geography is therefore very much indebted to the action of water as a fluid or as a solid. In the former condition it erodes the rocks, carries down the stones and gravel and sand, forms deltas at the mouths of rivers, and elevates plains by overflowing its banks and depositing sediment. Water gives beautiful scenery, and the ever-changing features of the landscape are due to it. From the time the spring emerges to the time when it has developed into a river, bearing fine ships upon its restless waters, the universal fluid is always at its work of destruction and benefit combined. From the limpid stream we pass to the salt ocean, the reservoir of all the waters of the globe.

Fig. 696.—Life under water.

We have in this chapter briefly considered two very important forces which have much to do with the varying conformation of the earth—viz., fire and water in their results of volcanic action and erosion. The sea will tell us something more.

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CHAPTER XLVII.
THE SEA AND THE SKY.

THE SEA—SALT WATER—WAVES AND THEIR EFFECTS—UNDER WATER—THE FLOOR OF THE OCEAN.

From our childhood the sea has been the companion and playmate of thousands, the seashore their playground. Men have selected it for their professional training and livelihood. Authors write of it, poets apostrophize, scientists lecture upon it, and fathom it, bringing up from its depths many a new fact and illustration for those who cannot study it for themselves. There is nothing like it, nothing more majestic, more beautiful, more life-giving than the ocean—nothing so changeable nor so true.

From the days when we could toddle along the beach, picking up the shells, we have wondered at the ocean—What was beyond it? What did it conceal?

“What hidest thou in thy treasure-caves and cells,

Thou hollow-sounding and mysterious main?”

Let us endeavour to find out.

The first thing that strikes us is the saltness of the sea. Sea water is salt. Why? One reason is because salts are carried into it by rivers, and besides, it is more beneficial as salt water. But let us look at the facts. We know that the earth contains many “salts,” as we can see by the saline springs. We have already given the chemical constitution of sea water, but it will be useful to repeat the proportions.

Water	964·74372	grains.
Salt (Chloride of Sodium)	28·05948	”
Chloride of Potassium	0·76552	”
Chloride of Magnesium	3·66658	”
Bromide of Magnesium	0·02929	”
Sulphate of Magnesia	2·29578	”
Sulphate of Lime	0·40662	”
Carbonate of Lime (with traces of Iodine and Ammonia)	0·03301	”
	1000·00000	”

Some portions of the sea are not so salt as others, or, in other words, not so dense, and the saltness of the water prevents it being frozen so quickly as fresh water, which freezes at 32°. Salt water requires to be reduced to 28° before it freezes. Besides the various constituents mentioned above, sea water has been found to contain boron, bromine, strontia, etc., and even silver, for the copper of ships has been found to be impregnated with that metal.

Fig. 697.—Going out.

If there is so much salt in the sea, it may be asked, why does it not continually become greatly saltier by additions. The reason is because tons of fresh water are continually pouring in, and though we can scarcely doubt that the sea is becoming gradually more salt as years pass away, the increase is very slight. On the other hand, evaporation is carrying water into the air and leaving the salt behind it. In seas like the Red Sea, where there is a great deal of evaporation and very little addition of fresh water in comparison, the water is extremely salt and bitter. The Baltic has little salt relatively to some parts of the Mediterranean.

Supposing that, as some allege, there are rocks of salt at the bottom of the sea, we must remember that springs of fresh water frequently bubble up to the surface of the ocean. This is a very curious phenomenon, and has been attested by Humboldt. He states that near Cuba these springs arise with considerable force, and the vessels trading on that coast get supplies of fresh water from these ocean springs. There is, or was, a similar uprising in the Gulf of Spezzia, and fresh water crustacea inhabit these localities. These occurrences prevent the sea from becoming too salt by evaporation. When salt water becomes tainted it is very offensive—much more so than fresh water. If, therefore, the ocean were not continually in movement, it would be very injurious.

So much for the water of the sea; let us now see what it does. We will glance at the surface ere we plunge into the depths.

In childhood, and even in after years, we most of us delight in watching the waves of the sea. What finer sight than that we can obtain on the bold Cornish coast with a westerly wind, when the great Atlantic waves come rolling in and dashing up to the tops of the Tintagel cliffs, wearing and grinding them away; hissing up the sands at New Quay, or thundering on the shores of “Bude and Boss”! Then the wind abates, the sea goes down, the billows become waves, the waves to wavelets grow, less and less, until there is a mere ripple on the surface which is never still. The mighty heaving of the ocean breast is the peculiarity of the sea.

Fig. 698.—Sea waves.

Yet, again, as we stand to watch the waves, or run from them as they sweep in foam upon the sloping sand, we shall find that they increase or decrease in force, and the level of the water rises or sinks by degrees. The tide is flowing or ebbing as the case may be. So we know the surface has another—a current motion—besides the undulation of the water. The currents of the ocean are very valuable attributes, the Gulf Stream in particular bringing us warmth and, indeed, rain. There are three movements of the ocean—waves, currents, and tides.

The waves, perhaps, interest us most, as they come rolling in with irregular force, but all mightily impelled by the wind. We have all noticed the ripples on a puddle; the same action of the wind produces the grandeur of the waves of the ocean. The wave comes rolling in before the wind to break against the rocks or beach, and another forms to break in its place; the higher the waves the more quickly they appear to move. But when the wind has subsided the rolling, or “swell,” remains,—a long, lazy, undulating motion—a rocking to sleep of the billows of the sea. Without a ripple on the surface these huge rollers will glide towards the shore and break upon the shingle with a roaring sound which can be heard for miles, dragging the pebbles after them as they recede with a rattling like bones and marbles. The pebble ridge at Westward Ho! will illustrate this vividly at times, the sound being heard far inland like continuous thunder, and on a calm night, when there is no wind stirring, the roar of the ground swell is weird and mysterious in the gloom.

Fig. 699.—The Piroroco on the Amazon.

The height of waves is very varied. Observers say that forty-four feet is about the highest-known wave from hollow to crest. Waves of thirty-five feet have been often met with, and off the Irish coast and in the Atlantic sailors tell of waves “as big as houses.” But houses differ in size as do waves.

The rate which waves are estimated to travel varies with the wind-propelling force. The average hurricane wave travels at about forty-five miles an hour. But earthquake waves—those set in motion by subaqueous disturbance—have been known to travel at the rate of six hundred feet in a second for thousands of miles across the ocean. Such a one occurred after the earthquake which destroyed the town of Arica in August 1868, and the wave crossed the Pacific to Chetham Islands, 5,520 miles, in fifteen hours and twenty minutes. We have many of us seen the great tidal waves, or “bores,” which at certain seasons rush up our rivers—the Severn, for instance—with great violence, and at times forty feet high.

These tidal waves are also experienced in the Ganges, the Amazon, and at Bordeaux, as well as in China and elsewhere.

Fig. 700.—Tidal Attraction.

It may well be imagined that the tides also affect the land, and the theory of these ocean movements is a very interesting study. We have already referred to it under Astronomy, for the Sun’s and Moon’s attraction is the main cause of the phenomenon, which is so familiar and yet so strange. But the consideration of the tides must be again entered upon here ere we proceed to view the effects of the sea upon the land, and how the physical geographical features alter.

Isaac Newton rightly attributed the cause of the tides to the attraction of the moon and sun. Spring tides occur when both luminaries are above the meridian, and the neap, or low tides, happen when the sun and moon are farthest apart. The highest tides are perceived after a new or full moon; the lowest, after she has passed the first or third quarter. In January the spring tide is highest of all, because the earth is nearest to the sun then, and his force of attraction, added to that of the moon, causes a very high tide. With the assistance of the accompanying diagrams we shall be able to make the tidal phenomena clear.

Fig. 701.—Tidal Attraction.

Suppose the moon to be at M, the point J (the sea) will be nearest to the moon and will be attracted, while the earth will exercise a retarding power to a certain extent. This attraction of the water from its usual level causes a kind of vacuum, into which the surrounding water flows and causes a high tide at H. At the opposite side the earth, not the water, is most attracted, and then the water rushes in to a certain extent to fill the vacancy left by the earth’s movement towards the moon. Another high tide is therefore caused at L, but not so high as the tide upon the opposite side, as the Moon is so much nearer the latter. The tide, then, is only the natural movement of the sea water to fill up the space the earth and other portions of the watery mass have vacated in obedience to lunar and solar attraction, which is, to a certain extent, counterbalanced by the attraction and resistance of the earth.

The neap tides are caused by the opposing forces of attraction of the sun and moon. The sun, as it were, pulls one way, the moon the other. The latter (being nearer) having twice the power of the former, causes a tide indeed, but it is a low one. The spring tide occurs when sun and moon together attract the water.

The effects of the rise of the tide are sometimes very disastrous, and when the wind assists the sea, and heaps up the water, the sight is grand in the extreme. On the coast of Schleswig, at Hallingen, the sea has washed away a whole cluster of islands, and now the waves cause tremendous inundations. About every six years, on the average, a great flood happens for such trifles as a high tide are of no account. In 1362 and in 1834 terrible destruction was wrought; the coffins and bodies were washed out of the graves. Piles of débris are then washed up, and sand and gravel accumulates for a time till again carried away.

Travellers to France will notice the “dunes,” or sandhills of Calais, as the train winds its way to Boulogne. We find that whenever the shore is flat the shingle and sand are blown inwards and form “dunes,” and the sand is distributed far inland, checking all vegetation, and altering the features of the country. The wearing away of rocks by the water, the continual undermining of them by the waves, and sometimes the disengagement of great blocks weighing many tons—all these effects of the sea tend to alter the appearance of the land. We may observe the denudation in many places along the coast—the caves, holes, and tunnels eaten out by the water. In Norway the “Fiords” are very remarkable. They were formed by the upheaval of the land, and tell us of the glaciers which once filled them up. Thus by ice and water the solid land is ground down and eaten away hourly, daily, and for countless centuries, changing the place of the hard rock into a standing water, and the flintstone into a springing well.

Fig. 702.—The Dunes.

We must now plunge beneath the waves, never fearing the rough surface; we shall find all smooth and quiet at the bottom of the sea.

The Bottom of the Sea.

What can we tell about the bottom of the sea to which no man has ever reached living, and from which we have no information? We can lay our telegraph or telephone lines beneath the waves, and far from the restless waves in those quiet depths where no billows can reach. What treasures must lie hidden at the bottom of the sea! The treasures, the gold and silver, the merchandize, the wealth of centuries. The sailor lies sleeping there

... “Serene and safe

From tempest and from billow;

The storms that high above him chafe

Ne’er rock his peaceful pillow”!

What can we hope to find at the bottom of the sea we cannot reach? Yes, but we can reach it. By sounding with Brooke’s lead (a cannon ball, as shown in the illustration), we can arrive at a certain knowledge of the composition of the ocean bed. The right-hand figure of the two is the lead when being lowered, and while it is sinking the cord remains tight. So soon as it touches the bottom the weight of the cannon ball divides the line, and the tube is easily drawn up again. It has been well greased, and so in the cavity of the rod some shells and sand are found adhering. These fragments tell us the composition of the bottom of the sea.

Fig. 703.—Brooke’s Lead.

Here we find tiny shells, just as we find them in chalk, the same formation as that which piled up the cliffs which have risen from, or been discovered, by the sea. By other ingenious contrivances water can be fetched up from the bottom of the ocean, and the temperature can be gauged all along the sounding line. The expedition of the Challenger brought many interesting facts to light. Far down in these solitudes are marine animals,—crustacea, star-fish, seaweeds, and shells,—all of which are carried up by the dredge worked by a steam engine; for the resistance is very great, and the weight supported at the depth of two miles must be considerable, and is equal to four atmospheres. A thermometer has come up crushed even in its iron case, and so the creatures which inhabit and find means to live at the bottom of the sea must be specially fitted by Nature for the locality.

The configuration of the ocean bed has given rise to many different opinions. It has been maintained that there are mountains and valleys, hills and dales underneath the water, all clothed with marine vegetation, equal in height and depth to the terrestrial hills and vales. Again it has been declared that the ocean bed is level; but we find raised portions, which we call islands, which may be the tops of mountains, or portions of the mainland separated from their parent continent by an inroad of the sea, as are our islands of Great Britain.

The sea-bed, however, is very irregular. We find deep and steep valleys, and high hills, but the picturesque peaks caused by the action of air, frost, and water on earth are not, of course, represented under water. Between the Irish coast and Newfoundland we are told the bed is level for nearly four hundred miles. There is a deep declivity before we reach this plain. The centre of the Atlantic is a plain, and on it the most volcanic islands rise, such as Ascension and the Azores. Between England and Greenland there was at one time a land communication, as we have remarked under Geology, and there are submarine terraces now. [An immense river once ran through Western Europe somewhere about where our islands are.]

Fig. 704—The Drag Net.

Under the Atlantic we have remains of foraminifera and other tiny animals, with red clay and volcanic remains which must have been of submarine origin. The Pacific shows us tops of mountains as islands (Hawaii Isles), and an enormous range must be hidden beneath the waters. What a change in the physical geography of the earth a slight sinking of the water of the ocean would make; England and the Continent would be united, and many sea-mountains (islands) discovered. The greatest ocean depth is four miles and a half, but in many places a few hundred feet less depth than at present would reveal many changes in the land.

Every year since the world has gained its present form the streams and rivers have been pouring water, and carrying mud, stones, and gravel ceaselessly into the ocean. In addition to this, the surface water washes the stones away, animals (corals) build up islands from the depths, and take up space in the ocean. We know that if we put our hand in a basin full of water we displace a quantity of the fluid; so we might imagine that, the sea being already full, every island formed would tend to an overflow of the sea, and the land would be thereby buried. That the sea does encroach upon the earth we know, but it also recedes. Here is the balance of Nature.

Rivers pour in water and material. The sun absorbs the water and prevents overflow; tiny animals make shells from the material. All the causes we have mentioned tend to permit the encroachment of the waters, but volcanic action and even earthquakes act also to neutralize this tendency by upheaving hills and mountains, which prevent the invasion of the sea by its elevation or by land depression. We have seen in our chapters upon Geology how the ocean beds have been upheaved, and remains of marine animals are daily found upon our highest hills. Thus the forces which sometimes cause such destruction in the earth are the means whereby the waters are kept in their places. But for volcanic action the land might all disappear by denudation and continual wear and tear, and be deposited at the bottom of the sea!

If it were not for currents, of which many defined ones exist in the ocean, and the never-ceasing flow and ebb of the tides, the sea would soon lose its purity and clearness. Though the water is salt and becoming salter, animalculæ and all kinds of plant-animals would still increase and multiply; so the decay of animal and vegetable matter would quickly render the ocean a source of pestilence and death to mankind, and be most injurious to animal life generally. But the movement is so ceaseless, and the various fish and mammalia (whales, for instance), by preying upon each other, as other animals on earth do, keep up the balance of production, and the organic matter deposited in the sea is also cleared away.

That the constant currents of the sea prevent the formation and growth of seaweed is clearly shown by the great “Sargasso Sea,” or tract of weed (Fucus natans), called the Gulf-weed. This great tract embraces thousands of square miles, and is situated in the very middle of the Atlantic Ocean, where there are but few currents; but surrounding it is the Gulf-Stream, an enormous current of water running at a regular rate of four or five miles an hour. This Gulf-Stream is supposed to be caused by the same laws and influences which determine the trade-winds—namely, a constant rarefaction of the water at the tropical parts of the earth, and a corresponding condensation at the Arctic portions, for warm water is much lighter than cold, and when the waters of the tropical regions become lighter, the heavier waters of the cold regions pressing down more forcibly tend to raise them above their proper level; they therefore flow towards those very parts which have sunk down by their contraction, and a constant current takes place; this current is the Gulf-Stream. It runs from the Gulf of Mexico northwards towards Newfoundland, turning by Iceland towards the British Isles, by France and Spain, onwards to the coasts of Africa and South America, the West Indies, and again to the Gulf of Mexico, although the return current does not go by the name of Gulf-Stream. This great stream of water, warmed by the tropical sun, serves the same two purposes fulfilled by the trade-winds—namely, a circulation and distribution of the superfluous heat of the equatorial regions, warming the northern countries; and cooling, by the return of under-currents, those in the tropics. The fogs of Newfoundland are caused by the great current of warm water entering the cold region and carrying with them surface-currents of moist air, which the cold condenses into fog, just as the breath is visible in a cold atmosphere. England owes its moist and mild climate to the same cause. The depth of the Gulf-Stream itself is very little. It is a mere layer of warm water. (See Sir George Nares’ reports of the Challenger expedition.)

Fig. 705.—Atoll, or Coral Island.

In the foregoing pages you have now seen, and, we hope, gained, some information concerning the sea sufficient, at any rate, to induce you to enter more deeply into the subject than we can at present do. We have learnt how the sea water is composed, and what goes on on the surface. We have discussed waves, and referred to tides and currents, the wearing away and the renewal of land by the sea; we have dived beneath the surface, and found something to interest us at the bottom of the ocean. As we come up again we are surprised to find islands or reefs where none existed when we went down. What has caused this sudden appearance? They may have been slowly raised to the surface by coral insects, or suddenly by volcanic action. Let us consider the coral, which plays a very important part in our Physical Geography, before we proceed to the volcanic island.[32]

The low-lying islands are those formed by the skeletons of the coral insects, and the Coralline Islands are some of the most wonderful productions of nature. They are only found in warm climates, between the twenty-eighth degrees of north and south latitude, and limestone pure and simple is the chief component of the coral reef, as it is of the mountains erupted from the depths of the sea. “The detritus of corals, echinodermata shells, reticularia, and other living creatures,” says a writer on this subject, “deposit not only the salts of lime extracted from the ocean, but their own dead bodies to form the hard substance of the rock.”

Fig. 706.—Gorgonia guttata (natural size).

Fig. 707.—Coral (Madrepora brachiata).

The coral insect is a zoophyte (Anthozoa), which, as may be seen from the illustrations, assumes curious and elegant forms, and the coral it produces is a limy or calcareous deposit, which is fixed upon a rocky base. As years go on these accretions become greater and greater, and at length rise above the water. When a little distance below it, the reefs form dangerous and frequently unsuspected barriers, upon which ships are wrecked. The red coral is dredged up from the Mediterranean, where there are extensive coral fisheries. This coral is found deep in the water, and never rises to the surface. Formerly there were coral reefs in the European seas, but the changes of temperature stopped their production. The “atolls,” or circular coral reefs with an opening at one side, have been described by Professor Darwin. “Who,” says the great naturalist, “would not be struck with wonder and admiration on catching sight for the first time of this vast ring of coral rock, often many miles in diameter? Sometimes a low green island is seen beyond it, with a shore of dazzling whiteness; outside is the foaming surf of the ocean, and within it a broad expanse of tranquil water, of pale green colour and exquisite purity.” These “atolls” mark the situation of sunken islands, and the extension of them and the barrier reefs would seem to indicate a slow but decided sinking of the bottom of the Indian and other oceans; but the “reefs” tell us that the land to which they are attached has not become depressed, and may have become elevated. We may then conclude that a continual rising and depression of the land is taking place in various oceans, indicating a sinking of the ocean bed in one locality and the result of volcanic activity in another, for no active volcanoes are found in the regions of depression.

Fig. 708.—Spicules of Gorgonia (magnified).

We must now leave the sea and come to land again, to consider volcanoes and volcanic action there.

Volcanoes and Earthquakes.

The various phenomena of volcanoes form a subject very difficult to be explained, as it is impossible to ascertain positively the cause of volcanic action. Whether the earth is interiorly a mass of molten rock and fire, or whether the heat is created by the intense contractile force and movement of rocks, and their motion thus developed into heat aided by chemical combination, we cannot absolutely determine. The theory restricting volcanic phenomena to the upper crust of the earth, by supposing the local accumulations of hot liquid masses of rock, which are forcibly emptied by the expansion of vapours, may perhaps be found the true one.

The majority of the volcanoes are found near, or at no very great distance from, the sea. We may therefore expect to find that water has something to do with the eruptions as it has in the case of the Geysers. But this hypothesis will scarcely hold good in every case, though volcanoes of later ages are limited to regions very different from those in which volcanic action used to be. For instance, in America we have only volcanoes on the Pacific side, and the Andes furnish several. Mexico, Central America, and California possess many volcanoes, and as far north as Alaska we find Mount Elias. There are plenty of extinct volcanoes in Europe, but the Mediterranean produces the active vents; and about the Red Sea and the Caspian, and even in the central chain of Asia, there are volcanoes far from water. The Hawaii isles, on the other hand, are all volcanic, and Australasia furnishes us with remarkable specimens; so altogether the testimony tends to prove that where volcanic remains are apparent the sea had at one time been, or now is, near at hand.

Burning mountains have been familiar to us from our childhood in pictures, and by stirring narrative of destruction wrought by them. The volcano is generally a mountain rising to a cone, but Vesuvius presented quite the appearance of a hollow basin at the top, before it suddenly broke forth and buried Herculaneum in ashes. Von Buck visited it in 1799, and declares it had at one time risen, like an island, from the sea. There are about two hundred and seventy volcanoes at present in activity; four in Europe; eleven in Iceland and Jan Meyen’s land; in Asia, ninety-three; in Africa, twenty-six; forty-six in North America and the Aleutian Isles; twenty-seven in Central America and the Antilles; in South America, thirty-one; and twenty-four islands with volcanic tendencies largely developed. There may be many more “resting.”

Volcanoes, then, are openings or vents which communicate with the melted rock within the earth, and the conical form of volcanoes is owing to the deposits of volcanic matter as it falls from the opening called the crater. If we let a small spade full of mould run through our hands, or from the spade, it will form a small cone, the heavier particles sliding to the base at a certain slope. Thus the volcano builds its own hill, and inside the crater we find cones from which smoke and steam issue. These cones within the cone are the points of issue of vapour and smoke, miniature volcanoes making up a whole.

Fig. 709.—Eruption of Vesuvius, August 26th, 1872.

The signs of eruptions are much the same, and usually occur a couple of days before the actual outbreak takes place. First smoke is perceived, perhaps, and the escape of various noxious gases accompanied by earthquakes occur. Now the eruption may commence and blow away the summit of the mountain, as in the case of the commencement of the catastrophe of A.D. 79, when the whole side of Vesuvius was torn away, and continuous showers of ashes fell for days and nights, burying everything, while the hot lava poured down the sides. Stones and ashes with vapours are hurled into the air. Clouds of steam are formed, and vivid electrical discharges take place in these clouds, while water dashes down, carrying stones (“volcanic bombs”), and reflected lurid flames from within are cast on the steaming clouds, which look like fiery columns. Then the lava issues in a white, hot, steady, irresistible stream, covering everything, and burning up all vegetation.

Fig. 710.—Birth of a volcano.

New volcanoes are continually in process of formation, and at Santorin for hundreds of years volcanic action has been busy in forming islands. These violent efforts of Nature frequently give rise to earthquakes, which are the most destructive of natural convulsions. The records of late occurrences are fresh in the minds of all readers, and need not be specified. The slow subsidence and gradual upheaval of the land is still going on, but we are frequently startled by the account of a rupture of the ground or the destruction of a portion of a city.

The motion of the earthquake is generally in a direct line, and undulating. Sometimes what are termed vertical shocks arise and destroy solidly-built edifices. Mountains have been overturned by earthquake shocks, and trees have been twisted round. Sometimes the ground yawns into enormous fissures. The sea is tossed into great waves and encroaches upon the land, and when the sea recedes the recession of the water is followed by a more terrible invading wave sweeping all before it. Earth tremblings often occur far away from volcanoes, and without any visible connection with volcanic action. There are many aspects of land and water which the student of geography will remember, but which need not be separately treated of. We must, however, refer to plains, plateaus, and lakes. The mountains also play a most important part in Physical Geography and in “Climatology,” as they collect the vapours for rain, and make the valleys fertile, and thick with vegetation. We have spoken of the mountains under Geology, and the various formations and strata will be found enumerated there, but now we have to do with the mountain chains in their physical aspect as regards their shape and appearance on the globe.

Fig. 711.—Earthquake fissures.

Any elevation rising from a base more than 1,000 feet may fairly be termed a mountain, and solitary mountains are usually volcanic, because eruptive rock does not produce chains of mountains. The origin of mountains is probably due to the contraction and compression of the crust of the earth—not merely the surface, but the whole thickness between us and the supposed molten interior. Mountains did not exist from everlasting, for the very good reason that they are (in most cases) composed of stratified rocks. Stratified rocks are sedimentary rocks, and must have been deposited below water, and hardened long before they were thrust up by pressure. Moreover, we find (as has already been explained) shells and remains of marine animals on the higher summits, which prove to demonstration that these mountains are composed of rocks which were laid down under the sea.

Professor Dana was one of the first geologists to advance the theory that contraction and lateral displacement are the causes of the elevation of mountains. A very good illustration of this theory was made by Chamontier, who covered an india-rubber balloon with a thick layer of wax, and when it had hardened sufficiently he pricked a hole in the bladder, which immediately contracted, and the wax at once rose up into tiny similitudes of mountains, showing in a sufficiently clear manner that such protuberances may be produced by the pressure of the earth’s contraction, and in such a mass as our earth the elevations would naturally be very great.

Professor Geikie has shown how, by a very simple experiment, the contortion of mountain strata is effected by pressure. A number of cloths or towels placed flat on a table represent the sedimentary rocks. Place a board with a weight on the top, and the towels will remain flattened. But by holding two boards at the sides and pressing them together (the weighted board still remaining), we shall find the towels crumpled and upheaved like the Jurassic strata shown in the illustration (fig. 712). Professor Heim calls the central masses wrinkles of the earth’s crust. So the Alps were pressed up or heaved into the air, the weather—rain, frost, snow, and sunshine—imparting the infinite variety of “Horn,” “Needle,” and “Peak,” so expressively applied in Alpine nomenclature;—the Matterhorn, Wetterhorn, Weisshorn; the Pic du Midi, Aiguille de Dru, Aiguille Verte, and many other mountains in well-trodden Switzerland will occur to the reader at once.

Fig. 712.—Anticlinal and synclinal curves of the Jura Mountains.

The slopes of mountains—though to the casual observer they may appear very much the same—are very different. We sometimes find a long, easy ascent, —more usually a steepish inclination, perhaps 20°;—in other places, such as on the Matterhorn, an almost perpendicular face. Forty-five degrees rise is very steep, and 53° is the limit of any great mountain’s slope. Cliffs and precipices there are, of course; witness the terrible fall from the Matterhorn to the glacier below—thousands of feet with one tremendous leap from the rock to the ice underneath; but mountain slopes are not precipices. As a rule, we find that one side of a mountain chain is steeper than the opposite one. It is harder to climb up from Italy to Switzerland than to ascend in the opposite direction. The Pyrenees are also steeper on the south side. The Scandinavian mountains likewise are steeper in the west. The Himalaya are steepest towards the sea, so are the Ghauts. We here find a difference between the slopes of the New and Old Worlds. In the former we have the less precipitous mountain slopes towards the east; in the old world they are towards the north, and an inspection of a physical map of the world leads us to the conclusion that the Atlantic and Pacific Oceans are the boundaries of entirely different degrees of slopes. The Pacific and Indian Oceans would appear to border the more precipitous mountain sides; the Atlantic and its connections those less steep.

As a rule, we have the most elevated portions of the earth, mountains, and high tablelands, in equatorial regions; and within the torrid zone every terrestrial climate is to be found, owing to the snows of the high mountains and the heat of the valleys, which are naturally closely connected with the upheaval of mountain ranges. We have already spoken of the never-ceasing influences of the air and water upon the rocks, and we need say little about valleys. There are valleys of dislocation, denudation, and undulation. The great valley of Western Asia, wherein lie the Caspian and Aral seas, seems to have been caused by the upheaval of the Caucasus and the Persian plateau.

Plains are very varied. We have European Heaths and Landes; American Savannahs, Prairies, and Pampas; Asian Steppes, and African Deserts. All of these possess certain features in common, more or less vegetation, and sometimes absolute sterility.

Plateaus, or Tablelands, are elevated plains frequently undulating in character. The Plateau of Bolivia is 13,000 feet high, and extends along by the Andes. The tableland of Quito is nearly 10,000 feet high, and borders on the giants Cotopaxi and Chimbarazo.

Fig. 713.—The Staubbach (Lauterbrunnen).

Rivers and lakes add not only to the wealth of nations by their usefulness, but, by the additional picturesqueness of their appearance, to the beauty of the landscape. The velocity of rivers would be very much increased if it were not for the strong resistance offered by the banks and the stones to the current, and by friction. The Rhine and the Rhone, if thus unimpeded, would flow at a rate considerably over one hundred miles an hour; and our own little stream (the Thames), instead of eddying peacefully and twirling gracefully by Medmenham or Cookham, would rush along at the speed of the train which so often crosses it on its way to the sea.

The slopes of river-beds, like the slopes of mountains, vary very considerably, and the inclination of a river varies at different places; in a distance of seven hundred miles the Amazon only falls twelve feet, and the current flows chiefly by impetus already acquired. A slope of one foot in two hundred precludes all navigation, and at still greater inclines rapids and cataracts are formed—the great falls wearing away the river-bed by degrees; so it is calculated that hundreds of years ago Niagara Fall was much farther down the river, and the cataract is slowly moving up stream. In time, as the rock wears away, the height will disappear as the celebrated “Falls,” and will become a rapid within a few miles of the lake.

Lakes are derived from river-drainage and springs. Some are very salt, owing to evaporation carrying away so much water, and leaving the accumulated mineral salts. These very salt lakes are likely to dry up, as the supply of water is not equal to the demands of evaporation. Floating islands appear and disappear on many lakes. Derwentwater is one instance. On the uses of lakes and rivers it would be superfluous to dwell. We are more concerned to examine their influence on climate, and in this sense we must also consider mountains. But we will now group all the phenomena of the air and water, and their effect upon climate, under “Meteorology” in the chapters next following.

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CHAPTER XLVIII.
PHYSICAL GEOGRAPHY. METEOROLOGY.

THE ATMOSPHERE—WINDS AND AIR CURRENTS—WIND PRESSURE—STORMS—RAIN-CLOUDS—WATER-SPOUTS—ATMOSPHERICAL PHENOMENA.

Under this heading we shall find the atmosphere playing a very important part. The air is composed of oxygen and nitrogen with some carbonic acid gas and aqueous vapour. We have, under the Chemistry section, discussed these constituents which unite to make up the air or atmosphere in the following proportions:—

Oxygen	210·0
Nitrogen	775·0
Aqueous Vapour	14·2
Carbonic Acid	0·8
	1000·0

It is a fact that all over the world the same chemical result is found. Whether we bottle up the air in the valley, or, as Gay-Lussac did, go up to an elevation of 21,000 feet in a balloon, we shall find the air of the same chemical composition. In Europe, Asia, Africa, and America, it is all the same. The pressure is less as we ascend, and we cannot manage to breathe in very high altitudes so well as upon the ground for which we were fitted, but the air is the same.

The atmosphere, then, is not always equal in density, nor is it quite transparent. The light from sun and stars is, to a certain extent, lost, and it has been calculated that the sun’s rays lose one-fifth part of their brightness passing through the atmosphere. We all know what the air is. We breathe it, we feel it blowing, we witness its effects. Were it not composed as it is we should die or go mad; plants would not live, and the earth would become a desert. Air is everywhere—invisible; a so-called empty vessel is full of air because an animal will live in it till the atmosphere has become vitiated by the carbonic acid from the lungs. Yet air, or rather its watery portion, is visible when condensed.

Vapour is not perceptible. But how does it become so? We cannot see the air, how can we see a portion of it? We can answer this question by illustration. The steam from an engine is not visible on a very hot day. But when the day is damp and dull the vapour is condensed, and becomes visible; then air appears and is resolved into vapour again. This change was effected by heating water and then cooling it, when it came back to water again. This watery vapour is always present in the atmosphere. Heat, also, is present in the atmosphere, and the sun is the origin of that heat.

Fig. 714.—High tide and storm on the coast of Schleswig.

Heat, we know, is the effects of the rapid motion of small particles of matter, and is radiated from our bodies—so we feel cold; it reaches our bodies, and we feel warm. So air is heated or cooled by the sun, not in its absence, except when the earth and air have been so warmed during the day that the heat is given out by them long after sunset. We have read of the pressure of the atmosphere in the Physics section, and that warm air is lighter than cold air, as shown in the ascension of the Montgolfier balloon. It is this variation of temperature of the atmosphere that gives birth to one great meteorological agent—viz., the Wind, which we will now consider.

Winds and Air Currents.

We can easily illustrate the cause of winds. Suppose we have a hot room and a cold one, and we suddenly open the door of communication between them, the heated air which has risen to the ceiling of one room will rush out through the upper part of the opening of the door, and the cooler current will flow in just above the floor. If we place a lighted candle in the upper and lower part of the opening we shall see the flame tending outwards from the heated room, and in an opposite direction from the cold room. In the centre of the open door there will be but slight disturbance. So it is in nature. The warm air ascends, cooler air rushes in to fill the space, and a storm or a breeze is created. The balance must be restored. The upper current probably moves one way, and the lower the other way. Thus clouds are said to be “coming up against the wind” when they are moving in an upper current, or in a different direction to that the wind is blowing just above the earth’s surface.

The wind moves, with varying velocity. We have a gentle breeze when the motion of the air is about five or six miles an hour, a good breeze at twenty-five miles an hour, a high wind at thirty-five, and a gale at fifty. Hurricanes travel at sixty and seventy miles an hour, and do enormous damage. Near the Equator we do not find much wind, and this fact has caused the name of the Region of Calms, or “The Doldrums” of sailors, to be bestowed upon that portion of the globe, but this belt of calm has no fixed position. It follows the sun’s course, and is the region of greatest heat, and, as it were, the centre of a concentric circle of currents. The hot air rises and goes away; air rushes in north and south, and causes what are called the North-East and South-East Trades, or Trade Winds, owing to their being so useful in commerce for ships, or to the old meaning of the word trade, a “regular course.” The calms of the Tropic of Cancer are called the “Horse Latitudes.”

Readers of the life of Columbus will remember how his crew were affrighted at the persistency of the wind which bore him across, for no sail requires shifting, nor is a sheet altered while the vessel is making way with the “Trades.” Were the earth covered with water, we should find the trade-winds blowing equally over the surface, but the varying temperature of the land diverts them. The rarefaction of the air in the Sahara causes a westerly wind to prevail, which blows towards the land, instead of the trade wind we might expect to find.

The Monsoons, again, are caused in like manner, for the ordinary “trade” from the south-east is changed by the elevation of the heated air in Central Asia into a south-west wind, and so in the south, in consequence of the heated air from Australia, the north-west trade appears as a north-east monsoon, but is altered to a north-west wind. Nearly all the year round, therefore, we find the two winds, which are modifications of the “trades,” blowing in different directions and from different quarters. From November to March there is a north-east wind north of the Equator, and a north-west wind blows south of the Equator. From April to September a south-west wind blows at the north, and a south-east wind at the south of the line. The term monsoon signifies a “season,” and the changes of these winds give rise to tremendous storms causing great havoc.

Sea and Land breezes are really little monsoons; they are caused by the heat of the sun in just the same way, but with miniature results. We all know the sea-breeze which comes in as the land gets hot during the day, for the land warms more quickly than the sea under equally existing circumstances. So again, in the evening, the land loses its heat more quickly, and then the cool air flows out again to take the place of the warmer sea air which is continuing to ascend. The intensity and regularity varies when the degrees of heat are most different between land and sea and in tropical regions; and the varied coast formation will of course affect the wind, but as a rule the fact may be accepted as plainly explained, sea-breeze in the morning, land-breeze at night, and amateur sailors in boats at our watering-places will do well to bear this in mind.

There are a great number of local winds deriving their names from their direction or influence. We may mention them briefly. The special terms for winds are—

• The North Wind, or Tramontana.
• The North-East Wind, or Greco.
• The East Wind, or Levanter.
• The South-East Wind, or Sirocco.
• The South Wind, or Ostro.
• The South-West Wind, or Libeccio.
• The West Wind, or Ponente.
• The North-West Wind, or Maestro-Mistral.

Fig. 715.—On a lee shore.

The Mistral, or Maestrale, is well known at Nice as the north wind, while at Toulon it is a north-east wind. The other winds, such as the Sirocco, which in some places is a warm, damp wind, in Madeira is a hot wind, and likewise in Sicily, where it is equally warm and damp like steam. It has different names in various countries, such as Samiel in Turkey, and sometimes as Föhn in Switzerland, where it may, however, be a north wind—which, as all travellers know, is a dry and a hazy-weather breeze, yet sometimes moist. The Simoon is a very hot wind raising sand-storms in the deserts, and experience has shown it to be very prejudicial to life in consequence of the fine sand and the tremendous heat it carries with it. Egypt is subject to another hot wind, called the Khamsin, and the west coast of Africa is subject to the Harmattan, a dry, easterly wind. The cold, dry wind of the Himalaya is known as the Tereno. In South America there is the same wind, the Pampero blowing east and south-east. The Euroclydon, mentioned by St. Paul, is the modern bora over the Adriatic. Malta rejoices (or laments) in the Gregale, a north-east wind. There are several other terms, such as the Puna of Peru, a very drying wind; the Purgas in Labrador, the Tourmente in France, and Guxen in Switzerland. Then we have the Hurricane, from “Ouracan” of the Caribs; the Typhone, or Tae-fun of China, so called from the dreaded god Typhon of Egypt; and the Tornado—all very violent winds, and circling round, causing, so to speak, whirlwinds, by which trees are uprooted, and houses destroyed.

The measure of the velocity of wind is performed by anemometers, which record the velocity in feet per second, and the amount of pressure. The anemometer is a well-known apparatus, with its four arms terminating in “cups” and a “tablet” anemometer, which is more or less disturbed or deflected from the vertical line by each gust of wind, and thus the score of degrees is marked by an indicator, which is moved as the tablet is deflected. We annex a table of wind pressure and velocity—

Pressure of the Wind.

Velocity.		Pressure per sq. foot. Rouse and Smeaton.	Description of wind.
Miles per hour.	Feet per second.
1	1·47	0·005	Very gentle.
2	2·93	0·020
3	4·40	0·044	Light airs.
4	5·87	0·079
5	7·33	0·123	Light breeze
10	14·67	0·492
15	22·00	1·107	Brisk breeze
20	29·34	1·968
25	39·67	3·075	Strong breez
30	44·01	4·429
35	51·34	6·027	High wind.
40	58·68	7·873
45	66·01	9·963	Gale.
50	73·35	12·300
60	88·02	17·715	Heavy Gale.
80	117·36	31·490	Hurricane.
100	146·70	49·200	Tornado.

The south-west wind is more constant than any other, and the west wind in our islands is more frequent than the east; tables have been compiled showing the average number of days upon which the winds blow from different quarters, but need not be quoted. Storms can generally be anticipated by the barometer, which falls very quickly for “wind.” The quarter whence the breeze may be expected is often indicated by the streamers of clouds, or “mare’s tails,” across the sky; though we must admit the opposite direction to that anticipated by casual observers may often prove the right one.

Hurricanes and tornadoes are really whirlwinds in motion. The rotatory movement of the air is from right to left in the northern hemisphere, and from left to right in the southern—that is, in the opposite and same directions respectively as the hands of a watch move. The whirlwinds are caused by two currents of air meeting at a certain angle, just as a whirlpool is the result of opposing currents of water.

Fig. 716.—Effects of storm at Halligen in 1834.

The use of the wind in nature cannot be over-estimated. It is frequently destructive and terrible in its effects, but these comparatively trifling damages are as nothing when weighed against the advantages conferred upon mankind by the wind and the currents of the atmosphere. The north cold is tempered by the warm south wind. The pollen and the seeds of plants are borne on the wings of the wind, and the clouds are carried over the land to “drop fatness” upon our fields. The want of free circulation of air is very injurious. Witness the terrible affliction of goitre, so prevalent in the closely shut-in valleys such as the Rhone Valley, where cretinism or congenital idiotcy is distressingly prevalent.

Vapour and Clouds.

Vapour, as we have heard, is invisible, and is produced by heat. As the visible steam (which is invisible as it issues from the safety valve at the actual aperture, and nearly invisible altogether on a hot day) is produced by combustion, so vapour is produced by the heat of the sun’s rays. But there are some observations to be made respecting these rays, which are the cause of vapour, and therefore of cloud, rain, dew, frost, ice, snow, and water all over the earth; and we must look at the circumstances closely.

Those who have followed us through this volume will remember that at the end of Chapter VIII. we remarked upon the spectrum, and made a few observations respecting the heat spectrum, and the velocity of light rays, which became too rapid to be observed, and then they developed heat—invisible heat—produced by non-luminous waves, which proceed from the sun as surely as visible rays or light. Professor Tyndall has written very pleasantly upon this subject, and, with his clear leading, any reader can study for himself.

We have now arrived at the conclusion that there are visible and invisible rays giving us respectively light and heat. These latter are the means whereby the ice is melted, and by which water is evaporated to vapour, and formed into Clouds when it is chilled or condensed. Here is another link in the beautiful chain constructed by Nature. We cannot penetrate far into any portion of the system of the universe without being struck with the wondrous harmony that exists between every portion of it. Thus heat and light, vapour, cloud, rain, dew, and ice are all intimately connected.

A cloud, then, is a visible body of vapour in the atmosphere, which is supported by an invisible body of vapour. It will remain thus invisible so long as the atmosphere is not saturated with moisture. The air can contain a great quantity of moisture without its being rendered visible, and so when the day is hot we see no steam from the locomotive. It is absorbed into the dry atmosphere. But when the day is “damp” we find that the air has nearly as much moisture as it can carry, and the steam is condensed, a portion falling in tiny drops like rain. This is proved every day in cold weather when ice is found in the windows—the cold air has condensed and frozen the water breathed out from our lungs, and snow has been known to fall in a ball-room when a cold current of air was admitted.

People are sometimes apt to think that if the sun were very hot, glaciers, and such icy masses, would diminish; but we think after what has been said respecting the power of the sun’s rays to evaporate water, all will see that the contrary is the fact. Without sun-heat we should have no cloud, and as clouds give us rain and snow and ice and glacier, we must come quickly to the conclusion that glaciers and snow are the direct results of the heat of the sun. The “light” rays of the sun do not penetrate snow, and that is why our eyes are so affected in snowy regions. The poor Jeannette sufferers a short time since were blinded by reflected light, and dark spectacles are worn on all Alpine expeditions. The invisible rays, as we have said, dissolve the ice into rivers.

The atmosphere produces clouds by expansion of vapour, which chills or cools it, and it descends as rain. To prove that expansion cools air is easy by experiment, but if we have no apparatus we must make use of our mouths. In the body the breath is warm, as we can assure ourselves by opening our mouths wide and breathing upon our hands. But close the mouth and blow the same breath outwards through a very small aperture. It is in a slight degree compressed as it issues from the lips, and expanding again in the atmosphere feels colder. Air compressed into a machine and permitted to escape will form ice.

Fig. 717.—Cumulus cloud.

Water is present in clouds which assume very fantastic and beautiful forms. We know nothing more enjoyable than to sit watching the masses of cumuli on a fine afternoon. The grand masses built up like the Alps appear to be actual mountains, and yet we know they are but vapour floating in the air, and presently to meet with clouds of an opposite disposition, and produce a thunderstorm with torrents of rain. Those who will devote a few minutes every day to the steady examination of clouds, will not be disappointed. They give us all the grandeur of terrestrial scenery. Mountains, plains, white “fleecy seas,” upon which tiny cloudlets float, and low upon the imaginary yet apparent horizon, rise other clouds and mimic mountains far and farther away in never-ending distance.

A pretty, light, feathery cloud, with curling tips and fibres, is known as cirrus, and exists at a very great elevation. Gay-Lussac went up in a balloon 23,000 feet, and even at that height the cirri was far above him in space. We can readily understand that at such an extreme elevation they must be very cold, and they are supposed to consist of tiny particles of ice. Such clouds as these are very frequently observed at night, as cirro-cumulus around the moon, and a yellowish halo, apparent to all observers, is thought to be coloured by the icy particles of the lofty cirrus. The beautiful and varied phenomena of perihelia, etc., are due also to the snowy or icy flakes of the cirri and cirri-cumuli, caused by the refraction of light from the frozen particles. These cirri clouds are indicative of changeable weather as “Mares’ tail” skies, and long wisps of cloud, foretelling storm.

The cirro-cumulus is the true “mackerel” sky, and is formed by the cirri falling a little and breaking off into small pieces of cumulus, which is a summer (day) cloud generally, and appears in the beautifully massive and rounded forms so familiar. The stratus is, as its name implies, a cloudy layer formed like strata of rock. It is generally observable at night and in the winter. It often appears suddenly in the sky consequent upon diminished pressure or a rapid fall of temperature. It is low-lying cloud sometimes, and at night forms fogs.

Fig. 718.—Cirrus cloud.

The cirro-stratus is perceived in long parallel lines, and indicates rain; when made-up rows of little curved clouds it is a certain prophet of storm, and when viewed as haze is also indicative of rain or snow. “Mock-suns” and halos are often observed in the cirro-stratus.

The nimbus is the rain-cloud, or condition of a cloud in which rain falls from it. It is upon this rain-cloud we can perceive the rainbow, and on no other cloud, but otherwise only in the sky.

We have now seen the varieties of cloud and their common origin with fogs and mists, which differ from them only in the elevation at which they come into existence, according to the condition of the atmosphere.

The uses of clouds are many and varied. Their first and most apparent use seems to be the collection and distribution of rain upon the earth. But besides this, they shelter us from the too great heat of the sun, and check the evaporation at night. Supposing we had no clouds we should have no rain. If we had no rain the earth would dry up, and the globe would appear as the side of the moon appears—a waterless desert. The invisible vapour in the atmosphere will produce cloud, but the moon can have no atmosphere in that sense. Vapour will also absorb heat, and intercept the sun’s heat rays, acting much as clouds do in preventing radiation and great changes of temperature.[33]

All animals and plants depend upon moisture in the atmosphere as much as upon the varying degrees of warmth. A dry east wind effects us all prejudicially; warm, soft airs influence us again in other ways. Air will be found drier as a rule in continents than in islands or maritime districts, and this will account for the clearness of the sky in continental regions. Fogs and mists arise when the air is what is termed saturated with moisture, and colder than the earth or waters upon it. So the celebrated and dangerous fogbanks of Newfoundland arise from the warm water of the Gulf Stream, which is higher in temperature than the air already saturated. And the same effect is produced when a warm wind blows against a cold mountain; the air is cooled, and condenses in cloud.

The cooling of the breath by the exterior air is exemplified in winter when we can perceive the vapour issuing from our mouths as we speak.

Fig. 719.—Storm clouds.

Rain, Snow, and Dew.

Rain is produced by the condensation of vapour. “Vesicular vapours, or minute globules of water filled with air,” compose the clouds, and at last these vesicles form drops, and get heavy enough to come to the ground. Perhaps they are not sufficiently heavy to do so, and then they are absorbed or resolved into vapour again before they can get so far, because the lower strata of air are not yet saturated, and can therefore contain more moisture.

On the other hand, we may experience rain from a cloudless sky. This is no very uncommon case, and occurs in consequence of the disturbance of the upper strata when warm and cold currents come into collision and condense the vapours.

Rain is very unequally distributed. We shall find that the region of calms, which we mentioned in a former page, is also the zone of the greatest amount of rain. The heated air rises and falls back again, there being little or no wind to carry it away. The rainy season, therefore, sets in when a place enters the zone of calms. Equatorial districts have two rainy seasons, as they enter twice a year into the region of calms, but most places have only a wet and dry season, while north and south of the calm region we find rainless districts, or zones tempered by the trade winds, which are dry winds.

But if we suppose—as indeed is the case in South America—that these dry winds happen to come in contact with a cool mountain, the moisture of the air is precipitated in rain. In Australia, on the contrary, we have portions of land actually burnt up for want of rain, because the mountain chain breaks the clouds, so to speak, on a limited corner of the island, while the interior is parched. The winds also coming over India from the Bay of Bengal discharge clouds and rain in the Himalayan slopes. So we perceive that the situation of mountain chains have much to do with the rain-fall, and of necessity, therefore, with the vegetation and fertility of the land. This is another noticeable link in the great chain of Nature.

Fig. 720.—Meteorological Observatory, Pic du Midi.

Perhaps it may now be understood why westerly and south-westerly winds bring rain upon our islands, and why the counties such as Westmoreland and Cumberland and those in Wales receive more rain than any other part of the United Kingdom. Seathwaite, so well known to tourists in the lake district, has the proud position of the wettest place in these islands. We find that when the westerly wind sets in it has come across the warm Atlantic water and become laden with moisture, which, when chilled by the mountains, is precipitated as rain.

The amount of rain that falls in the United Kingdom is carefully measured by rain-gauges, some of which are extremely simple. The water is caught in a funnel-mouthed tube, and measured in a measuring glass every four-and-twenty hours. Thereby we can tell the annual rainfall in any given district, whether it be twenty inches or a hundred. One inch of rain actually means one hundred tons of water falling upon one acre of land. Therefore, if the annual report of rainfall (including all moisture) be twenty inches, we have an aggregate of 2,000 tons of water upon every acre of surface within the district. Twenty inches is a very low estimate. Some places have an annual rainfall of forty or fifty inches. In Cumberland we find 165 inches has been recorded! If we then multiply these last figures we get the enormous quantity of 16,500 tons of water upon every acre of land in the district in one year. It is reported from India that in the Khasia Hills the average is 610 inches, which must be the maximum rainfall in the world. At other places, in the north-west provinces, the fall is only seven inches. Sometimes in tropical rains we find fifteen inches of rain in a day, and that has been exceeded.

We can now judge of the enormous amount of moisture carried up by the sun and dispersed over the earth in rain, which swells our brooks and rivers, cleanses the air of its impurities, supplies our springs, carries with it into the sea lime from the rocks for the shells of marine animals, and then leaving its salts, is again evaporated to form clouds, which discharge the fresh water continually upon the earth in a never-ceasing rotation.

Snow.

“We all know what Snow is,” you will say, perhaps. Well, then, will any ordinary young reader tell me what he knows about snow? “It falls from the sky in white flakes,” says one. “It’s frozen rain,” remarks another. “Why, snow is snow,” says a third. “There’s nothing like it; it’s white rain-water frozen.”

Fig. 721.—Crystals of snow.

The last answer we received is the nearest of all. Snow is not snow, paradoxical as that sounds. Snow is Ice! Flakes of snow are ice-crystals—white, because reflecting light. In the section of Mineralogy we mentioned crystals, which are certain definite shapes assumed by all substances, and we gave many examples of them. Just as alum crystallizes and rock crystal assumes varied and beautiful forms, so ice crystallizes into six-rayed stars.

It is to Professor Tyndall that the world is chiefly indebted for the descriptions of snow crystals and ice flowers. In his work upon “Heat as a Mode of Motion,” this charming writer shows us the structure of ice flowers. He describes a snow shower as a “shower of frozen flowers.” “When snow is produced in calm air,” he says, “the icy particles build themselves into stellar shapes, each star possessing six rays.” We annex some drawings of snow crystals, which are, indeed, wonderfully made. Hear Professor Tyndall once again:—

“Let us imagine the eye gifted with a microscopic power sufficient to enable us to see the molecules which compose those starry crystals: to observe the solid nucleus formed and floating in the air; to see it drawing towards it its allied atoms, and these arranging themselves as if they moved to music, and ended by rendering that music concrete.” This “six-rayed star” is typical of lake ice also.

Fig. 722.—Ice crystal.

Snow sometimes reaches us in a partly melted condition; under these circumstances it is called sleet, and snow being much lighter than rain (ice is lighter than water), it descends less directly, and represents about one-tenth the depth of the rain-fall. The use of snow in warming the earth is universally acknowledged, and as it is such a bad conductor, a man in a snow hut will soon become unpleasantly warm.

Fig. 723.—Ice crystal.

Ice is only water in another form, and snow is ice; and it is the air in the snow that gives it warming properties. These are all simple facts, which any one by observation and careful reading and study may soon ascertain for himself. We have another frozen fall of water from the clouds—viz., hail, which may possibly be the development of sleet.

Hail is formed by the falling rain being frozen in its descent, or when different currents meet in the atmosphere. A hail-storm is accompanied with a rushing sound, as if the hail-stones were striking against each other. They are very destructive, and actual hail showers occur in summer more frequently than in winter, and a peculiarity noticeable with regard to hail is its infrequent occurrence during the night.

Records of destructive hail storms are plentiful. The hail assumes a great size, weighing sometimes as much as two ounces, and measuring several inches round. Thunder and lightning are very frequent accompaniments of hail showers.

Dew is moisture of the atmosphere deposited on a cool surface—another form of condensation, in fact. Cold water in a tumbler will produce a “dew” upon the outside of the glass when carried into a warm atmosphere. Such is the dew upon the grass. It is produced by the air depositing moisture as it becomes colder after a warm day when much vapour was absorbed. Warm air can hold more water than cold air, and, the saturation point being reached, the excess falls as dew at the dew (or saturation) point. We have previously remarked that one use of clouds was to prevent rapid radiation of heat which they keep below. Under these circumstances—viz., when a night is cloudy—we shall find much less dew upon the grass than when a night has been quite clear, because the heat has left the atmosphere for the higher regions, and has then been kept down by the clouds; but on a clear night the air has become cooled rapidly by radiation, and having arrived at saturation point, condensation takes place.

Dew does not fall, it is deposited; and may be more or less according to circumstances, for shelter impedes the radiation, and some objects radiate less heat than others. Hence some objects will be covered with dew and others scarcely wetted.

When the temperature of the air is very low,—down to freezing point,—the particles of moisture become frozen, and appear as hoar-frost upon the ground. Thus dew and hoar-frost are the same thing under different atmospheric conditions, as are water and ice and vapour.

We have now come round again almost to whence we started. We have seen the land and water, and the parts that water, in its various forms, plays upon the land, and its effects in the air as rain, etc. We have noticed the winds and air currents as well as the ocean and its currents. We know what becomes of rain and how it is produced, and how the sea works upon the shore, and how clouds benefit us. There are besides some less common phenomena which we will now proceed to examine.

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CHAPTER XLIX.
PHYSICAL GEOGRAPHY. METEOROLOGY (continued).

ATMOSPHERIC PHENOMENA—THUNDER AND LIGHTNING—AURORA BOREALIS—THE RAINBOW—MOCK SUNS AND MOCK-MOONS—HALOS—FATA MORGANA—REFLECTION AND REFRACTION—MIRAGE—SPECTRE OF THE BROCKEN.

There are a great number of interesting, and to inhabitants of these islands uncommon,—perhaps we might say fortunately uncommon,—phenomena, which overtake the traveller in other countries. We have referred to whirlwinds and tornados, and will now mention two phenomena connected with these storms. There is the water-spout, for instance, and sand-pillars in the desert, which are whirled up by these winds in spiral columns of water and sand respectively. The tiny whirlwind at cross-roads, which picks up straws and leaves, is the common appearance of whirling or crossing currents of air.

Fig. 724.—The Waterspout.

Waterspouts, when they are permitted to come near a ship at sea, or when they break upon land, which is seldom, are very destructive. The waterspout is begun generally by the agitation of the sea, and the cloud above drops to meet the water, which at last unites with it, and then the column of whirling liquid, tremendously disturbed at the base, advances with the prevailing wind. Its course is frequently changed, and ships within its influence would be speedily wrecked. The only way to save the vessel is to fire a cannon ball through the column and break it.

Fig. 725.—Thunderstorm and shower of ashes from Vesuvius.

A waterspout once devastated a district in the Hartz mountains of Saxony. “A long tube of vapour descended to the earth, and several times was drawn upward again; but at last it reached the ground, and travelled along at the rate of four-and-a-half miles in eight minutes, destroying everything in its way.”

On another occasion at Carcassonne in 1826, “a reddish column was seen descending to the ground, and a young man was caught up by it and dashed against a rock.” His death was instantaneous.

The cause of these whirling winds is supposed to be in the action of vertical currents of air which ascend heated, and return rapidly as cold air. The “waterspouts,” etc., are quickly formed. The tornado is a monster whirlwind like a waterspout in form, and advances at a tremendous rate—eastward as a rule. It moves in leaps and bounds, passing over some portions of the ground and descending again. The current of air is directed to the centre; the cyclone, as mentioned, has a spiral or rotatory movement.

Thunder and lightning have been, to some extent, described under the head of Electricity, but some observations may also be introduced here, as storms of that nature appertain to meteorology distinctly.

Electricity is always present in the atmosphere, and arises from evaporation and condensation as well as from plants. As the air becomes moist, the intensity of the so-called “fluid” increases, and more in winter than in summer. Clear skies are positively electric, and when large, heavy clouds are perceived in process of formation in a sky up to that time clear, a storm is almost certain to follow. These “thunder clouds,” in which a quantity of electricity exists, attract or repel each other respectively. The cloud attracts the opposite kind of electricity to that within it; and when at last a tremendous amount has been stored up in the cloud and in the air, or in another cloud, the different kinds seek each other, and lightning is the result, accompanied by a reverberation and commotion of the air strata, called thunder.

Lightning most frequently darts from cloud to cloud, but often strikes the ground, whereon and in which are good conductors, such as wet trees, metals, running water, etc. The “electric fluid” assumes different forms—“forked,” “sheet,” and “globular.” The second is perhaps the most familiar to us, and the third kind is the least known of all. There are many well-authenticated instances on record in which lightning with the form and appearance of fireballs has entered or struck houses and ships.

“Fulgarites” are vitreous tubes formed in sandy soils by the lightning in search of subterranean water-courses, for running water is a great conductor of electricity.[34] The fire-ball form of lightning has been known to enter a school-house where a number of children were, and to singe the garments of some, killing others. The ball passed out through a pane of glass, in which it bored a hole, breaking every other pane, however, in its transit. Another instance occurred in which the lightning ran about the floor of a room, and descending the stairs, exploded without doing any injury.

Lightning, like the electric current of the laboratory, will not always set fire even to inflammable objects. An electric spark can be passed through gunpowder without setting fire to it, and lightning will often shatter the object without firing it. Death by lightning is instantaneous, and in all probability quite painless; for we may argue from analogy, that as those who have been rendered insensible by lightning have had no remembrance of seeing the flash which strikes so instantaneously, nor of hearing thunder after it, it is instantaneous in its effects. Besides, the natural attitude is preserved, and the face is usually peaceful and limbs uncontorted after death by lightning.

There are some curious electrical phenomena, such as St. Elmo’s Fire, already noticed under Electricity; and in some parts of America, in very hot weather, such a light is perceived to issue from trees as the fire glides through the forest. Many instances are on record concerning the luminosity of pointed sticks, and even of the tails and manes of horses in certain conditions of the atmosphere, and of the universal power of electricity and its pervading influence in nature. The benefits conferred by thunderstorms in purifying the air, and in the production of ozone and nitric acid, are very great, and apart from the magnificent phenomena exhibited, are well worth our attention, though beyond our reach.

Fig. 726.—Aurora Borealis.

Terrestrial magnetism, however, is still more puzzling in its action than is electricity, and the study of the needle, its destination, inclination, and intensity, which are marked upon charts, just as are the weather reports of the Times, is an interesting one. These magnetic maps are termed the charts of Isoclinic and Isodynamic lines. The declination of the magnetic needle from the true north is its deviation from that point, and the “inclination” is its dip towards the horizon. The line of its direction being known as the magnetic meridian, its divergence from this line constitutes its declination. There are places where it does not deviate, and these, in direction north and south, are called lines of “no variation.” There are also places in the equatorial regions where the needle does not “dip.” The line connecting such places is termed the Magnetic Equator, and north or south of this the needle dips respectively to north or south in degrees coinciding with the distance from the equator.

The earth, then, acts as a magnet, and attracts the needle, but the magnetic poles are not identical with the terrestrial poles. The north magnetic pole was reached in 1831 by Sir James Ross, when the dip was only one minute less than 90°, and the south magnetic pole was very nearly reached also by him in 1840. The magnetic equator passes between these two points.

Fig. 727.—Paraselenæ, or mock moons.

It is to magnetic atmospherical disturbance that the aurora is due. These northern (or southern) phenomena are extremely brilliant and diversified. In temperate regions the aurora does not present such grand forms as in the extreme north. There the spectacle is astonishingly beautiful. The sky at first clouds over, and mist is developed. Humboldt has eloquently described the aurora borealis, and the beautiful changes of light, the constant movement, flashes, etc., denoting a “magnetic” storm, as electrical discharges indicate an electric storm, although the area affected by the former is far more extensive than that of the latter, and there is no thunder accompanying the magnetic storm, with the production of which the electricity of the earth is unassociated. To the continuous flow of this electricity the aurora is due, and the flashes are only the electric current descending towards the earth. But the true reason of the phenomena may have to be yet discovered, for nothing absolutely certain is known as to the origin of the aurora.

Amongst the numerous effects of refraction and reflection of light the Rainbow is most common and the most beautiful. If we hold a chandelier “drop” in the sunlight, we shall see a brilliant representation of the rainbow on the wall or on the carpet. The three colours—red, yellow, and blue—mingle or shade away into seven—red, orange, green, blue, yellow, indigo, and violet. These colours are all found in the rainbow.

Fig. 728.—Parhelia, or mock suns.

The colour of the atmosphere—the usual blue tint of the sky—arises from the blue rays of the spectrum being reflected more than the rest by the aerial particles, and the less vapour the bluer the sky, because the vapour gives it a whitish or misty tint. At sunset and sunrise the sky is red or yellow, like gold, or of crimson hue. This is because the sun’s rays have so much farther to come to us at sunrise or sunset, as you will readily perceive if you draw a line from the sun to the sides and then to the top of the arc of the heavens. The blue rays are thus lost in space, while red and yellow, which travel so much faster than blue, are transmitted to the eye, not giving the air time to absorb them.

If you go under water and look at the sun it will appear very fiery indeed, and we may likewise imagine that fiery crimson rays, which betoken atmospherical disturbance, very often are due to the moisture through which they are transmitted. Wet and storm frequently succeed a crimson sunset, which betokens much moisture in the air. The sun is similarly seen through the steam issuing from an engine, and the colours vary according to the density of the steam in its stages of condensation.

Fig. 729.—Mirage at sea.

Vapour, we know, is invisible and transparent, but when it has been condensed into rain-drops, and the sun is shining, if we stand with our backs to the sun we see what we call the rainbow, because a ray of light entering the drop is reflected, and as all rays are not of equal refrangibility, the light, which is composed of three simple rays, is divided and reflected into those and the complementary colours. When the sun is at the horizon, the rainbow, to an observer on the earth (but not on a mountain), will appear to be a semi-circle. The higher the sun rises the lower is the centre of the rainbow. So we can never see rainbows at noon in summer because the sun is too high. A second rainbow is not uncommon, the second reflection producing the colours in a different order. The colours in the “original” range from violet to red; in the “copy” they extend from red to violet. “Rainbows” are often visible in the spray of waterfalls and fountains.

Halos are frequently observed surrounding the moon, and then we are apt to prognosticate rain.

“The nearer the wane

The farther the rain,”

is an old couplet referring to the appearance of the moon, and is supposed to foreshadow the weather by the size of the halo, which is caused, as we know, by the existence of vesicular vapour in the atmosphere.

Mock Suns, or parhelia, and mock-moons, or paraselenæ, are continually observed in cold climates, where the tiny ice particles are so abundant in the air. These phenomena were recognized by the ancients, and halos round the sun can be observed by means of darkened glasses. We annex an illustration of a mock sun and moon seen on the continent of Europe. Readers of Mr. Whymper’s “Scrambles in the Alps” will remember the gorgeous, and to the guides mysterious, fog-bow or sun-bow seen as the survivors of the first and most fatal ascent of the Matterhorn in 1865 were tremblingly pursuing their descent over the upper rocks of that mountain.

The Mirage, or Fata Morgana, is a very curious but sufficiently common phenomena, and in the Asiatic and African plains it is frequently observed. When the weather is calm and the ground hot, the Egyptian landscape appears like a lake, and the houses look like islands in the midst of a widely-spreading expanse of water. This causes the mirage, which is the result of evaporation, while the different temperatures of the air strata cause an unequal reflection and refraction of light, which give rise to the mirage. Travellers are frequently deceived, but the camels will not quicken their usual pace until they scent water.

The Fata Morgana and the inverted images of ships seen at sea are not uncommon on European coasts. Between Sicily and Italy this effect is seen in the Sea of Reggio with fine effect. Palaces, towers, fertile plains, with cattle grazing on them, are seen, with many other terrestrial objects, upon the sea—the palaces of the Fairy Morgana. The inverted images of ships are frequently perceived as shown in the illustration (fig. 729), and many most extraordinary but perfectly authentic tales have been related concerning the reflection and refraction of persons and objects in the sky and on land, when no human beings nor any of the actual objects were within the range of vision.

It will be well to explain this phenomenon, and the diagrams will materially assist us in so doing, for the appearances are certainly startling when realized for the first time. The Spectre of the Brocken we see mimics our movements, and we can understand it. But when apparently solid buildings appear where no buildings have been erected,—when we see—as has been perceived—soldiers riding across a mountain by a path, or ledge, perfectly inaccessible to human beings even on foot, we hesitate, and think there is something uncanny in the sight. Let us now endeavour to explain the mirage.

Suppose that in the annexed diagram the space enclosed between the letters A, B, C, D, be a glass vessel full of water. The ship is below the horizon, the eye being situated at E—the glass vessel of course representing the atmosphere charged with moisture. The eye at E will perceive the top of the mast of the ship, S, and we may imagine a line drawn from E to S. Then put a (short focus) convex lens at a just above this (imaginary) line, and a concave one, b, just over it. Through the former an inverted ship will be seen, and an erect one through the latter at S′ and S″ respectively. We now have the effect in the air just as reproduced in nature by the difference in temperature in air strata, which cause it to act like a concave lens when the density of the water diminishes towards the centre, and like a convex lens when it is increased.

Fig. 730.—Explanation of Mirage.

This can be proved by heating the air (by hot irons) above the glass vessel filled with oil, and the effects will be just the same as through the lenses. Dr. Wollaston obtained the mirage by using a clear syrup,—about one-third of the vessel full,—and filling it with water. The gradual mingling of these fluids will produce the phenomenon. The illustration in the margin (fig. 731) shows us the rays proceeding from the ship’s hull, and refracted into the line reaching the eye, above the line proceeding from the mast, so the ship appears hull uppermost; the rays cross at x. But if they did not cross before they reach the eye, the image would appear as at s´ p´ in an erect position.

Fig. 731.—The Mirage.

The Spectre of the Brocken arises from a different cause. Such appearances are only shadows,—projected on thin clouds or dense vapours at sunrise, or when the sun’s rays are directed horizontally,—for of course vertical rays will throw the shadow on the ground on to the zenith. Balloons are also reflected thus, and much interest has been caused by the appearance of a twin balloon, until the aerial voyagers have discovered the cheat by seeing the shadowy aeronaut imitating their actions, and the second balloon has been discovered to be an airy nothing.

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CHAPTER L.
PHYSICAL GEOGRAPHY. CLIMATOLOGY.

WEATHER, CLIMATE, AND TEMPERATURE—ISOTHERMAL LINES—ISOBARS, WEATHER FORECASTS, AND SIGNS OF THE SKY.

It is usually considered a sign of a paucity of ideas when one begins a conversation about the “weather,” but there can be no doubt that there is no more interesting question in social life at certain times as to whether it will or will not rain. Our outdoor amusements are all dependent upon weather, and a little cloud may throw a deep shadow over all our pleasure if we neglect to bring out an umbrella, or to carry a waterproof. We are never independent of what we term the “capricious” climate, but in reality the laws of “the Weather,” though so imperfectly understood, are fixed and invariable, and if we could read the signs in the sky and learn the condition of the atmosphere, we might leave the “prayers for rain” and “for fine weather” out of the Church service, for then we should understand that unless miracles are performed for us the laws of Nature can in no wise be altered.

Of late years weather forecasts (not prophecies) have come before us in our newspapers after the manner instituted by the late Admiral Fitzroy, whose name has become a household word in England. But at the commencement of the Christian era and before that time the signs of the heavens and the behaviour of animals and birds were noted with reference to changes of weather. If we read Virgil we shall find numerous references to these portents, and the translation usually quoted will furnish us with information which must be as true nowadays as it was in Virgil’s time, for wild animals do not change their habits. Speaking of wet weather in the Georgics the poet wrote:—

“The wary crane foresees it first, and sails

Above the storm, and leaves the hollow vales;

The cow looks up, and from afar can find

The change of heaven, and sniffs it in the wind;

The swallow skims the river’s watery face,

The frogs renew the croaks of their loquacious race;

The careful ant her secret cell forsakes,

And draws her eggs along the narrow tracks;

Huge flocks of rising rooks forsake their food,

And, crying, seek the shelter of the wood.

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The owls, that mark the setting sun, declare

A starlight evening and a morning fair.”

We might quote further selections respecting the signs in the heaven and earth mentioned, but the foregoing verses will be sufficient to illustrate our position, and to show us that weather forecasting is, at any rate, as old as the Christian era.

The moon is generally supposed to influence the weather—a “Saturday’s Moon” being particularly objectionable, or when she appears anew at some hours after midnight thus—

“When first the moon appears, if then she shrouds

Her silver crescent, tipped with sable clouds,

Conclude she bodes a tempest on the main,

And brews for fields impetuous floods of rain.”

Fig. 732.—In the northern Seas.

Weather permitting, we can go out and study the clouds as described in the foregoing chapters, or consult the barometer, and see which way the wind blows. The child will tell us that a high “glass” means fine weather, and a low barometer indicates rain, but this is only relatively true. A high glass may be falling, a low glass may be rising. A sudden fall or a sudden rise are indicative of bad, windy weather, or a short-lived fine period. The glass may rise with a northerly wind, and rain will supervene, so careful observation is necessary before one can obtain even a superficial knowledge of the weather. (See subsequent observations on “Weather.”)

The Americans telegraph the results of their observations of coming storms across the Continent, corrected by the signs noticed and recorded by vessels arriving in New York. Thus they are frequently very accurate; steady application and observation at Sandy Hook must give them a great deal of useful information for the “forecasts.”

The word Climate is derived from the Greek klima, a slope; and thus at a glance we perceive how the aspect it presents to the rays of the sun in the earth’s revolutions, must affect the “climate” of a country. Of course the position of any portion, the elevation and locality of the mountains, have also a share with the soil, winds, rains, and sea-board, in determining the climate of any region. Many points have already been touched upon in former chapters. Temperature, moisture, and vegetation are the chief natural features which determine climate, and we must find out the position of the land with reference to the sun first, to ascertain the climate.

The more vertical the sun is the hotter the atmosphere, for the rays strike directly upon the earth, which radiates the warmth received. These heat rays are, as we know, invisible. The hottest portion of the earth must be at the equator for the sun is overhead, and the rays beat down directly upon the earth. The sun is also nearer than when at the horizon, and less rays are absorbed by the atmosphere. The longer the day the greater the heat.

Fig. 733.—In the southern steppes.

Temperature is registered by observation of the thermometer, and the distribution of heat is represented upon a chart across which lines are drawn at places of equal temperature. These lines are called “isothermal.” There are also terms to denote equal winter temperature and the average summer heat—isochimines and isotheres respectively.

Temperature decreases as we ascend from, and increases as we descend into, the earth. This fact proves that the air is not warmed by the sun’s heat, but by radiation from the ground. As we ascend we reach the line of perpetual snow, which varies in different parts of the globe. In the tropics it extends from 15,000 to 18,000 feet; but it varies even in places of the same latitude, according as the towns are inland or on the coast, as in the Pyrenees and Caucasus, where there is a difference of three thousand feet in the snow limit.

The line of the snow limit, as a rule, gets lower as we journey from the equator to the poles. Exception will be found in the Himâlaya, where the snow line is higher on the northern side, in consequence of the existence of the Thibetan tableland, which causes a higher temperature than that existing upon the abrupt southern slope. Countries, therefore, though in the same latitude, may have different climates according to the elevation of the land.

The proximity to the sea is another reason for climatic difference. Water takes some time to become warm, but when it has once become so it will not readily part with its heat. The Gulf Stream, with its warm current beating along our shores, gives us a high temperature and a moist climate—a very different condition to Newfoundland or Nova Scotia, which are in much the same latitude as England and Ireland. By the sea the climate is more uniform, and the extremes of heat and cold are not so distant. We send invalids to the seaside to save them the effects of such violent changes. Winters are milder and summers cooler by the sea.

We can readily understand how such circumstances affect the vegetation, and places which in winter may enjoy a mild and genial climate (comparatively speaking), may have a cold summer. Ferns may flourish in winter out of doors, but wheat will not ripen in the autumn owing to the want of heat.

The winds also, and the soil and aspect of a region, all have a share in determining its climate. Trees bring rain by evaporation, and a wooded country is a blessing to its inhabitants, defending their habitations from wind and avalanches in mountainous districts. But the climatic conditions are altering. The ground is being more and more cleared; the soil is more cultivated, and moisture is being more eliminated from it. Therefore the air becomes warmer by the radiation of the ground, and clouds are formed which keep the warm layers down nearer the earth. Mountains, as we have seen, affect the rain-fall in districts; and in Scandinavia—in Norway chiefly—the average rain-fall is very high. The sheltering effects of mountains from east or northerly winds also alter the climate, while clay or gravel soils are cold or warm inasmuch as they absorb, or evaporate, moisture. Some surfaces being different from others give out more heat.

In some mountainous districts we shall find every variety of climate from the sea-level tropical heat to the rigours of the pole. The greatest average temperature is north of the equator in Africa; the lowest in the north, to the west of Greenland. Masses of land act in a different manner to the oceans, and the former become heated and cooled with equal rapidity, while the sea, as already mentioned, is slow to lose its heat. Our land enjoys a mild and equable climate as a rule, because it is surrounded by water, and the Gulf Stream warms it. The European climate, taken altogether, may be considered the best on the globe.

We will now pass on to a few observations concerning the weather, and the means of determining it beforehand.

It is always a dangerous thing to act the part of a prophet, and the uncertainty attending an uninspired foreteller’s predictions must in time disparage him in the estimation of his hearers and disciples. But there are signs in the sky which we can discern and render valuable by the aid of instruments. We must have a reliable barometer and thermometer, and keep a record of the average conditions of the weather, if we wish to wear the mantle of the weather-prophet—a term now, in America, applied (jokingly, no doubt) to people who are not particular in their statements of facts.

But without entering upon any scientific discussion, we may state a few plain rules which can be observed, besides the indications of a rising or falling barometer. Having frequently studied the aspects of the clouds, with the assistance of the hints from the wind-currents, we can fairly prognosticate or suggest probable changes of weather.

Fig. 734.—Weather chart.

We have already remarked upon the colours of the sunset, which are attributable to the vapours in the atmosphere, and we say a red sky foretells fine weather; a yellow sky changing into green means rain, or rain and wind; on the other hand, when the red rays appear we may anticipate fine weather, as the atmosphere is becoming less and less moist.

A “low” dawn is known as a good sign; so when the first rays appear at, or near the horizon, we may anticipate a fine day, as we may when the morning is grey.

“Evening red and morning grey”

are almost unfailing tokens of fine weather.

Very often a yellow sunset means wind; a wild, crimson sky means a gale. On the afternoon (Saturday) before the Eurydice foundered off the Isle of Wight, we particularly noted the sunset at Gravesend; and it was evident (in our estimation) that a sudden storm was imminent, and we remarked it to our companions. The sudden fall of the barometer, and the appearance of the rising clouds early on that sad Sunday afternoon, approaching in dark masses from the west and north-west, spoke of rain and (possibly) snow. How true the forecast was the event proved.

When clouds are soft and thin we expect fine weather; when they are dark and hard, rain and wind. A ragged-edged and heavy cloud indicates thunder and lightning, with squalls when we see dark clouds flying rapidly across the mass of cumuli. A “mackerel” sky and “mares’ tails” generally foretell wind, the direction and the upper currents being noted. The longer the warning given by the heavens, the longer the bad (or fine) weather will last; and the converse is also true.

“Evening grey and morning red,

Put on your hat, you’ll wet your head.”

The cirrus is a wispy cloud, and is often observed extending across the sky on a fine afternoon. This may or may not indicate rain; it generally points to wind. If its direction be northerly and west to southerly and east, it is a good sign, but from west to east it is a bad sign. The habits of birds and animals, and their anxiety for shelter, “pigs running with pieces of straw in their mouths,” and the low-flying swallow, are all signs of approaching rain and bad weather, and the scintillation of stars betokens moisture in the atmosphere. These are well-known appearances, but there are others regarding the winds and currents of air which require the assistance of Admiral Fitzroy’s book.

For instance, a falling barometer with rising temperature means southerly winds and rain; in winter, with low temperature, snow.

But a rising barometer with northerly wind often means rain.

A rising glass after a low fall may, and often does, indicate more wind from the north, and after that fine weather, if lower temperature also supervene. If warm weather continue under the circumstances, the wind may back and blow from the southward.

“The most dangerous shifts of wind happen soon after the barometer rises from a very low point, or if the wind veers gradually shortly after with a rising barometer.”

If the barometer rises with a southerly wind fine weather may be expected, and if it falls with a northerly wind rain, hail, and snow are imminent, for the rule is a fall for southerly, and a rise for northerly winds.

A sudden fall with west wind indicates storm from northerly quarters (N.E. to N.W.). An east gale veering southwards with falling glass indicates a change of storm-direction to a point from N.W. or N.E., suddenly and violently, though a change might have been expected from the appearance of the glass. A calm frequently occurs between these disturbances.

A backing wind—that is, a wind going in a direction opposed to the sun’s course (and with the earth)—is a bad sign after unsettled weather. The wind is said to “veer” when it goes with the sun.

The south-east wind, with clear sky, warm weather, and low clouds on the horizon, is a sign of wet. A dry east wind means fine weather. Heavy clouds in the north-west generally bring a thunderstorm. When really distant objects look very near rain must be expected.

There are many exceptions to weather rules, and none can be laid down as invariable. The ever-changing currents of air, and varying moisture of the atmosphere, give rise to barometric changes, which should be carefully noted. A little experience and close observation for one year, with notes of signs, and indications of temperature, will assist any one to tell the probable change that is approaching.

There are a great number of signs of weather which are observable in the animal and even in the vegetable kingdom, as well as in the moon and stars. Many flowers close their petals before rain comes on, and the behaviour of domestic animals often foretells storm. Sheep huddling together in a corner tell us the direction from which the tempest is approaching; sea birds fly to shore, and land birds become restless.

The naturalist will observe the domestic animals which become uncomfortable and sniff the air; the cat lies with her head down, the brain lowest; and frequently washes her face, or scampers about aimlessly. Spiders disappear, and worms come up to seek the expected water. When fine weather is coming all nature appears glad, but leeches sink into the water as far as they can.

The above are some of the domestic and common signs of coming rain, and conversely for fine weather. A wailing wind, a cloudy mountain, a greenish rainbow or too red a one, a pale moon with indistinct points, or a halo round it, are all signs of rain and possibly wind. So the most superficial observer may with these few suggestions inform himself of the chances of fine or wet weather.

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CHAPTER LI.
BIOLOGY. PART I. BOTANY.

PLANTS AND ANIMALS—STRUCTURE OF PLANTS—FLOWERING PLANTS—THE STEM—THE LEAVES—FORMS OF LEAVES.

Biology is derived from the Greek word Bios, “life,” and logein, “to speak,” and constitutes the science of Organic Life. This science is divided into two branches: Botany, relating to the life of plants; Zoology, to the animals.

Plants, then, are living things, and as we proceed we shall find them born, or “germinating,” growing up as young plants, maturing as adults, and finally dying, and their particles resolving into their elements. There is more than one application of the text, “Man is but as a flower of the field.”

In the Geological section we noticed the progressive stages of the vegetable creation, and if we turn back to those pages wherein the various epochs of the earth’s formation are enumerated, we shall see how plant-life developed. Thus we find in the Cambrian the first traces of vegetable life in the weeds of primeval seas. The Silurian strata and the Devonian furnish us with many fossils of marine algæ, and if we examine the succeeding periods we shall find a progressive increase and development; pines and tree-ferns in the sandstone, and most of the plants (by which term we include all varieties) were different from those at present existing in the earth.

Fig. 735.—Branch of the oak.

We spoke of climate lately, and referred to the vegetation having an influence upon it. The same is true of the effect of climate upon vegetation. The conditions of plant-life depend upon climate, as it partly depends upon plant-life. But of all the necessary conditions the first created thing is the most necessary—light. Without light the plant is nothing.

Fig. 736.—The pine.

Plants have many points of similarity with animals. They live, they possess organs, their compositions contain similar substances, such as carbon and albumen, and close chemical analyses have found the existence of the elements oxygen, nitrogen, hydrogen, and carbon in animals and plants. Therefore water must play a conspicuous part in all. Professor Huxley puts this question in his usual clear fashion. He says:—

“It is a very remarkable fact that not only are such substances as albumen, gluten, fibrin, and syntonin known exclusively as products of animal and vegetable bodies, but that every animal and every plant at all periods of its existence contains one or other of them, though in other respects the composition of living bodies may vary indefinitely. Thus some plants contain neither starch nor cellulose, though these substances are found in some animals; while many animals contain no horny matter and no gelatine-yielding substance. So that the matter which appears to be the essential foundation of both the animal and the plant, is the proteid united with water, though it is probable that in all animals and plants these are associated with more or less fatty and amyloid (starchy and saccharine) substances, and with very small quantities of certain mineral bodies, of which the most important appear to be phosphorus, iron, lime, and potash. Thus there is a substance composed of water, plus proteids, plus fat, plus amyloids, plus mineral matters, which are found in all animals and plants. When these are alive this substance is termed Protoplasm.”

Fig. 737.—The fir.

We have taken the liberty to extract the above paragraph, as it expresses in a few words, and very clearly, the common origin of plants and animals. We will now consider the conditions of plant life. Heat, light, and moisture are the principal necessaries, with of course air and certain earthy matter. Some plants, like some few animals, live in darkness, such as truffles and fungi, as do cave-fish and bats. But this is the exception, and the sense in which plants (or animals) can exist without light is a very restricted one, and only to be sustained at the expense of the plant material, which must originally have been derived by the action of light. Light, therefore, is the great “producer.” It gives life to plants upon which animals feed, and therefore light is in one sense the beginning of all things. We can now understand why light must have been created first.

Many interesting experiments can be made to observe the effect of darkness and different coloured light (transmitted through coloured glasses) upon plants; and it will be observed that although the leaves may not develop the natural green tint, the flowers will exhibit their usual colour. One effect of light upon plants is to make them green.

We all admire the beautiful green of the spring leaves, and the freshness of the colours of the trees and grass. But if we pluck up a plant its root is not green. Why then is the cleaned root not as green as the upper portion?—Because of the absence of light. There is a substance called Chlorophyl which, when acted upon by light, becomes green. This is contained in plants, and when the daylight falls upon it the substance turns green. So, as we said above, plants are not green when kept in the dark. Celery is a common instance. Heat, of course, has much to do with the activity or vitality of plants, and the range extends from just above freezing point to 122° Fahr. We find tiny plants blossoming in Alpine regions close to the snow, and others in full life in the tropics, protected from the fierce rays by scaly coverings and huge leaves. In the northern regions buds appear as soon as the surface warmth is felt, and even when no heat can yet penetrate to the roots. Thus we see that Nature fits the animal and the plant to the localities in which they live, and they exist interdependently. Some can defy cold, others flourish in drought; some love moisture, others live in great heat encased in prickly armour.

Fig. 738.—Branch of elm.

With this introduction to biology we may now pass on to speak of the seeds and germination of plants, which we divide into the flowering and non-flowering species. We suppose that the appearance of various organs of plants are familiar to our readers, and the root, the stem, the leaves, and the flower itself, as well as the seeds, are well known, and their uses understood generally.

Now if we compare a mineral—say a crystal of quartz—with a plant, we find the crystal uniform, consisting of small particles of quartz throughout, and it appears an aggregation from outside of these particles in a particular form. It cannot grow from within. But a plant can; and it is very different in structure and appearance. It receives nourishment from outside also, but it assimilates the materials, which are not the same as those we meet with in the plant itself. The mineral, on the contrary, is essentially the same throughout; it can only grow by aggregation of atoms like itself. A plant, therefore, like an animal, must have organs within it, and must be capable of change in itself; it has powers of reproduction, and in some few instances of locomotion; it can eat flies, and assimilate them as an animal does.

A plant, therefore, is an organized body without external voluntary movement; and hereby it is essentially distinct from an animal, with which, in organization, it is closely connected. The simplest form of the animal as of the plant, is that of a minute vesicle or cell, containing a fluid in which are some granular substances. At this stage it could not be distinguished from the simplest plant, if it had not the faculty of voluntary movement—the power of changing its place. The animal has a locomotive power. Sometimes, indeed, it is a very limited sphere to which it is confined; yet it may change its place for another more conducive to the exigencies of its being.

It is sufficient for the present to have given the most general characteristics by which plants are distinguished from the other objects that, with them, compose the great kingdom of Nature. A precise and clear apprehension of their varied forms and wonderful phenomena can only be obtained by a careful analysis of the nature and structure of the subjects of the vegetable kingdom.

The cell is the fundamental or elementary organ of plants, and the knowledge of its metamorphoses and functions constitutes the foundation of botany. We must therefore first consider the simple organs of plants.

Structure of Plants.

It will be necessary for the reader to gain some little knowledge of the tissues and cells of plants before he proceeds to examine the organs of development, and a microscopic examination will soon disclose the few simple tissues which are termed cells and vessels. These exist in all plants of whatever nature. Plants are aggregations of cells, “every one of which has its little particle of protoplasm enclosed by a casing of the substance called cellulose, a non-nitrogenous substance nearly allied in chemical composition to starch.”[35] The tissues are “cellular” and “vascular” respectively.

The cells have an outer sac or covering which is transparent, and this cover is the cellulose above mentioned. It contains (1) the protoplasm, a kind of jelly-like substance (which holds the proteine or basis of life); (2) water or cell-sap; (3) the nucleus; and (4) chlorophyl. This protoplasm is apparent in both plants and animals. The cells containing these various substances—in which we find oxygen, hydrogen, nitrogen, sulphur, and carbon, with phosphorus perhaps—are divided to form new cells, and so on with most astonishing rapidity, amounting in some instances to millions in a day, and a case of this nature will readily be recognized in the mushroom.

A B C
Fig. 739.—Plant cells.

Cellular tissue is composed of these cells, and vascular tissue is composed of vessels or tubes like coiled springs, which are cells without divisions or partitions. These tissues will be referred to farther on as dotted ducts or tubes.

Fig. 740—Form of cells.

In most of the spongy parts of plants, as in the pulp of fruits and pith of elder, the cells preserve the globular or oval shape represented in fig. 739 A. But the cells, in consequence of that mutual pressure, more frequently assume the form of a polygon (fig. 739 B), the section of which is generally hexagonal. The cellular tissue may generally be compared to the bubbles produced by blowing through a straw or tobacco-pipe into soap and water; or it may be illustrated by placing balls of moist clay together, and then pressing them more or less strongly. In this manner every individual ball assumes a polygonal shape corresponding to the form of the cells represented in fig. 739 C, and which disposition is, in many plants, preserved with the utmost regularity. Such cells as are, with tolerable equality, extended in all directions, are named parenchyma, and of these are composed the tuberous parts of plants, as the potato, dahlia-roots, etc., and especially the soft, spongy parts of the pith, bark, leaves, etc. We frequently, however, meet with cells which are extended longitudinally, and pointed at both extremities, as in fig. 740. The sections of these cells, which are compactly arranged, have the appearance of a hexagon. They are termed woody cells, or woody tissue (prosenchyma), and constitute the chief portions of the more solid parts of plants, as the ligneous parts of trees, shrubs, etc. Very long, flexible cells, as those which constitute the fibres of flax and hemp, are called bast-cells, and appear under the microscope as round threads of uniform thickness, whereas the fibres of cotton wool, which rarely exceed one or two inches in length, when magnified, present the appearance of flattish bands with somewhat rounded margins. By these marks, the union of flax and cotton in the same web or piece of cloth may be detected.

Occasionally the cells assume very abnormal shapes, as the stellate or star-formed cells. These are described as irregular cells.

Fig. 741.—Vascular tissue.

As every plant, whether small or great, is only an aggregate of a great number of cells, so, also, the life of a plant is nothing else but the sum of the activities of all the cells of which it is composed. The special province of the cells is to receive from the soil or atmosphere the water necessary for the various vegetative purposes, together with the nutritious materials dissolved in the watery and aerial fluids, and to circulate them through the whole body of the plant. The circulation within a plant is not carried on through the agency of tubular channels, but only by the passage of sap in all directions from one cell to another.

Since the cells have no openings, it is somewhat difficult to understand in what manner the fluid can enter into the plant from without, and by what means it can inwardly pass from cell to cell. This phenomenon, however, is dependent on the peculiar quality both of vegetable and animal membranes and fibres—viz., that they are permeable by many fluids, without being dissolved by them. Experiments show that this permeative action is carried on in accordance with definite laws. When two fluids of unequal densities—as, for example, an aqueous solution of sugar and mere water—are separated from each other by a diaphragm of pig’s bladder, we perceive a constant tendency on both sides to restore the equilibrium in the density of the two fluids. A portion of the water penetrates the bladder, mixing with the solution, and a portion of the latter finds its way to the former by the same medium. In this experiment one important fact is to be observed—viz., that the lighter fluid always passes through the separating medium more rapidly to the denser than vice versâ; consequently, in this experiment more of the water passes through the bladder to the saccharine solution than of the latter to the water. This permeative capability of the tissue of vegetables and animals is called endosmose.

The cells both circulate the sap and alter its condition, so we find differing substances in the same plant. The cell as described creates new cells, and the force with which the sap rises is rather greater than the pressure of the atmosphere.

The vascular, or fibrous tissues, are illustrated in the margin (fig. 741). They usually contain air. Some plants have no vascular tissue, and are termed cellular plants—such as mushrooms, fungi, mosses, and seaweeds. Many contain both tissues, and these are the more highly developed kinds.

Fig. 742.—Cells of epidermis (leaf).

Sometimes we find a milky juice in plants. This is called latex; and caoutchouc is always present in it. This juice is contained in tiny tubular vessels, which have their origin in the new cellular tissue of the lactiferous plants.

Fig. 743.—Stomata.

The tissue of the cuticle, or epidermis, which externally covers all parts of the plant while they remain green, is of a peculiar nature, and demands special consideration. It is formed of flat tubular cells, very much compressed, and in close contact, with the exception of some parts where the stomata, or mouths, are placed. In fig. 742 a section of the leaf is represented, the large transparent empty cells of the epidermis, and above these the parenchymatous cells of the leaf filled with greenish-coloured granules. In four places (fig. 743) stomata (s s s s) are seen, which have their openings surrounded by parenchymatous cells disposed in semilunar forms. Under each stoma (mouth) there is a hollow space which is connected with the intercellular passages of the leaf. These stomata, represented in fig. 743, are so numerous on the under side of the leaf, that hundreds have been counted in the space of a square line. Through these minute organs an intimate connection exists between the interior of the plant and the external air.

The epidermal cells not unfrequently exhibit very abnormal formations. When much extended in length they appear as hairs which are frequently branched, and in many plants they contain an irritating sap (in the nettle, for example). Bristles, prickles, glands, warts, and especially the substance which forms the well-known cork, are all due to the metamorphosis of this exterior integument.

Flowering Plants.

:

Fig. 744.—Water lily.

Fig. 745.—Transformation of petals into stamens in white water lily.

Flowering plants have certain distinct features which cannot be mistaken, for they grow well above ground, and can easily be examined. There are a hundred-thousand different species of flowering plants, and a visitor to Kew can study them there. Any child can tell a flower when he sees it, but a flowering plant is no more restricted in Botany to actual bright blossoming plants, than the term rock in Geology means a mass of stone only. Flowering plants may be either very gorgeous or very simple; and so long as they contain a reproductive apparatus they are flowering plants. The rose is a flowering plant, but the oak is equally one. The beech tree and the primrose are classed under the same heading.

Fig. 746.—Pistils of violet.

Fig. 747.—Tetradynamous stamens.

Flowering plants must possess stamens and pistils, which bring forth seeds which contain an embryo, and the germination of seeds can be easily perceived by any one who will take the trouble to soak them (say “scarlet runners”) in warm water, and keep them warm in moist flannel. The process may then be examined at leisure.

We need hardly insist, after what we have said, upon the necessity for some air and light, or remind the reader that he must not keep the seeds in a close, dark place, though light is not so necessary at first as air. The embryo connects the “cotyledons” or halves of the seed, and this develops into a tiny rootlet or “radicle,” and upwards into the stem, the commencement of which is known in botany as a “plumule.” The rootlet seeks nourishment from the ground. The albumen secreted in the cotyledons feeds the embryo, until (in some cases) it is exhausted and they die away. In other cases they grow up and obtain food for the young plant in the air. Some plants have (like wheat) only one seed-leaf, or cotyledon; and these kinds are called monocotyledons, or endogens, in which the growth is upright. The others are called dicotyledons, or exogens.

Fig. 748.—Polyadelphous stamens.

>Fig. 749.—Pistil of primrose.

So far now, perhaps, you may understand that the outer covering of the seed is called the testa; the opening which may be perceived in the ordinary bean near the dark spot is the micropyle, or little gate; that the halves of the covering are termed cotyledons, or cups, and that the embryo sprouts upwards and downwards, the upper part of the stem being the plumule, and the lower portion the radicle. Even if the seed be put micropyle upwards into the ground, or between layers of flannel, to germinate, you will find that the radicle will always curve downwards.

Fig. 750.—Diadelphous stamens.

Fig. 751.—Fibrous root.

The root then being displayed, it pushes its way into the ground to seek for nourishment, and when the proper moisture has been admitted to the seedling, which has been reposing in the cotyledons all the time, it sprouts up rapidly. The root and its fibrous extremities have been pushing and insinuating themselves into and through the ground, and by small knobs or suckers known as spongioles, the rootlets or fibrous parts of the root pick up sustenance for the plant, and it is then carried by tubes to the root, and so on throughout the plant, and with air ducts serve to keep the plant alive.

The stem emanates from the plumule, and in a short time little knots develop upon it, which are the incipient leaves. The knots are divided into nodes and internodes, because they appear on different sides of the stem and intermediate, so as to alternate with each other, and are really buds. The issues unite also into leaf-stalks or petioles, and extend into the leaf-frame or skeleton as we see it when the leaf has decayed. So thus we have an upward and a descending growth, which respectively constitute the stem and root of a flowering plant.

Fig. 752.—Tuberous (fasciculated) root.

Some trees have roots growing from the stem, as in the banyan tree, and roots can produce stems as well as the latter can form roots. The uses of roots are so well understood that we need not particularize them. In many trees we find what are termed lenticellæ, like holes in the bark. These fissures will put forth roots under favourable circumstances. These stem roots are called adventitious, and by taking “cuttings” from plants we make good use of them for propagation.

Fig. 753.—Banyan tree.

But there are underground stems as well as those which flourish and climb above it. “Bulbs” and “tubers” are common instances of these underground stems, or “rhizoma,” which are horizontal. The ordinary stems are termed “aerial” stems to distinguish them from the earthy and subterranean. The aerial roots of ivy are only used for support, and are not its proper roots, though some parasitic plants strike into the trees and are nourished by them.

The Stem.

Fig. 754.—Transverse section of exogenous wood, showing the growth of nine years.

The stem is that portion of the plant-axis which grows upwards or above ground, and may be, as we have just read, subterranean. As the great function of the root is to procure sustenance for the plant, the stem assists in carrying the nourishment through the branches and leaves. We shall find two forms of stem—the underground, or root-stock, and the stem proper. There are in these two former several varieties as under:—

1. The Bulb, which is a short globular stem surrounded by thick leaves, and producing buds—as, for example, the onion.

Fig. 755.—Section (magnified portion) of the small cut a.

2. The Tuber, similar to the foregoing in shape, having no leaves, however; the potato is an instance.

3. The Rhizome (root-stock), like a root only producing buds, which roots do not. The iris will serve as an example.

The varieties of the stem-proper are:—

(1) Filiform, or thread-like, simple, or branched, as in mosses.

Fig. 756.—Section of an endogenous stem.

(2) The culno, a thin, hollow, and frequently-jointed stem.

(3) The palm or simple stem, seen in tree-ferns and palms. It is marked by the scars of dropped leaves.

(4) The stalk, very common, of a green hue, and its life is limited to a twelve-month as a rule. The so-called “stem” of the hyacinth is not a stem, it is a stalk, or flower-stalk, pushed forth for a temporary purpose.

(5) The ligneous stem is the perfected kind, and an example will be apparent in every tree.

The duration of the stem of a plant is usually the same as of the plant—so we have annuals, biennials, and perennials. The substance of the stem determines its character, so we may have it solid, or soft, hollow, tubular, flexible, rigid, or a tough stem. There are fibrous, herbaceous, and juicy stems. They may be directed uprightly, straight, procumbently, arched, or creeping, above, or underground, climbing, clinging, floating, or twining.

There are many plants with little or no stem deserving the name, as in the onion; and we must all remember when studying botany that it is not the place where a portion of a plant may be found that constitutes it a root or a stem. The form and structure should be studied, and its purpose in creation. So stems may be underground and roots above it. The root and stem, briefly treated of in the foregoing paragraphs, have certain points of resemblance, inasmuch as both consist of a main or trunk line, so to speak, from which branches diverge as “rootlets” and “twigs”; and how beautiful the latter are any one can see in a good photograph of a wintry landscape. But stems have nodes and internodes, and roots have not, and this is the great and apparent difference.

The covering of plant-stems is varied, and many instances of such clothing will occur. We have woolly stems and hairy stems, which develop into thorny ones—for thorns are only strong hairs. Spines and stings and prickles defend the stems, and keep rude hands from meddling. We will now cut the stem and see what it is composed of, and how it looks inside. We have only to cut it across and again perpendicularly to find out a great deal about the interior structure of the stems of branching plants (exogens).

The elder, from which the whistle of our boyish days is fashioned with a penknife, will serve any lad for an illustration. Inside we find what is called “pith,” which is cellular tissue. Round this is fibre, and outside is a skin, or the plant-cuticle. We may remark that the tissues of flowering plants are characteristic of the monocotyledonous and the dicotyledonous plants. Of the former we append an illustration,—a section of palm-stem,—and we find bundles of vascular tissue dispersed apparently at random amongst the cellular tissue of the parenchyma, or cellular tissue. These stems do not grow by the increase of the existing vascular tissue, but by their new production at the circumference, and so they grow in both directions, laterally and uprightly. These plants belong to the Endogens, and if Indian corn be grown we shall have full opportunity to study the formation. In cutting a fern stem we are familiar with the “oak” pattern of the matter it contains. We have few specimens of endogens in England.

The dicotyledonous stems are common to our trees and most plants, and may therefore be considered with advantage. The stem consists of the vascular tissue called “pith,” and we give an illustration of the cells magnified very considerably. The arrow indicates the outward direction (fig. 757).

Fig. 757.—Dicotyledonous stem.

We here perceive the vascular bundle proper surrounded by a very large-celled tissue, aa′bef. The almost square cells, aa′, form the epidermis on which follows the less dense cellular tissue of the bark. The latter surrounds a half-moon-shaped bundle of bast-cells, c, which are separated in the direction towards the interior, by a layer of cambium, dd′d″, from the bundles of vascular tissue, consisting of vessels and longitudinal cells. The latter tissues may be distinguished in the transverse section by the thicker walls, gg, and by their greater breadth, hh. It is further to be remarked that the cambium transparent tissue, dd″, appears on both sides of the bundles of vascular tissue, and extends to the next bundle, and thus presents an uninterrupted circle throughout the entire circumference of the stem.

Fig. 758.—Stem one year old.

On examining the section of a one-year-old dicotyledonous stem, magnified six times, as in fig. 758, we perceive several parts clearly distinguishable from each other, corresponding with the arrangement of the bundles of vascular tissue.

Enclosed by the epidermis, a, is a large-celled tissue, b f and m, in which a number of vascular bundles form a circle. In each of these we notice that the outer portion, consisting of bast-shell, c, is separated by the cambium, d, from the inner woody portion, e. The cambium forms a closed circle which penetrates through all the vascular bundles.

In the course of the further development of the stem, the parts, a b c, constitute the bark, the vascular bundles, e, the wood, and the cellular tissue, f, its pith. The tissues, m, penetrating between the vascular bundles, are called the medullary rays. The cambium is to be regarded as the most important part, since it is the source of new bundles of vascular tissue which year by year increase the circumference of the stem.

Fig. 759.—Stems three and five years old.

The growth of a dicotyledonous stem is continued by the formation of a new circle of vascular bundles on the circumference of the stem in the second year. Each new bundle, as has already been shown, is produced in the cambium, and consequently is deposited between the wood and inner bark.

Thus every year a new layer is deposited between the previous formation and the bark; and a section will exhibit these concentric rings of wood obviously distinct from each other; and as one year is requisite for the formation of a single layer of wood, these depositions are named annual layers or rings. In fig. 759 we have a representation of a stem three years old, and one of five years of age.

The number of rings in the stem do not invariably agree with the number of years the tree has been growing, but it may be accepted as a rule.

The stem is the medium of communication between the roots and leaves at first; but after a year this important duty is deputed to the cambium layers of new woody tissue, etc., and as time goes on the living power has accumulated immediately under the bark. So although the tree be quite hollow it will live. The interior has been closed up by deposition of wood and has decayed; but the life functions being relegated to the bark, the old tree lives on. If we remove the rind all round a tree it will die.

The Leaves.

Fig. 760.—Compound leaf.

When in the spring the young leaves appear upon the trees, and as summer advances they become fully developed, we are all grateful for the beautifully varied tints of green, and for the shade we can so fully enjoy. The study of leaves is a most interesting and instructive one, and nobody should omit to examine them. Their forms are infinite, or, at any rate, countless; their size as varied as their forms. Many attributes of the leaf will occur to every reader, and we will briefly describe these essential organs of plants. Air and light are necessary to the development of leaves, and their principal use is to present a surface to the food material which the plant absorbs. They breathe, as it were, and absorb the carbonic acid from the atmosphere. These functions are called “assimilation,” “transpiration,” and “respiration,” which we will detail by-and-by.

Fig. 761.—Simple leaf.

Leaves are distinguished according to position and duration. Some leaves have very simple forms, others are compound, so to speak. Some are plain and rounded, others are toothed, like the holly. The skeleton of a leaf is a very interesting study, and it will show the beautiful structure of these common objects. The delicate lines of the green leaf are “veins,” or sap-vessels, which convey the necessary nourishment. The leaves are called the “embryonic” (seed-like), the radicle, or root-leaf, the stalk-leaf, and the stipules, which grow at the base of stem-leaves, and the floral leaves, which bear the flowers or fruit buds. Leaves which are developed at the end of a chief axis are termed blossoms. Of course it must be understood that all the different kinds of leaves do not occur upon the same plant. The leaf may be accepted to mean the stem-leaf.

Fig. 762.—Net-veined leaf.

Leaves are folded up in various ways, and the manner in which this is accomplished is termed the vernation of the plant. The leaves of endogens and exogens differ in their veining. The former veins do not touch; there is none of that beautiful interlacing which we find in the exogenous leaves. In the former the veins rise from base to apex, curving as they advance, as in the well-known lily of the valley. This “nervous system” of the leaf is its “venation,” and the veins distributed in the blade or lamina of the leaf are twofold,—as remarked,—ascending in curves, or diverging from a central nerve called the “mid-rib.” These lateral nerves are either parallel or “reticulate”—that is, net-like.

Fig. 763.—Linden tree.

We will now examine the forms of leaves which are regulated by the divergence and extension of the divisions of the mid-rib. Thus we get an orbicular, or peltate leaf; palmate, digitate, and pedate forms also occur, as may be seen in the illustrations, pages 672 and 673, where all the varied shapes can be studied. The leaf consists of a petiole or stalk, and the lamina or blade. The petiole is composed of bundles of vascular tissue; the lamina is formed by their extension, the interstices being filled with cellular tissue. So we perceive that the leaves and stems are composed of similar materials. To defend the tissue a skin, or epidermis, is placed upon the surface of the leaf, and this epidermis is full of breathing holes, or pores, called stomates (compare page 664). There are also cells filled with chlorophyl, which gives the leaf its green tint.

Fig. 764.—Stomates, highly magnified.

The petiole may be absent in a leaf, and when it is the leaves are termed sessile, or sitting leaves. These leaves sometimes coil round the stem, and are called “amplexicaul,” or stalk embracers. These are simple leaves. Compound leaves are composed of several blades or laminæ on a stalk, and are seldom sessile. Simple Leaves are almost innumerable in form and variety. Leaves may be equal or unequal, acicular or linear, rounded or oval, cordate or obcordate, reniform or sagittate, perfoliate or connate, crisp, whorled or truncate, retuse, acuminate or mucronate. The margins of simple leaves again are entire, deft, notched, crenated, crenulated, sinuous, or dentated. They are pinnatifid, multifid, or lobed, according to the divisions of the leaf.

[LEAVES.]

Compound leaves are also divided into classes. The pinnate, as the rose-leaf, the clover trefoil. There are “doubly pinnate,” the digitate, as in the horse chestnut. Compound and simple leaves can be readily distinguished by inspection, for the former are “articulated” to the stalk and can be separated, but the simple leaves will be torn, for they are confluent throughout.

Leaves are evergreen or deciduous, accordingly as they retain or shed themselves. The ordinary leaf is deciduous; the fir and the yew and the imported laurel are evergreens. We have very few of these as natives of England, the ivy, yew, and fir being the three most common. Sometimes a plant peculiar to Killarney, and known as the arbutus, is included in the list. But the Scotch fir and the yew are distinctly native evergreens.

The detailed characteristics of leaves must be passed over until we come to the fly-catching leaves—such as Venus’ fly-trap, the droseras, and nepenthes, which appear to catch and devour insects for food. The Venus’ fly-trap may be examined, and we shall find the leaves covered with tiny and very sensitive hairs. Often a fly happens to alight upon the leaf, which is extended in a most innocent manner (see illustration). As soon as the fly settles the leaves close, and the digits lock tightly together, thus preventing the escape of the prey. The droseras, sarracenias, and nepenthes also kill their food. The sarracenias form curious cups, into which insects are enticed in search of fluid, and then, as in the case of the house-haunting cockroach, they cannot get out again. The nepenthes have a cup and lid for insect-catching, and within the cup a liquid is secreted.

We will close this portion of our subject with a quotation from a recent article upon botany referring to leaf arrangement. The writer says:—

Fig. 765.—Leaf of Dionæ.

Fig 767.—Leaf of Nepenthes.

Fig. 766.—Sarracenia.

“Efforts have been made to determine the laws to which these various modes of leaf-arrangement may be referable. The result is found in the doctrine of ‘Phyllotaxy,’ as it is called, the fundamental principle of the whole being that Nature, in the disposition of the leaves upon the stem, works upon precisely the same idea as that which is set forth so distinctly and elegantly in the common pine-cone; and, on a minor scale, in the beautiful cone of the female hop; not to mention the quasi-cones of many species of tropical palm, such as the Sagus and the Mauritia; nor to mention either, the very delicate repetition of the whole series in the florets of the Rudbeckia and the ripening fruits of Chaucer’s daisy. In every one of the flower and fruit arrangements mentioned, the idea is the spiral,—the same sweet old fashion which we have had in the twining stems of the convolvulus, the woodbine, and the scarlet bean; which comes out again in many a sea-shell, and in human ringlets; and this idea, according to ‘Phyllotaxy,’ governs the position of the leaves. Following alternate leaves up the stem, their sequence is clearly spiral. Through the non-development of internodes, they are brought closer and closer together; and even when the entire mass of foliage is concentrated and condensed into the rosulate form, as in the houseleek and the Echeverias, the spiral prototype is still distinguishable. The whole matter has been reduced to one of arithmetical exactitude; and for those who love calculations and “fractions,” the determination of the spirals, their continuity and intermixture, supplies abundance of curious entertainment. All three modes of leaf-arrangement are found in certain herbaceous plants, none disclosing this particular kind of playfulness more plainly than the common pyramidal Loosestrife, Lysimachia vulgaris, and the purple Lythrum of the waterside, in each of which very handsome wild flowers, alternate, opposite, and whorled leaves may be found in near neighbourhood. Alternate and opposite leaves are also met with, side by side, in various species of Myrtaceæ; and imperfectly, upon young shoots of the common ash-tree. The rule is, nevertheless, that there shall be uniformity, and in many of the largest natural orders the rule is never broken. In the Rosaceæ the stem leaves are invariably alternate; in the Gentianaceæ they are invariably opposite.”

Fig. 768.—Branch of horse chestnut.

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CHAPTER LII.
FLOWERING PLANTS.

ORGANS OF INCREASE AND REPRODUCTION—THE FLOWER—THE CALYX—THE COROLLA—THE STAMEN—THE PISTIL.

Some of the simplest plants are propagated by spores, which are detached, and fall upon the ground to vegetate; but in the case of the higher orders the reproduction of species is a much more elaborate process, and is carried on by means of certain organs called flowers. Small buds, or ovules, are formed, which develop into seed. Plants also produce buds, which grow upon various parts of it, and are capable of reproducing their species. We will first speak of Flowers.

Flowers are not only the lovely blossoms we cut and place in our rooms, but the reproductive organs of plants which may be very plain and simple or gorgeous and fragrant, and in all probability the so-called flowers are few in comparison to the unrecognized flowers. Trees and bushes flower equally with the rose and the pink and carnation. Vegetables flower as well as the lily, though we do not recognize it so well. Let us now examine the “flower.”

Flowers may consist of four parts, but it is not absolutely necessary that they should contain more than two. The four portions of a complete flower are—

1. The Calyx.
2. The Corolla.
3. The Stamen.
4. The Pistil.

The two last mentioned are essential. The four organs are placed around a pedicel or peduncle (flower stalk), and are known as floral whorls.

The Calyx is the outermost whorl of all when all exist. The portions of the calyx are known as sepals.

The Corolla is usually the showy portion—the attraction of the flower. The pieces of the corolla are called petals. The sweet fluids of the plant are here concealed.

These parts—the calyx and corolla—are known as the floral envelopes, or “perianth.” The tulip has one whorl only, and it is called the envelope.

The calyx sometimes falls before the flower is full blown, as in the poppy. Its lower portion is the “throat,” and the shape of the organ varies, as will be seen by the illustrations.

Fig. 769.—

1. Tubular.	2. Clavate, or club-shaped.	3. Tubinate, or top-shaped.
4. Campanulate, or bell-shaped.	5. Funnel-shaped.	6. Urceolate, or urn-shaped.
	7. Globular.

The sepals are usually three to five in number. The poppy has two, and the well-known wall-flower four free—that is, disunited—sepals. The primrose possesses five. The calyx is the outside rim of all, and we may thus remember it, because its sepals alternate with the petals of the corolla. The petals may be formed cup-fashion, as in the lily of the valley, and here we have these sepals and petals in groups of three each.

Fig. 770.—Trimerous corolla.

Fig. 771.—Tetramerous.

Fig. 772.—Pentamerous corolla.

Fig. 773.—Monopetalous corolla.

The petals differ from ordinary leaves, and in them we find all the beautiful tints and the odour we imbibe from blossoms. The forms of corolla correspond to those of the calyx, and are called by the same names. But when corollas are absent the petals of course cannot provide the necessary colours for the flower. Then the calyx is gifted, and the sepals are brilliant. Thus Nature provides for everything.

Corollas are found with five or ten petals, and sometimes with three, six, and nine—the numbers always doubling or adding the original number. There may be four petals or eight, as in the “tetramerous” corolla (fig. 771). Instances of others are illustrated, and a plant whose petals, sepals, and stamens are numerically equal, or are multiples of each other, are termed “symmetrical.” The “regular” flower does not vary much, as the petals are of the same size and shape, but there are many “irregular” flowers—as the pea—in which portions of the calyx or corolla are of different shapes. The “labiate” and the “campanulate” are illustrated in figs. 774, 775, including the convolvulus and the snap-dragon. These are but a few examples of an almost endless diversity. The “regular” flowers—exemplified in the buttercup and convolvulus—always present the same figure to the observer.

Fig. 774.—Labiate corolla.

Fig. 775.—Campanulate.

To the petals the beautifully-varied colours of plants are due, and though it is not possible to enter upon the subject here, we may conclude that the various beauties of the colours of flowers are owing to light and air acting upon the various “colouring matters” contained in the plant. Seeds planted in a dark cellar will spring up pale; admit light, and they will become green, for light thus acts upon the chlorophyl. But the flowers of the plant are not so dependent upon light, as can easily be proved. Many interesting experiments have been made upon flowers by acids and gases.[36]

The Stamens are the next in order for our consideration. They are found within the petals (or the calyx if no petals be present). Stamens vary very much in different plants both in number and general features—but, as in the case of petals, they keep, as a rule, to certain numbers and doubles of them. The stamen consists of two portions—a lower, thread-like part called the filament, and an oblong bag or head, termed the anther. This contains a powdery matter called pollen, and is the essential part of the stamen. The filament, which corresponds to the petiole of the leaf, may be absent, in which case the anther is called sessile. A lily will show the stamens perfectly, the anther being prominent in many other plants also, such as daffodils and fuchsias.

The stamens are very important organs with regard to the classification of plants—for number, length, and position, whether free or united, are all characteristic features. The length of filaments is always the same in the same kind of plant, and therefore is a very palpable test.

The anther contains the pollen, a powdery matter, usually yellow-coloured, but sometimes also red, brown, violet, or green-coloured. Pollen-grains vary from 1/20 to 1/300 of a line in diameter. Under a powerful microscope they appear as ellipsoidal, or sometimes spherical, triangular, polyhedral vesicles, filled with a granular semi-fluid matter. To effect fecundation, the pollen-grains must come into contact with a certain part of the plant which is intended to receive them, and which is called the ovule, and is found in the fourth or innermost verticil of the flower, the pistil. Of the further development of the ovule, we shall have occasion to speak in the paragraph treating of the seed.

At the proper time the anther opens and discharges its contents, the pollen-grains, some of which reach the place of their destination. The position of the stamens to the pistil is usually such that the latter can readily receive the pollen-grains. In many plants, however, the stamens are too short to reach the pistils; or the two essential organs of reproduction are in separate flowers, or even on different plants. In such cases, the conveyance of the pollen from the anthers to the pistils is effected by the agency of the wind, or by that of insects, and more particularly by the bee. If the anthers are removed from the flower previously to their opening, no fruit is produced.

Varieties of flowers and fruits are produced artificially, by shaking the pollen of one plant upon the flowers of another, deprived of the stamens. Many esteemed sorts of stock-gilliflowers and pinks have been produced in this way.

The pistil constitutes the fourth and innermost whorl, and occupies accordingly the centre of the flower and the apex of the axis, whose growth is terminated with the production of the fruit.

Fig. 776.—Pistil.

The pistil also is formed by one or several modified leaves, called carpels, in this part of the flower, and which exhibit a more marked resemblance in colour and structure to the ordinary leaves than the stamens and petals do. The formation of the pistil from the leaf may be considered to proceed in this manner: that the edges of the leaf are folded inwards and unite, whilst the mid-rib is prolonged upwards (fig. 776A). The place where the margins of the folded leaves are united is called suture or seam (ventral suture, in contradistinction to the mid-rib, which is called the dorsal suture); and it is here that the seed-buds or ovules are developed.

The pistil consists of two parts—viz., the ovary or germen, which contains the ovules or young seeds, a, and the stigma, b, either placed upon the ovary, or upon the style, or stalk, which is between the stigma and the ovary.

A pistil may be of one carpel (simple), or of more than one (compound). The carpels or the carpellary leaves are the “ovaries.”

The pistil is a very important test for the classification of plants; some trees have no pistils, and the ovules are consequently naked. Such plants are called gymnospermæ. The coniferæ (firs and pines) are thus recognizable, and the position of the ovule is very much that of the ordinary bud.

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CHAPTER LIII.
FLOWERING PLANTS (continued).

THE FLORAL AXIS—INFLORESCENCE—FRUIT—SEED—NUTRITION OF PLANTS—ABSORPTION OF CONSTITUENTS.

There are certain arrangements and mutual relations of the various portions of the flowers which we have mentioned that it is useful to consider. The floral axis refers to the position of the verticils, and inflorescence signifies the arrangement of the flowers on the stem. Flowers which possess both stamens and pistil are hermaphrodite; those with only stamens are male; those with the pistil female flowers. If both organs be absent the flower is neutral.

Plants bearing flowers in clusters form several distinct groups, to which appropriate terms are applied indicative of their respective form of flora arrangement.

Fig. 777.—(1) Spike. (2) Catkin. (3) Spadix. (4) Cone.

In the examination of this kind of inflorescence (indefinite or axillary inflorescence), the first object of remark is the general or primary peduncle, termed rachis, and which bears numerous leaflets called bracteoles or bractlets, from whose axils arise the pedicellate or sessile flowers. The lower bracts often produce no flower-buds in their axils, and form instead a whorl surrounding the heads of flowers on the primary axis, and which is called involucre (as in the sun-flower, for instance).

Fig. 778.—Raceme.

Fig. 779.—Panicle.

Fig. 780.—Corymb.

The different varieties of axillary inflorescence are determined principally by the elongation or depression of the axis, the presence or absence of stalks to the flowers, and the form and nature of the bracts. We distinguish—

Fig. 781.—Umbel.

Fig. 782.—Capitulum or ball.

1. (1) The spike (fig. 777). In this form of inflorescence, sessile or short-stalked flowers are arranged along the rachis in the axils of the bracts; the spike is said to be compound when small spikes or spikelets arise again from the bracts of the secondary axis. (2) The catkin or amentum (fig. 777 [2]); a spike, usually pendulous, which falls off, rachis and all, by an articulation, as in the willow or hazel. 3. The spadix, a thick fleshy spike (fig. 777 [3]); examples, arum and calamus. 4. The cone, a fruit-bearing spike, covered with scales (fig. 777 [4]); examples, the coniferæ. 5. The raceme or cluster, a spike with the flowers on longer pedicels (fig. 778); examples, the currant. 6. The panicle, a branching raceme (fig. 779, Yucca gloriosa). 7. The thyrsus, a dense panicle, with longer peduncles in the middle than at the extremities; example, lilac. 8. The corymb, a raceme, in which the lower flower stalks are elongated and raised to nearly a level with the upper (fig. 780)—example, cerasus mahaleb. 9. The compound or branching corymb, a corymb in which the secondary axis again sub-divides; example, Pyrus terminalis. 10. The umbel: in this form the primary axis is greatly depressed, and the peduncles arise from a common point, and spread out like radii of nearly equal length, a whorl of bracts (involucre) surrounding the common base. In the compound umbel (fig. 781), Daucus carota, the secondary axis ends in small umbels surrounded by bracts, which is termed an involucel. This is observable in the umbelliferous plants—carrot, parsley, hemlock, etc.

Fig. 783.—Inflorescence.

A very peculiar kind of inflorescence, which characterises the great family of the compositæ, is illustrated by fig. 783. We see here the enlarged floral axis or receptacle, a, surrounded by several whorls or bracts, b b, which constitute a general involucre; the membranous bracts, (paleæ), b´ b´, seen in the receptacle, bear in their axils the sessile florets, c and d, which either have a calyx, e e, or not. The florets on the receptacle are either all of them tubular (d) or ligulate (tongue or strap-shaped); florets (c) are associated with the tubular ones. The receptacle is not always flat, but frequently presents a convex, globular, conical, concave, etc., shape.

In the absence of paleæ the receptacle is said to be naked. The florets at the margin, or circumference, are termed marginal flowers, or flowers of the ray; the florets in the disc (centre), central flowers, or flowers of the disc.

Some plants bear male and female flowers on the same stem. These are termed monæcious plants. The oak is an instance. The diæcious plants are those which bear stamens and pistil, or separately, on different plants, like willows. We will now glance at the functions of the stamens and pistil. The ovule has been mentioned as a tiny body in the ovary, and it consists of a nucleus, and cellular tissue surround it, leaving a small hole called the micropyle, into which the pollen tube enters after passing through the ovary. As in the animal creation, the unions of different families succeed best; no close relationship will fertilize so well as with other flowers.

Fig. 784.—Male flower of nettle.

Fertilization is accomplished in two ways; (1) by the action of the wind, by which the pollen is carried away to other plants; and (2) by means of insects—the bee particularly. These flowers have distinctive qualities relatively. In the case of the pine the pollen is powdery; so those plants which are thus fertilized are the diæcious species, which include the poplar, the oak, and the birch, as well as the pines. These are all wind-carried pollen plants. The nettle is illustrated here with male and female flowers.

Fig. 785.—Female flower of nettle.

Plants fertilized by insects are visited by them, and they carry away upon their heads, or bodies, the pollen, which is then thrust into the stigma by the insect; or perhaps birds may carry the pollen in the same way after sipping the nectar, and thus playing an unconscious, but most important, part in the economy of nature.

Fig. 786.—Erect ovule.

We always find the ovule at the termination of an axis; it is unable to form a seed alone. The pollen grains must fertilize it, and in consequence many ovules come to nought. The ovule is produced in the pistil, which, as before stated consists essentially of two parts—the ovary and the stigma; the latter secretes a fluid to hold the pollen. We annex the representation of a highly-magnified pistil (vertical section, fig. 786a). The pollen grains are indicated by d, attached to stigma, c, projecting through the style, b, into the ovary, a, and passing through the ovules.

With the transmission of the pollen to the ovary of the pistil, the functions of the anther and stigma terminate; accordingly these parts of the flower rapidly wither and decay after fertilization. The filaments, the style, and the petals speedily participate in the decay, but the sepals remain sometimes persistent in an altered form. The ovary and its contents alone proceed in their further development, and undergo material changes, in which, however, the bracts and the calyx often participate.

Fig. 787.—Dorstenia.

Fig. 788.—Dandelion.

Fig. 789.—Apple.

The fully developed and matured ovule, the seed, is, of course, regarded as the essential part of the fruit; the enlarged ovary forms the pericarp, enclosing the seed. The form of the pericarp determines the external appearance of the denomination of the fruit. The structure of the fruit, and the arrangement of its parts depends in a great measure upon the number and position of the carpellary leaves in the pistil, and the manner and extent of their union, and the extent to which their edges are folded inwards.

Fig. 790.—Follicles of larkspur.

Fig. 791.—Sycamore fig.

The carpellary leaves occupy the summit of the floral axis. The axis terminates either in one single carpel, in which case the ovary is one-celled, or unilocular; or the axis is surrounded by several carpels, in which case the manner of their union determines the number of cells in the ovary.

The Fruit.

Fig. 792.—Sycamore fig.

Fig. 793.—Fruit of a composite.

Fig. 794.—Section of a berry.

The carpels are the chief agents in the formation of the fruit, and they form the endocarp (core), and sometimes the whole pericarp, or seed-vessel. Upon the nature of the various parts and the changes they undergo during the ripening of the seeds the nature of the fruit depends. The fruits are classified, some being the produce of a single carpel, others of several united carpels.

Fig. 795.—Umbelliferous plant and its fruit.

Fig. 796.—Three-celled capsule.

Fruit, in botany, is by no means limited to the juicy products of trees or plants which are so refreshing in the summer weather, and so acceptable in any form. In plant life the herb yielding seed produces a fruit equally with the orange or the apple. The fruit is the outcome of the varied processes of the plant. We may trace the plant from its tiny, sometimes very minute seed, through stem to flower and seed again. “In the final struggle, even when life is hopeless, and starvation, in consequence of drought, is imminent—when all is hopeless and barren, the plant will make an effort to produce its fruit and flower.” This is a very touching and interesting fact in nature—this last attempt to beautify the earth and to propagate its species for the use of man.

Fig. 797.—Poppy.

Fruit, then, is not limited to the market and the stall.

This statement scarcely needs proof; but if we consider for a moment the number of “wild” fruits—the parents, probably, of our table-fruits—we find many we cannot eat. In short, out of the hundred thousand plants which bear flowers scarce one two-hundredth part serve us as producers of edible fruits.

Fig. 798.—Three-celled capsule.

Fig. 799.—Water melon.

The fruit is the result of the flower, and if any objection be made by readers on the part of the common fig, it will be found that this appreciated fruit really consists of male and female flowers that are fertilized by the action of minute insects, which enter and depart (sometimes they die, and are found dead and black in the figs). No blossom is perceived on the tree, because within the green sac the so-called “seeds” (really the fruits) are developing. A fig is a sac full of fruits.

Fig. 800.—Legume.

Fig. 801.—Legume opened.

The legume or pod is formed of a single carpel bearing seeds. We annex illustrations of the pod. The covering is called the pericarp, and the parts when opened separate into valves. Dehiscent fruits shed their seeds, indehiscent fruits do not; they lie within the seed-vessel, like the acorns and nuts. These are dry fruits, but there are others of a soft nature, such as apples or gooseberries.

Fruits are variously named, and underneath will be found a list. We have the aggregate, like the mulberry, etc.; the dehiscent fruit of one carpel like the pea, etc.; the simple fruits as cherry, nettle, wheat, etc. The dandelion fruit is often a precious object in children’s estimation, as it is blown away to ascertain the time. There are indehiscent fruits with many carpels,—the common buttercup, for instance, and the strawberry. A list is added.

Fig. 802.—Legume (pea).

Fig. 803.—Gland (acorn).

Fig. 804.—Stobule (hop).

Fig. 805.—Drupe (plum).

Fig. 806.—Berry (currant).

a. Fruits which are the Produce of a Solitary Carpel.

1. The gymnospermous fruit, where the seed lies naked in the axils of the ligneous bracts, as in the cone of the fir and spruce tribe.

2. The legume or pod, which is formed of a solitary carpel bearing seeds on the ventral suture. It characterises the pea and bean tribe (leguminosæ).

3. The follicle is a mature carpel containing several seeds, and opening by the ventral suture. There are usually several follicles aggregated together; examples, larkspur, monkshood, evergreen.

b. Fruits which are the Produce of Several Carpels United.

4. The capsule consists of two or more carpels, either simply laterally united (one-celled or unilocular capsule), or folded inwards towards the axis, but without reaching it (spuriously multilocular capsule), or uniting with the axis (bilocular, trilocular, multilocular capsule). Examples of capsular fruit—mignonette, balsam, violet, poppy, etc.

Fig. 807.—Capsule (poppy).

Fig. 808.—Siliqua (shepherd’s purse, wallflower).

5. The siliqua or long pod is formed of two carpels, and longitudinally divided into two parts by a spurious dissepiment called the replum; examples—cabbages, stock, wallflower, etc. The silicula is a broad and short pod; examples—Iberis, shepherd’s-purse, etc.

6. The cariopse (caryopsis, having the appearance of a nut), is a monospermous or one-seeded fruit, with an indehiscent membranous pericarp, closely investing the seed or incorporated with it; examples—rye, wheat, and other grains.

Fig. 809.—Caryopsis (wheat).

7. The achænium is a dry, monospermous, indehiscent fruit with one seed; examples—cashew, ranunculus, strawberry, etc.

8. The nut or glans is a one-celled, indehiscent fruit, with a hardened coriaceous or ligneous pericarp; examples—hazel-nut, acorn, etc. The nucula, or little nut, is a cariopse, with a solid coriaceous pericarp; examples—buckwheat hemp, etc.

9. The berry (bacca) is a pulpy, succulent fruit, with soft rind; examples—the gooseberry and the currant. The pepo or peponida (pumpkin), illustrated by the fruit of the gourd and melon, and the hesperidium, illustrated by the fruit of the orange and lemon, are modifications of the berry.

10. The drupe (drupæ, unripe olives); the mesocarp is generally pulpy and succulent, the endocarp hard; examples—the cherry, the peach, the plum, etc.

11. The pome (pomum, or apple); the outer parts of the pericarp form a thick cellular, eatable mass; the endocarp (core) is scaly or horny, and encloses the seeds within separate cells; examples—the apple, pear, etc.

Fig. 810.—Nut (hazel-nut).

Fig. 811.—Strawberry.

Fruits consisting of the floral envelopes and the ovaries of several flowers united into one, are termed multiple or anthocarpous; the sorosis (cluster-fruit: example—the pine-apple, the breadfruit, the mulberry), the sycosis (fig-fruit), and the strobilus (fir-cone), form varieties of the anthocarpous or multiple fruit.

Non-Flowering Plants.

The cryptogamia or acrogens is the botanical term for these plants, of which we must be very brief in our description,—not that the subject is not worthy of a much larger space than we can devote to it, but our pages are not elastic.

Fig. 812.—Liverwort.

Fig. 813.—Hypnum.

There are numbers of plants without pistils or stamens properly so called. They are hidden from human observation—buried out of sight; and in the fern, moss, and other primitive plants they are thus hidden. There are several families of the cryptogamia, but two main sections include them all—viz., the cormogens and thallogens. These are sometimes known as cormophytes and thallophytes, but the former will be our terms, and they include the ferns, algæ, lichens, and mosses, with many other families, which we do not propose to examine in this summary sketch. The microscope will here be a great aid if not always absolutely necessary for any close investigation.

We are all familiar with the appearance of ferns, and we may commence with a few observations concerning them. They are an extensive family and very beautiful, some of the tropical species being particularly noticeable for elegance. We are here mostly concerned with the development of the plant. The polypod ferns fructify under the leaves or “fronds,” which open from a ball. The seed-cases or sorri are situated at the back of the fronds in brown spots, and when examined they will be found to be collections of capsules like tiny cases. There is a kind of band at the upper part which at the proper time is extended, and tearing open the capsule releases the seeds. These seeds or “spores” are very minute, and not properly seeds but buds, every one of which can generate seeds. So if we try to grasp in imagination the generating powers of a few fern fronds, we shall miserably fail in the attempt.

Fig. 814.—Horsetail.

Fig. 815.—Bryum.

Some ferns have the “spores” upon the summit of the frond. The osmundas belong to this family, and are known to all as the “flowering fern,” a contradiction palpable enough under the circumstances. The beautiful dust upon some ferns has been mistaken for “spores” by many people, but it is merely a natural ornament of the plant. The venation and vernation of ferns are very curious, but in the determination of ferns the only sure way is to consider the sorri and the venation. The differences that puzzle may be little or great, but when the sorri have been examined all doubts will be set aside.

There are about three thousand varieties of ferns known, and we give a few illustrations of them, although any detailed description is out of the question, for we have to mention the beautiful mosses of which there are in Britain more than five hundred different species, all extremely beautiful, perfectly innocuous, and even beneficial.

The Mosses and Algæ.

Fig. 816.—Diatoma vulgaris.

Fig. 817.—Club-moss.

These plants are extremely lowly in the score of creation, and also in stature. Very few mosses attain any elevation, only the “sporangia” shoot up, and the plants are very delicately formed, the leaves being all of the same pattern. They are common in damp situations, and thrive in woods, streams, and banks. The Fontinalis is a river moss, while the Hypnum is found in hedges. The Lycopodiaceæ or the club-moss family is intermediate between ferns and mosses. They are found in warm, moist climates, and contain a sort of brimstone. They grow well with ferns under glass.

The Musci or moss-family proper are useful in various ways. We have also the liverworts, which bear some resemblance to lichens. They grow between stones near water, or in damp situations. There are two distinct families, both beautiful when examined, and are named Marchantiaceæ, and Jungeramanniaceæ, or scale moss.

Fig. 818.—Scale-moss.

Fig. 819.—Various diatomaceæ.

The Thallogens or Thallogenæ include algæ, lichens, and fungi, which are the lowest of the plants, and all very much alike. The algæ are termed “protophytes,” and consist of living cells propagating by subdivision, or union. The thallogens have therefore no distinct axes, leaves, or stomata.

The algæ are thus simply cellular plants found in salt or fresh water, hot and cold. They sometimes appear as “slime.” Some contain silicia, and are termed Diatomaceæ, and these propagate by subdivision, and when they die their shelly covering remains, and we find the shells or cases in all earthy formations. These diatomaceæ have been raised from the beds of oceans, and Atlantic soundings have revealed their presence,—as mud, when examined, proves to be these remains of vegetable shells. Thus the infinitely little in the animal and vegetable worlds meet at the bottom of the sea, as well as on dry land.

There are marine and fresh-water algæ—the former familiar to us as seaweeds which possess air-bladders that children love to explode, and which assist the algæ to float. They attach themselves to rocks, generally at the base; the lovely colours of seaweeds are well known. They will be recognized under the name of “tangle” (fucus), which, when burned, gives kelp and barilla, which is full of iodide and sodium. The Sargasso Sea is composed of miles of algæ which live in the open ocean. The Carrageen or Irish moss is very nutritious and useful in consumptive cases. Indeed, all algæ, if not absolutely useful, are certainly not deleterious. The “bladder-wrack” was formerly useful for the production of soda.

Fig. 820.—Bladder wrack.

Fig. 821.—Lichen.

“The life-history of one of these uni-cellular plants in its most simple form, can scarcely be better exemplified than in the Palmogeœa macrococca, one of those humble forms of vegetation which spreads itself as a green slime over damp stones, walls, etc. When this slime is examined with a microscope, it is found to consist of a multitude of green cells, each surrounded by a gelatinous envelope; the cell which does not seem to have any distinct membranous wall is filled with granular particles of a green colour, and a ‘nucleus’ may sometimes be distinguished through the midst of these. When treated with tincture of iodine, however, the green contents of the cell are turned to a brownish hue, and a dark-brown nucleus is distinctly shown. Other cells are seen, which are considerably elongated, some of them beginning to present a sort of hour-glass contraction across the middle; in these is commencing that curious multiplication by duplicative subdivision which is the mode in which increase nearly always takes place throughout the vegetable kingdom.”[37]

Lichens are numerous, and may be found upon the bark of trees in dry forms of grey and yellow growth, and on walls and old stones in our graveyards. On the hills we find them growing upon the granite, and it would appear that they prefer stone to any other holding ground. The Arctic lichens form the principal food of the useful reindeer, and “Iceland moss” is represented as wholesome for man. Lichen is derived from the Greek term for “wart.”

The Fungi are very important, and with them we will close our summary. They include the favourite mushrooms and poisonous toad-stools, with many other “fungous growths,” from the “mould” on the jam pot to the mushroom.

Fig. 822.—a a, Mould from an old bone; b, Mould from jam.

Some of these fungi are peculiar to the substances upon which they exist, and are in numerous instances destructive. The microscopic fungus Puccinea graminis is the parasite which fixes itself to corn, and produces the disease known as mildew, and the Uredo segetum (another microscopic fungus) causes the “smut”; the “bunt” is caused by the Uredo fœtida, and the “spur” or “ergot,” which attacks rye, is caused by the Acinula clavis. These fungi completely destroy the grain of corn in which they form, and propagate in the most rapid manner; the ergot is moreover a dangerous poison to those who eat the bread made of rye infected by it. The truffle is a kind of underground fungus, and is esteemed a dainty. Mushrooms are also fungi, and several species are sufficiently wholesome; these are the field mushroom and the fairy-ring mushroom.

Any organic substance will shortly become covered with this “mould” or mildew. The air is so full of the germs of animal and vegetable life that, as it penetrates everywhere, the smallest supply must contain some germs; and these, under a powerful microscope, present most beautiful forms and colours. We annex (fig. 822) some of these forms highly magnified. They are deposited by the air, and the substance into which they happen to fall determines the kind of life which is to inhabit it. A few of these spores only come to maturity.

We again take the liberty to quote Dr. Carpenter on this subject. He says:—

“There are scarcely any microscopic objects more beautiful than some of those forms of mould or mildew which are so commonly found growing upon the surface of jams and preserves, especially when they are viewed with a low magnifying power and by reflected light; for they present themselves as a forest of stems and branches of extremely varied and elegant forms, loaded with fruit of singular delicacy of conformation, all glistening brightly on a dark ground.

“The universality of the appearance of these simple forms of fungi upon all spots favourable to their development, has given rise to the belief that they are spontaneously produced by decaying substances, but there is no occasion for this mode of accounting for it, since the extraordinary means adopted by nature for the production and diffusion of the germs of these plants adequately suffices to explain the facts of the case.

“The number of sporules which any one fungus may develop is almost incalculable; a single individual of the “puff-ball” tribe has been computed to send forth no fewer than ten millions. And their minuteness is such that they are scattered through the air in the finest possible dust, so that it is difficult to conceive of a place from which they should be excluded.”

Fig. 823.—Eatable mushroom (Agaricus campestris).

Fig. 824.—Seeds with pappi.

Pure water exposed to the air does not afford nourishment to the germs which fall into it, till a sufficient number of them shall have been deposited to form a food for those which come after them; but if we mix with the water any soluble vegetable or animal matter, in a short time the microscope will detect the growth of the germs that are being deposited, for where nourishment is, there only can they be developed. These germs are capable of existing for an indefinite period, either floating in the water, or blown about by the air, and have been detected hundreds of miles from land; the rigging and sails of ships far away from shore are often covered with what sailors suppose to be sand blown from the land, but which are organic substances, either vegetable or animal. According to Humboldt, the Red Sea has derived its name from the fact that at certain seasons the surface of the water has a reddish appearance, and this (as he says) he was fortunate enough to observe, which colour he found to be due to myriads of red fungi, which had formed on the surface. The seeds of some plants are furnished with minute wings or plumes, which cause them to be borne on the air or floated on the water (fig. 824), to fertilise some barren spot, perhaps a coral reef, which has at length reached the surface of the water, and which ascends no higher, for the little creatures which built it are aquatic, and cannot live exposed to the air; this coral reef now becomes a receptacle for seaweed and fungi, which float on the surface of the ocean are washed on to the reef, die, decay, and leave behind a thin layer of mould, which process being repeated again and again, forms an elevated edge to the reef, enclosing a lake, or “lagoon” as it is called, the waters of which evaporate, and the space is filled up in the same way as the edge was formed, together with the excrements of birds, etc., forming layer after layer of mould, and the surface becomes fit for the growth of larger seeds, as the cocoa-nut, banana, etc., which are drifted on to it by the waves; in this way a coral reef becomes an island fit to be inhabited by man and other animals.

It is impossible for any person not accustomed to observe the manner of the propagation of the fungi, to understand a written description, for the fructification of these plants are very varied in the manner of the development of the spores. They are not generally hurtful, but much caution should be observed in the matter of the mushroom, which may be distinguished by the pale pink and black of the under part. There are many poisonous fungi, but the greater number are harmless, though they are not intended for food. They simply clear away the decaying growths, and act as safety-valves to Nature by carrying away what is not required, to give it to the air again to be renewed into life.

The vegetable kingdom forms the link between the minerals and the animals. The vegetable derives food and nourishment from water, carbonic acid, and ammonia, which are, as we already know, made up of certain elements, and thus supply us all with food. They give out oxygen for the use of animals, and are thus, in another sense, the source of life. The growth of a plant is very interesting, and we may conclude by following it.

The seed is sown, and the cells of the “cellular tissue” become developed, passing some upwards, some downwards, to form a radicle or plumule, as explained. The latter carries up the cotyledon, which begins to decompose carbonic acid from the atmosphere, and fixing the carbon as woody fibre. The leaves are then formed and more fibres, and so on for every leaf; thus the number of woody fibres which form the trunk of a tree is in proportion to the number of leaves which that tree has borne, from which we come to the conclusion that the size of the trunk of a tree is the sum of all its branches. While all this is going on, the cellular tissue of the downward part or radicle also becomes developed and divides out into roots, on the surface and at the extremities of which are minute cellular bodies called “spongioles” (from their power of absorbing moisture), which take up the fluid of the earth which surrounds them; this moisture ascends through the vessels of the plant till it arrives at the surface of the leaves, where it is exposed to the action of light and sunshine. The ascent of the moisture of the earth was first correctly explained by Du Trochet, and is owing to a peculiar power which he discovered, and which is called “Endosmose”; this consists in the tendency which a fluid has to penetrate a membrane on the other side of which is a fluid of greater density than itself. This may be seen by the following experiment: obtain a piece of glass tubing about a foot long, having the end blown out into the form of a bell, as in fig. 825, tie a piece of bladder over the expanded end and fill it partly with syrup or gum-water, so that this shall rise in the stalk about an inch; place this in a glass of water with the bladder downwards, and the fluid will be seen slowly to rise in the stalk, so that in perhaps an hour it will rise to the top. This apparatus resembles one of the spongioles at the extremity of the fibre of a root.

Fig. 825.—Endosmose.

The rain falling through the air carries with it a certain amount of carbonic acid and ammonia, which the air always contains, and it is the whole source of the nitrogen which forms a very important part of the bodies of plants and animals. When the rain arrives at the surface of the earth, it sinks down into it and carries with it all soluble vegetable or animal matter which it meets with, together with any soluble earthy matter which may exist in the soil; this forms the sap of the tree. When it arrives at the surface of the leaf, the watery part of it combines with the carbonic acid of the air (through the influence of light), and appropriating its carbon, gives out the oxygen; this is the true respiration of plants, and is exactly the reverse of what takes place during the respiration of animals, in which case oxygen is absorbed and carbonic acid given off. The carbon thus retained by the plant combines with the elements of the water to form the solid green substance called chlorophyl, which is the basis of all the tissues of the plant; the ammonia is also decomposed, and its nitrogen combining with the oxygen and hydrogen of the water, and the carbon of the carbonic acid forms those compounds which constitute the most nourishing parts of vegetables, such as albumen, gluten, etc., and of which all the animal tissues are built up, for the production of these organic substances takes place in the vegetable only, animals simply appropriating them for their food. The sap which reaches the leaf is not all converted into chlorophyl, but also into those peculiar juices which are found in plants, some of which contain sugar, some gum, others (as the pine tribe) turpentine, and in the laurel tribe camphor, all of which are substances containing much carbon; moreover the solid wood and bark are deposited from these juices as they descend from the leaf after having been acted on by light (or the actinic power associated with it). Now, as the water, ammonia, and carbonic acid which descend with the rain are from the air, and as the vegetable is formed wholly by their absorption, it may be fairly said that the vegetable kingdom (and therefore the animal) feeds upon the air, and that the trees do not grow out of the earth, but into it.

Classification of Plants.

For the groundwork of the system of classification which universally obtains at present, we are indebted to Linnæus, a Swede, born in 1707. In his classification of plants, Linnæus followed two different methods. In the one, he based his division of plants in classes and orders, upon certain peculiarities in the floral organs. This system, being thus founded on characters taken from certain parts of the plant only, without reference to others, and having something artificial in it, has for that reason been termed the artificial system, but it is now more generally known as the Linnæan system. In the other method, he arranged the plants according to certain general resemblances and affinities, in natural orders or families. This system, which is known as the natural system, has subsequently been much improved.

We use the term species, to designate a number of individual plants, which, in all essential and unvarying characters, resemble each other more closely than they do any other plant; the term genus or kind, to designate an assemblage of nearly allied species, agreeing with one another in general structure and appearance more closely than they do with any other species. Here, too, it must be obvious, that while all parts of the plant may furnish specific characters, the character of the genera are taken exclusively from the parts of fructification.

In the name of a plant both the genus and the species are given. The name designating the genus is called the generic name of the plant, the one designating the species, the specific or trivial name. Thus, for instance, we have the genus Viola, which includes the species Viola odorata, sweet violet; Viola canina, dog violet; Viola tricolor, heart’s-ease.

It is necessary to give the Latin names of plants, as the common name differs, not only in different countries, but even in different parts of the same country.

An assemblage or group of allied genera, agreeing in their general characters, though differing in their special conformation, is called an order or family of plants.

The sunflower, the daisy, the aster, and the dahlia, are, for example, plants of different genera, but which, all of them, belong to the same order or family.

All plants are divided into three primary classes—viz., Dicotyledons, Monocotyledons, and Acotyledons, as has been stated already.

A proper degree of familiarity with the systematic classification of plants is of the very highest importance to the student. A successful pursuit of this branch of the botanical science presupposes a thorough knowledge of the structure and physiology of plants, and requires, moreover, the aid of attentive observation, and also some diligence in collecting and arranging plants.

The Artificial or Linnæan System of Classification.

In this system plants are divided into twenty-four classes; twenty-three of these contain the Dicotyledons and Monocotyledons indiscriminately; the twenty-fourth class contains the Acotyledons.

The first twenty-three classes are founded on the number, position, relative lengths, and connection of the stamens. The twenty-fourth comprises the plants with inconspicuous flowers. Every class is subdivided again into several orders. This division depends, in the first thirteen classes, on the number of the styles; in classes XIV. and XV. on the nature of the fruit; in classes XVI. to XVIII. and XX. to XXII. on the number of stamens; in classes XIX. and XXIII. on the perfection of the flower. In class XXIV. the orders are formed according to natural affinities.

Tabular View of the Linnæan System of Classification.

A.—Flowers Present (Phanerogamia).
	I. Stamens and pistil in every flower (hermaphrodite).
	1. Stamens free.
		a. Stamens of equal length, or not differing in definite proportions.
	Number of Stamens.
		1		Class	1. Monandria.
		2		“	2. Diandria.
		3		“	3. Triandria.
		4		“	4. Tetrandria.
		5		“	5. Pentandria.
		6		“	6. Hexandria.
		7		“	7. Heptandria.
		8		“	8. Octandria.
		9		“	9. Enneandria.
		10		“	10. Decandria.
		11-19		“	11. Dodecandria.
		20 or more	inserted on calyx	“	12. Icosandria.
			inserted on receptacle	“	13. Polyandria.
	b. Stamens of different lengths, two long and two short			“	14. Didynamia.
	Stamens of different lengths, four long and two short			“	15. Tetradynamia
	2. Stamens united by filaments in one bundle			“	16. Monadelphia.
	Stamens united by filaments in two bundles			“	17. Diadelphia.
	Stamens united by filaments in more than two bundles			“	18. Polyadelphia.
	Stamens united by anthers (compound flowers)			“	19. Syngenesia.
	Stamens united with pistil on a column			“	20. Gynandria.
	II. Stamens and pistil in different flowers (unisexual) on the
	same plant			“	21. Monœcia.
	on different plants			“	22. Diœcia.
	III. Stamens and pistil in the same or in different flowers, on the same or on different plants			“	23. Polygamia.
B.—Flowers Absent				“	24. Cryptogamia

Tabular View of Classes and Orders.

Classes.	Orders.		Examples.
I.—Monandria	Monogynia	one style	Hippuris.
One stamen.	Digynia	two styles	Callitriche.
II.—Diandria	Monogynia	one style	Syringa.
Two stamens.	Digynia	two styles	Anthoxanthum.
	Trigynia	three do.
III.—Triandria	Monogynia	one style	Iris.
Three stamens.	Digynia	two styles	Hordeum.
	Trigynia	three do.	Holosteum.
IV.—Tetrandria	Monogynia	one style	Scabiosa.
Four stamens.	Digynia	two styles	Gentiana.
	Trigynia	three do.
V.—Pentandria	Monogynia	one style	Borago.
Five stamens.	Digynia	two styles	Fœniculum.
	Trigynia	three do.	Sambucus.
	Tetragynia	four do.	Parnassia.
	Pentagynia	five do.	Linum.
	Polygynia	six and more do.	Myosurus.
VI.—Hexandria	Monogynia	one style	Lilium.
Six stamens.	Digynia	two styles	Oxyria.
	Trigynia	three do.	Rumex.
	Tetragynia	four do.	Alisma.
	Polygynia	many do.
VII.—Heptandria	Monogynia	one style	Trientalis.
Seven stamens.	Digynia	two styles
	Trigynia	three do.
	Heptagynia	seven do.
VIII.—Octandria	Monogynia	one style	Daphne.
Eight stamens.	Digynia	two styles	Chrysosplenium.
	Trigynia	three do.	Polygonum.
	Tetragynia	four do.	Paris.
IX.—Enneandria	Monogynia	one style
Nine stamens.	Trigynia	three styles
	Hexagynia	six do.	Butomus.
X.—Decandria	Monogynia	one style	Pyrola.
Ten stamens.	Digynia	two styles	Dianthus.
	Trigynia	three do.	Silene.
	Pentagynia	five do.	Lychnis.
	Decagynia	ten	do.
XI.—Dodecandria	Monogynia	one style	Lythrum.
Twelve to nineteen stamens.	Digynia	two styles	Agrimonia.
	Trigynia	three do.	Reseda.
	Pentagynia	five do.
	Dodecagynia	twelve do.	Sempervivum.
XII.—Icosandria	Monogynia	one style	Prunus.
Twenty or more stamens inserted on the calyx.	Digynia	two styles	Cratægus.
	Trigynia	three do.	Sorbus.
	Pentagynia	five do.
	Polygynia	many do.	Rosa.
XIII.—Polyandria	Monogynia	one style	Papaver.
Many stamens inserted on the receptacle.	Digynia	two styles	Pæonia.
	Trigynia	three do.	Aconitum.
	Tetragynia	four do.
	Pentagynia	five do.	Nigella.
	Hexagynia	six	do.
	Polygynia	many do.	Ranunculus.
XIV.—Didynamia	Gymnospermia	four naked seeds	Lavandula.
Two long and two short stamens. Labiate and Personate Flowers.	Angiospermia	seeds in capsules	Linaria.
XV.—Tetradynamia	Siliculosa	broad and short pod (silicula), and style	Capsella.
Four long and two short stamens. Cruciferous Flowers.	Siliquosa	long pod (siliqua); stigma sessile	Brassica.
XVI.—Monadelphia	Pentandria	five stamens	Erodium.
Stamens united in one bundle.	Enneandria	nine do.
	Decandria	ten do.	Geranium.
	Dodecandria	11-19 do.	Malva.
	Polyandria	many do.
XVII.—Diadelphia	Pentandria	five stamens (two above and three below.)
Stamens united in two bundles (one generally containing nine enclosed in a tube, and one free). Papilionaceæ.
	Hexandria	six stamens (three right, three left, or three above and three below.)	Fumaria.
	Octandria	eight stamens (four above and four below, all united at the base.)	Polygala.
	Decandria	ten stamens (one above and nine below, united in a cleft tube surrounding the ovary.)	Pisum, Trifolium, Genista.
XVIII.—Polyadelphia	Pentandria	five bundles (each bundle bearing five anthers = 25 stamens.)
Stamens united in more than two bundles.	Dodecandria	twelve stamens (each bundle bearing three anthers = 36 stamens.)
	Icosandria	many stamens in bundles, inserted on the calyx (20 stamens in bundles bearing an unequal number of anthers.)	Citrus.
	Polyandria	many stamens in three, five, and nine bundles, inserted on the receptacle.	Hypericum.
XIX.—Syngenesia	Polygamia æqualia, florets all hermaphrodite.		Lactuca.
Five stamens, filaments free, anthers united, flower monopetalous, florets united on a disc. Compositæ. In the first four orders only a common calyx.
	Polygamia superflua, florets of the disc hermaphrodite, those of the ray pistilliferous and fertile.		Aster.
	Polygamia frustranea, florets of the disc hermaphrodite, those of the ray neutral.		Helianthus.
	Polygamia necessaria, florets of the disc staminiferous, of the ray pistilliferous		Calendula.
	Polygamia segregata, a common calyx including all the florets, and a separate involucre for each.		Echinops.
	Monogamia, anthers united, flowers not compound.
XX.—Gynandria	Diandria	two anthers	Orchis.
Stamens and pistil united.	Triandria	three do.
	Tetrandria	four do.
	Pentandria	five do.
	Hexandria	six do.	Aristolochia.
	Decandria	ten do.
	Dodecandria	11-19 do.
	Polyandria	twenty or more do.
XXI.—Monœcia	Monandria	one stamen	Arum.
Stamens and pistils in different flowers on the same plant.	Diandria	two stamens	Lemna.
	Triandria	three do.	Carex.
	Tetrandria	four do.	Urtica.
	Pentandria	five do.	Amaranthus.
	Hexandria	six do.
	Heptandria	seven do.
	Polyandria	more than seven do.	Quercus.
	Monadelphia	stamens united	Pinus.
	Syngenesia	stamens united by their anthers.
	Gynandria	stamens and styles united
XXII.—Diœcia	Monandria	one stamen	Salix.
Stamens and pistils in different flowers on different plants.	Diandria	two stamens
	Triandria	three do.	Ficus.
	Tetrandria	four do.	Viscum.
	Pentandria	five do.	Cannabis.
	Hexandria	six do.	Loranthus.
	Octandria	eight do.	Populus.
	Enneandria	nine do.	Laurus.
	Decandria	ten do.
	Dodecandria	11-19 do.	Stratiotes.
	Polyandria	many	do.
	Monadelphia	stamens united in one bundle.	Juniperus.
	Syngenesia	stamens united by	the anthers.
	Gynandria	stamens and styles united.	united.
XXIII.—Polygamia	Monœcia, hermaphrodite, staminiferous, and pistilliferous flowers on the	same plant.	Acer.
Stamens and pistil in the same, or in different flowers, on the same or on different plants.
	Diœcia	on two plants	Fraxinus.
	Triœcia	on three plants
XXIV.—Cryptogamia	Filices	Ferns	Aspidium.
Organs of fructification concealed (flowers inconspicuous).	Musci	Mosses	Spagnum.
	Hepaticæ	Liverworts	Marchantia.
	Lichenes	Lichens	Cetraria.
	Algæ	Seaweeds	Fucus.
	Fungi	Mushrooms	Agaricus.

With all its imperfections, the artificial system has this advantage, that the character on which it is founded is sufficiently conspicuous (that is, of course, with the plants in full flower) to render it generally easy to ascertain the class and order of a plant. At all events, it may serve as a useful artificial key, and as such may be combined advantageously with the natural system.

114. Natural System (Jussieu’s).

Classes.
I.	Acotyledons				1st	Class.
II.	Monocotyledons
		Mono-hypogynæ (stamens hypogynous)			2nd	”
		Mono-perigynæ (stamens perigynous)			3rd	”
		Mono-epigynæ (stamens epigynous)			4th	”
III.	Dicotyledons.
		Monoclines, flowers hermaphrodite.
		Apetalæ (no petals)
			Epistamineæ (stamens epigynous)		5th	”
			Peristamineæ (stamens perigynous)		6th	”
			Hypostamineæ (stamens hypogynous)		7th	”
		Monopetalæ (petals united).
			Hypocorollæ (corolla hypogynous)		8th	”
			Pericorollæ (corolla perigynous)		9th	”
			Epicorollæ (corolla epigynous)	Synantheræ (anthers united)	10th	”
				Chorisantheræ (anthers free)	11th	”
		Polypetalæ (petals distinct)
			Epipetalæ (petals epigynous)		12th	”
			Peripetalæ (petals perigynous)		13th	”
			Hypopetalæ (petals hypogynous)		14th	”
	Diclines, flowers unisexual, or without a perianth.				15th	”

This system, being likewise founded partly on individual organs, is also, to a certain extent, artificial; and, strictly speaking, every natural method of botanic classification must partake more or less of an artificial character, as many orders of plants merge so insensibly into others that their respective limits cannot be accurately or rigorously defined.

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CHAPTER LIV.
ZOOLOGY.

CLASSIFICATION OF ANIMALS—VERTEBRATES AND INVERTEBRATES—PROTOZOA—HYDROZOA—ACTINOZOA.

Zoology treats of life—of organized beings which are capable of voluntary motion. Plants exist, animals live and move. Both are organic beings, but the latter possess the faculty of will and spontaneous movement. The animal can leave a place and enjoy other surroundings, the plant cannot. We have already crossed the borderland which connects the plant and the animal. We have seen plants almost animals. We could commence this section with animals which are almost plants, so closely do the divisions approach each other. Zoology is the science of the knowledge of animals as Botany is of the knowledge of plants.

Fig. 826.—Echinus, or Sea-Urchin.

Where there is vegetation there are animals, not quadrupeds or bipeds necessarily, but numbers of small, it may be invisible, creatures which exist upon the vegetable kingdom—the algæ and minute creations of globules and cells, the infusoria already mentioned, the corals, etc. And in the “protozoa,” or first specimens of animal life, we have a similarity to the vegetable kingdom; we then get by gradual steps to other more perfect beings, each after his kind, till we arrive at the most perfect animal—Man.

Animals are divided into two families, the Invertebrate and the Vertebrate. The former has no spine nor skeleton; the latter has both. These again are divided into sub-families, classes, and orders, as follows.

Man is an animal—but what is an animal? We can scarcely tell in a few words. Linnæus defined the difference between the animal and the plant, for the former, said he, live, grow, and feel, while the latter live and grow. We have protozoa in the animal kingdom consisting of a single cell or blood corpuscle, some others without mouths or digestive organs, some have no head; some, as in the tape-worm, only a so-called head, with suckers or attachments, after which it develops joints, which are at first imperfect, but gradually mature as they are pushed farther away by new-issuing joints.

Animals, therefore, do not all possess organs, nor is there any common organ by which all animals can be classed. The indispensable in one is absent in another, and while our mouths and digestive apparatus are all important, in other animals suckers and no digestive apparatus at all is quite sufficient. Some have one mouth, some several; some have mouths and a proboscis to assist them, some only the trunk and no mouth—so called—at all, as in some insects.

Fig. 827.—Polypidom.

The organisms which could not be distinguished from vegetables were termed zoophytes, or plant animals, and, were space available, a comparison might be instituted between the extremes of growth of the animals and plants, from the largest whales to the tiny microscopic protozoa, and from the mould upon jam to the gigantic trees of California, one leaf of which it is said will shelter twenty men from rain.

Cuvier spent many years in perfecting his systematic arrangements of animals, and this classification, though many rearrangements have been made as modern discovery progressed, may be regarded as the fundamental system of all. Professor Agassiz adopted it with modifications. Professor Nicholson has made a somewhat different arrangement, but essentially there will be found but slight difference between them. We append both these arrangements for comparison:—

Agassiz-Cuvier.
INVERTEBRATA.
Branch I.—Radiata.
Class I.—Polypi	2 orders	Including actinoids and halcyonoids.
Class II.—Acalephs	3 orders	hydroids, discophoræ, ctenophoræ.
Class III.—Echinoderms	4 orders	crinoids, asteroids, echinoids.
Branch II.—Mollusca.
Class I.—Acephala	4 orders	bryoza, brachiopods, tunicata, and lamellibranchiata.
Class II.—Gasteropoda	3 orders	pipteropoda, heteropoda, and gasteropoda (proper).
Class III.—Cephalopoda	2 orders	tetrabranchiata, and dibranchiata.
Branch III.—Articulata.
Class I.—Worms	3 orders	trematods (including leeches, etc.), nematoids, and annelides.
Class II.—Crustacea	4 orders	rotifera, crinopods, tetradecapods, and decapods.
Class III.—Insects	3 orders	myriapods, arachnoids, and insects proper.
Branch IV.—Vertebrata.
Class I.—Myzontes	2 orders	myxinoids and cyclostomes.
Class II.—Fishes proper.
Class III.—Ganoids	3 orders	cælacanths, axipenseroids, and sauroids.
Class IV.—Selachiens	3 orders	chimæræ, galeodes, and batides.
Class V.—Amphibians	3 orders	cæciliæ, ichthyodi, and anoura.
Class VI.—Reptiles	4 orders	serpents, saurii, rhizodontes, and testudinata.
Class VII.—Birds	4 orders	natatores, grallæ, rasores, and incessores.
Class VIII.—Mammalia	3 orders	marsupiaia, herbivora, and carnivora.

In the vertebrated animals the blood is red in consequence of the minute cells (corpuscles) which contain the colouring matter. In invertebrate animals these red cells are absent, and so the animals are white-blooded. Some animals, again, are cold-blooded like the fish; birds and mammalia have warm blood. It is worthy of remark that the higher we advance in the scale the fewer the offspring of the animal. The animalcules multiply at the rate of many billions a day, and even one codfish is stated to contain more than nine millions of eggs. A mackerel will produce 500,000; and so on, as we rise, we find mammals with seldom more than ten young at a time, down to one single offspring.

We could fill pages with the account of the differences existing between animals created for such different purposes and fitted to inhabit different climates, their mode of feeding and catching prey. The manner of bringing forth and rearing the young, and the temperament and temper of the animal creation would fill a volume, but we cannot now stay to examine these various characteristics. The following is the arrangement now usually adopted:—

Nicholson.
INVERTEBRATES.
Protozoa.
The lowest forms of animal life—microscopic animals.
Gregarinida	Cell forms; worm-like.
Rhizopoda	Amebæ, foraminifera, radiolaria, sponges.
Infusoria.	Suctoria, ciliata, etc.
Cælenterata (The Old Radiata).
HYDROZOA.
Intermediary, having a mouth and receptacle separated by no alimentary canal.
Polypes and Zoophytes, Actinozoa.	Medusæ, millipores, corals, sea-anemones, tubipora, siphonophera, etc.
Echinodermata.
Star-fishes, sea-urchins, sea-cucumbers, and crinoids.
Annulosa.
Entozoa	Tape-worms, etc.
Rotifera	Wheel-Animalculæ.
Annelida	Worms, leeches.
Cerripida	Barnacles.
Crustacea	Shell-fish.
Insecta	Various insects.
Arachnida	Spiders, scorpions, etc.
Mollusca.
MULLOSCOIDA—POLYZOA.
Acephala of headless pupa.	Encephala with head.
Tunicata	Pteropoda.
Brachiopoda	Gasteropoda (univalves).
Lamellibranchiata (bivalves).	Cephalopoda, cuttle-fish, etc.
VERTEBRATA.
Ichthyopsida.
Class I.—Fishes	Various orders.
Class II.—Amphibia	Frogs, toads, salamanders, etc.
Sauropsida.
Class III.—Reptilia	Tortoises, smaller snakes, lizards, etc.
Class IV.—Birds	Various orders.
Mammalia.
Class I.—Non-Placental	Marsupials.
Class II.—Placental	Edentata, cetacea, ungulata, quadrumana, bimana, etc.

We will adopt the latter order as being the more modern, and endeavour to make the various classes of the invertebrates clear to the mind, if we cannot present them to the vision, of the reader.

In our sketch of Botany we remarked upon the similarity existing between the cells of plants and animals, and although there are, of course, differences, there are many points of resemblance in these cells.

Plants have their lowest representatives called Protophytes. Animals which correspond to this class are termed Protozoa, from the Greek, proton, first, and zoön, animal. The former are, as already mentioned, seen amongst the algæ, consisting of simple cells, and protozoa cannot easily be distinguished from them except in the matter of nutriment, for some protozoa have no mouth except in the infusoria class. The cells are very much alike, and Dr. Carpenter sums them up briefly as follows:—

“The animal cell, in its most complete form, is comparable in most parts of its structure to that of the plant, but differs from it in the entire absence of the ‘cellulose wall’ or of anything that represents it, the cell-contents being enclosed in only a single limitary membrane, the chemical composition of which, being albuminous, indicates its correspondence with the primordial utricle. In its young state it seems always to contain a semi-fluid plasma, which is essentially the same as the protoplasm of the plant, save that it does not include chlorophyl granules, and this may either continue to occupy its cavity (which is the case in cells whose entire energy is directed to growth and multiplication), or may give place, either wholly or in part, to the special product which it may be the function of the cell to prepare. Like the vegetable cell, that of animals very commonly multiplies by duplicative subdivision, it also (especially among protozoa) may give origin to new cells by the breaking up of its contents into several particles.”

Fig. 828.—Animalculæ found in stagnant water.

a, Cyclops Quadracornis.	f, Ambœba princeps.
b, Anguillula. Fluviatillis.	g, Acineta mystacina.
c, Actinophrys. Sol.	h, Oxytrycha.
d, Coleps Hirtus.	i, Triophthalamus dorsalis.
e, Vorticella.	j, Polyarthra.

The protozoa are microscopic creatures consisting of one or more cells, and are infinitely little, thousands existing in a drop of water. They have no distinction of sexes, and their generation takes place by subdivision or blending of cells. The infusoria are the highest of the protozoa, and were formerly included amongst the radiata. Their numbers are infinite, and in a drop of water (see fig. 828) some very interesting specimens will be found. These infusoria are merely sarcode, or a jelly-like substance, and some have cilia, or hairy appendages, with which they agitate the water and cause a kind of current which brings them food. It is this partaking of food which has served to divide the lowest animal from the lowest vegetable creations. There is no progressive increase of development from the lowest plant to the highest animal. The animal begins by himself, as it were, as the plant, and both grow up in different directions. The protozoa exist upon organic substances, while plants absorb inorganic substances and assimilate them.

The Gregarinidæ are very tiny cells, and though microscopically minute, they sometimes develop into worm-like or elongated oval bodies. They inhabit the intestines of crustacea, worms, and cockroaches, as well as of higher animals. They are capable of certain motion, but are not furnished even with the “false feet” (pseudo podia) of the rhizopoda, the next animal in these very low scales of creation.

Of the Rhizopoda the Amebæ are very interesting, and we find them in our veins as well as in the stagnant green water of the pond. They are simply sarcode or jelly, and, as the name implies, the amebæ can change their appearance (amoibos, changing). They possess a kind of crawling, progressive motion, and under the microscope will be perceived to develop a tiny bud, as it were, which is the “false foot” that assists its progress. These amebæ are in our blood moving about, and are always altering their form, and when warm they move more quickly in the red blood corpuscles or cells, but excessive heat will kill them.

These curious creatures feed by the foot they protrude; and by drawing in the “process” as it is termed, they can collect within themselves the nourishment they require. Of course they have no mouth, and if we can conceive a creature of this kind which thrusts out from a jelly-bag a tiny lump, and pulls it in again at any time and place it likes, we have an idea of an ameba.

The pond ameba is somewhat different from the others, inasmuch as it possesses an outer and inner portion or layer which are different in density. There is what is termed a contractile vesicle which “beats” as a heart beats, but this is very primitive. There is really no structure whatever in these rhizopoda, and, as we have seen, their shape is always undergoing change. The outer and inner layers of the amebæ are called “the ectosarc” and “endosarc” respectively; the latter contains the darker portion—the nucleus.

The Foraminifera have already been mentioned in the chapters on Geology. We find these minute creatures must have had a great deal to do with the building up of rocks, as they have the power to make tiny coverings for themselves, which have been built into rocks by the addition of sandy particles, and consolidated by pressure. Here we have a most wonderful instance of the tiniest creatures producing the greatest masses of the earth. The body is merely sarcode, the shell is carbonate of lime. The foraminifera produce false feet in abundance, which surround the cell like fine hairs or rays. They live in the sea, and when they die the shells descend upon the ocean floor, where they undergo many changes and become converted into rock. The ooze of the great oceans is composed of these shells, and is practically a chalky deposit; the shells are being built up as in former ages with the curious nummulites of the Eocene formation, which are amongst the most interesting of fossils.

Sponges. We must go on at once to the Sponges, which form such an interesting subject as they are so familiar to us all. Sponge is not often regarded by the public as an animal, and though perhaps authorities may not have yet concluded in what category they should be placed, we may consider them here according to the list.

We find the spongida both in fresh and salt water, and they have given rise to much discussion as to whether they should be classed as animals at all. But that question having been finally settled, we can proceed to examine a sponge in its native state, and we shall find both skeleton and “flesh.”

The skeleton is hard and composed of needles of “tiny” texture. The flesh is “sarcode,” and the animal possesses no mouth, but is full of holes (pores) and canals through which the water is continually distributed. The outer layer of the sponge is formed of ultimate components of the living substance of the sponge (like the amebæ we have been considering). Each contains a nucleus, and when joined together form the outer layer of the body. Beneath is a wide cavity communicating with the exterior by means of minute holes, and filled with water. The cavity separates the superficial layer from the deeper substance, which is of the same character. In the water passages of the sponge are cilia which induce a cement, and the interior canals develop into chambers lined with sponge particles, and the water carries particles to the sponge, which represents a kind of sub-aqueous city, where the people are arranged about the streets and roads in such a manner that each can easily appropriate his food from the water as it passes along.[38]

Fig. 829.—Fragment of sponge (magnified).

Sponge, then, is a mass of living organisms—tiny living creatures capable of feeding and of movement, resembling amebæ or perhaps infusoria, with cilia, to enable them to obtain nourishment by a kind of inhalation or respiration. They are reproductive by sexual and a-sexual processes which produce spongellæ. The living sponge is a beautifully coloured animal, and grows upon almost any solid foundation; and in the autumn the parent sponge displays a number of yellow dots or “gemmules,” which are the young. These are soon cast off and left to shift for themselves, and seek their fortunes, helpless as they appear, in the wide and stormy sea. At last they find a resting-place, and fix themselves for ever, growing up and reproducing their species until they are carried off to be sold and used in civilized countries for domestic purposes.

We must leave these curious animalculæ and glance at the Infusoria, which constitute a higher branch, but microscopic and universal, and include those called Flagellate, Ciliate, and Tentaculate. The first have whip-like cilia, or feelers, or filaments, which are ever in motion to cause a movement of the water and carry food to the animal. You will find plenty of infusoria in any stagnant water, and when placed under the microscope a mouth may be perceived, but no stomach, nor any apparent receptacle for food, which appears to enter at once into the body substance. The other kinds capture their food by seizure by the tentacles, or by agitating the cilia, like the flagellata, and thus whipping the nourishment towards the mouth, as children will draw in a toy boat to land by agitating the water in the given direction. These cilia, or hairs, serve for organs of locomotion as well as of capture. These creatures are called Infusoria, because they exist in vegetable “infusions” exposed to the atmosphere.

Fig. 830.—Structure of polypidoms.

Decaying vegetable or animal substances, such as the leaves of trees, grass, a piece of flesh, etc., affused with water and exposed to air and warmth, will speedily, upon microscopic examination, be found peopled with numbers of most active minute creatures of the most varied forms. These animalcules are found also in the stagnant pools around our cities, in the waters of rivers, harbours, and lakes, and even in the ocean.

In reference to the origin of these animalcules, the view was long entertained that they were generated spontaneously, that the decaying vegetable and animal substances were decomposed and resolved into these simple beings. More accurate experiments have shown, however, that the infusoria are produced from ova, or germs, which are probably carried about in the dried-up state, in the form of minute particles of dust,[39] ready to develop themselves in any spot which may afford them the requisite moisture and nutriment. In this respect they resemble the microscopic fungi, whose germs are diffused in the same way. When once they have obtained the means of development, they multiply with incredible celerity. If the decaying vegetable or animal substances be carefully excluded from contact with the air, or if the air be heated before it is admitted to them, no infusoria will appear. They are rarely developed on mountains of a certain height, where the atmosphere is free from foreign bodies.

Fig. 831.—Volvox globator.

Though these animalcules are so exceedingly minute, yet the forms exhibited by them are extremely various, and some of them present also considerable variety in the forms assumed by the same individual under different circumstances. In many species the soft body is enclosed in a firm integument, strengthened by a deposit of siliceous matter; these envelopes, which are often preserved after the death of the animals, are termed the shields, and the animalcules encased in them are called loricated infusoria. The remarkable discovery has been made that large distinct beds of former formations are entirely made up of the accumulated remains of these animalcules.

We arrive at the Hydrozoa after leaving the Infusoria, and find ourselves in the sea, and far from land, where it will be difficult for us to ascertain the characteristics of these interesting animals. But fortunately we can obtain much nearer home, and occasionally in a private aquarium, a specimen of the hydrozoa which will serve our purpose, as it has served before to introduce readers to the study of these water-polypes, some of which are so like plants that they are frequently mistaken for them.

The hydrozoa present a “definite histological structure,” says Professor Huxley; “the body always exhibits a separation into at least two distinct layers of tissue, an outer and an inner.” The Hydras, or fresh-water polypes, which may be found in nearly every pond adhering to the duckweed, appears like tubes, and if touched will curl up into tiny knobs. But if let alone they will adhere to a glass by their single foot, or sucker, which can be moved at pleasure.

Fig. 832.—The hydra.

The foot, or sucker, is continued to a slender cylindrical stalk, from the end of which radiate a number of tentacles, or “feelers,” growing around the mouth, and serving to convey or attract food to the animal which is, so to speak, all stomach. There is no breathing apparatus, and what food it cannot digest is expelled from the mouth. The peculiarity which has given the hydra its name is, that no matter into how many pieces you cut this polype, the parts cut off will all develop into little polypes perfect as their parent.[40] But germination is carried on naturally by buds thrown out, and cast (by “gemmation”), or by the ordinary sexual production of ova.

The outer and inner skins of the hydra are called the ectoderm and endoderm, and the animal is quite capable of locomotion, walking, or rather moving, backwards, by raising and planting its sucker or foot, and by swimming. The prey is captured by the tentacles and by the darting out of tiny spears from the cells or “thread cells” which contain them on the surface of the body. The well-known “Portuguese man-of-war,” an ocean polype, has these “harpoons” greatly developed, and can inflict serious pain as of many stinging nettles; the sensation is exceedingly painful, and lasts some time.

Fig. 833.—Medusa.

The Medusidæ are known to the seaside visitor as the jelly-fish, and the other Acalephæ, the “hidden-eyed” medusæ, include the Portuguese man-of-war mentioned above, and many other umbrella-like animals. They have received the name of medusæ from Medusa, whose long, snaky locks the tentacles of the animals are supposed to be like. Some of these “floating umbrellas” are very dangerous, and will inflict severe stings upon any one in their vicinity. The tentacles or filaments extend for a long distance, and bathers should be cautious. We have often watched them, and they are beautiful to contemplate particularly at night, and in Kingstown Harbour, near Dublin, many exceedingly fine specimens have been obtained. The pulsation of the “umbrella” or bell, enables the animal to swim, and the even undulations of this beautiful covering are apparently caused by nervous contractions.

The jelly-fish have no resemblance to “fish,” and scarcely appear to exist; they are of no use to man, and when removed from the water dwindle by little and little to a tiny film and nothing more—they dissolve into air and water. Cases have been known and tales told of how farmers collected hundreds of these jelly-fish for manure, and when the cart reached the field, to the man’s astonishment, nothing was left but what appeared cobweb in the place of the load of fish.

The Cyclippe is a very common specimen, and moves by means of its cilia; Cestum Veneris—the zone or girdle of Venus—is another curious example. It appears like a glass ribbon about five inches wide and perhaps four or five feet long. The cilia when in motion are very brilliant in colouring, and the creature undulates through the water in a remarkable manner.

The luminosity of the medusæ is clearly perceived, the so-called phosphorescence being due chiefly to the minute jelly-fish which abound near the surface of the sea. It appears impossible, for most, at any rate, if not all, these medusæ to sink beneath the surface, for they can be found in hundreds cast ashore, melting away into film. We might imagine that they would be provided with some means of sinking themselves, but being apparently only air and water, it is necessary for them to remain upon the surface to exist at all.

Fig. 834.—Sea cucumber.

The term Acalephæ, by which they are known, means “stinging” fish or sea-nettles, the Greek word meaning nettle.

The Actinozoa comprise corals and the popular sea anemones (actinidæ). They resemble the hydrozoa in possessing tentacles, and also the two inner and outer tissues of the body. But they differ from the hydrozoa in their interior arrangement in the possession of a kind of stomach between the “body cavity” and the mouth which the hydrozoa do not possess. The appearance of the sea anemone is well known. It fixes itself by the flat base and hangs out its tentacles to obtain food. When we touch an anemone with a stick we perceive how it contracts itself, but there is no nervous system nor any respiration. The reproduction of its species is carried on within, not as in other animals, like the hydra, by exterior budding.

Fig. 835.—Coral.

The corals belong to the same class as the sea anemones, and are called zoanthidæ. We have already in previous portions of this volume mentioned the “coral” building polypes, but we may again describe them here. We have the black coral or antipathidæ, which live in masses and are united by a stem. They grow upon this fleshy trunk and cover it in time “just as a trunk of a tree is covered by the bark.” This stem is called a cænosarc, which secretes the coral, or skeleton. The madrepores are the greatest producers of the coral of commerce.

Fig. 836.—Coral.

“If we examine a simple coral of this group,” says Professor Nicholson, “we find that we have to deal with an animal in all important respects identical with an ordinary sea anemone, but having a more or less complicated skeleton developed in its interior.” This skeleton is the corallum, and it is composed, as most people are aware, of calcareous matter deposited within the polype itself; in the former case the development or formation is exterior to the polype. A single polype will thus secrete a deposit, and a colony of them produce a compound skeleton, and as they throw out buds or young polypes, the manufacture of skeletons goes on by secretion.

The Tubipores are like pipes, and the coral has been termed the “organ-pipe.” It is formed cylindrically and joined externally. As under Geology we have examined the question of coral reefs, we need not here recapitulate the descriptions given in that section.

Fig. 837.—Coral.

Doctor Bariel writes of these animals as follows:—“By far the greater part of the Zoanthoid polypes, as they grow, deposit in the cellular substance of the flesh of their back an immense quantity of calcareous matter which enlarges as the animal increases in size, and, in fact, fills up those portions of the substance of the animal, which by the growth of new parts are no longer wanted for its nourishment, and in this manner they form a hard and strong case, amongst the folds of which they contract themselves so as to be protected from external injury, and by the same means they form for themselves a permanent attachment which prevents their being tossed about by every wave of the element in which they live. The stony substances so formed are called corals, and their mode of formation causes them exactly to represent the animal which secretes them. The upper surface is always furnished with radiating plates, the remains of the calcareous particles which are deposited in the longitudinal folds of the stomach.”

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CHAPTER LV.
ECHINODERMATA—ANNULOSA—ENTOZOA—INSECTA.

SEA-URCHINS—STAR-FISHES—FEATHERY STARS—SEA-CUCUMBERS—WORMS—LEECHES—ROTIFERS—TAPE WORMS—INSECTS.

The Echinodermata or spiny-skinned, are most commonly represented by the sea-urchins and star-fishes of our coasts. In some of the classes locomotion is performed by means of these spines or prickles, which serve as legs. In others, movement is carried on by suckers and tubes as in the star-fishes, these tubes being also the means whereby the animal obtains its food.

Fig. 838.—Sea-urchin (echinus), with and without spines.

They have a digestive system, and possess a curiously horny skin even when spines are absent. The mouth is in the centre. We give an illustration of the sea-urchin, and of a section of a spine, which is a beautiful object when seen under the microscope, for these spines can be made quite transparent when cut across and ground. The shelly covering is porous, and as the animal grows the shell is added to at the edges. Underneath will be found the mouth, which has teeth fitted for devouring the small crustacea. These sea-urchins abound, and their porous shells may be picked up frequently after a storm.

The star-fishes are well known to all searchers amongst the rocks and those who study the shore, and are often taken home for an aquarium. They are very voracious, however, and when one is examined in a glass of sea-water, the observer will detect many suckers protruding from each of the rays. It is by means of these suckers, which are put forth from innumerable little holes called “ambulacral apertures,” that the star-fish makes his way up the rocks and along the ocean bed. The stomach of the star-fish is extensive, and situated in the centre of the rays wherein is a digestive apparatus. The rays are composed of detached but beautifully fitted pieces, so united as to be flexible, and around the mouth and in strong frame-work. The star-fish has no teeth, but manages to dispose of a vast quantity of matter, which if left alone would be injurious in decay.

Thus Nature has provided a shore scavenger to devour what would be harmful, just as the vulture on land eats the carrion. Besides this kind of refuse food, the star-fish eats small crustaceans, and oysters fall victims to him. By embracing the shell the star-fish manages to insert itself, and if it cannot bring the oyster out to its mouth, it will quietly turn out its mouth into the oyster-shell, and save the bivalve any trouble in the matter. Some writers declare that the star-fish stupefies or poisons its victim, and then the shell opens. These asteroidea can reproduce a ray that has been injured or cut off, or they can break themselves to pieces if caught.

Fig. 839.—Spine of echinus (A, natural size; B, a section magnified).

The brittle stars and feather stars appertain to the order of the Ophiuroida or “serpent-armed,” because the rays are more flexible and thin than the common star-fish. But they differ very much from the star-fish in the arrangement, as well as in the shape of their arms. The former possesses rays which form an appendage of the stomach and enclose it. In the brittle stars the rays are limbs, and could be detached without taking the life of the animal, except in so far as to deprive it of means to obtain its food. The body is quite independent of the rays, the mouth occupying the centre, and is surrounded by minute suckers. The stars are much more flexible than the star-fishes, their rays are longer, and serve either as feet, fins, tentacles, or arms.

The crinoids also belong to the Echinodermata, and resemble plants more than star-fish. They are fixed upon a stalk like a flower, growing upright from the sea-bottom, and the body is called a calyx, which is composed of a ventral and dorsal surface. The arms branch out from the calyx, just as a small tree does, and if we can imagine one of the last planted trees on the Thames embankment reduced to half a finger’s length or less, we have a sort of idea of the crinoid “in the rough.”

A polype supported on a stem branching out in feathery, grassy-looking arms represents the Encrinites, the remains of which are found as fossils. The arms of the crinoids are subdivided, and quite a flowery crown may in time result. The animal obtains its food by the motion of cilia. The stem and the branches are jointed, as it were, and capable of flexible movement in any direction. The crinoids remain stationary during their lives.

The care taken by the star-fish of its young is remarkable. It carries the eggs about in its suckers and with great caution. The young remain attached to the mother until they are able to go about alone, and then the physical attachments die off, and the asteroidea goes forth to seek its fortune in the sea.

The echinus, already mentioned, is a most elaborately constructed animal; the plates being secreted from the soft parts are ever being renewed as the animal gets older and larger. The whole subject is well worth a long independent study, of which it is here impossible for us to give the results.

The sea-cucumbers are more like the familiar garden slug than any other animal, and are surmounted by a fringe round the mouth which looks like leaves. The surface is moist, and has no horny covering like the “urchin,” or star fish, but the suckers are present and are used for locomotion. The tentacles round the mouth serve as prehensile organs. The “alimentary canal” is most curiously curved, and of great length, and the animal can turn itself “inside out” with great facility if alarmed. It possesses a kind of breathing apparatus, and may be classed as the most highly organized of all the Echinodermata. These cucumbers are much esteemed by the Chinese, and “trepang,” as they are called, are caught by thousands in Australian waters.

Annulosa.

The worm-like animals are divided into sections, which include intestinal worms, entozoa, annelida, and crustacea, with the worms, spiders, and insects classed in each section. We may at once perceive what a very extensive division the Annulosa is, and we must devote some space to it.

Fig. 840.—Earth worm (lumbricus terrestris), leech (hirudo medicinale).

The Rotifers, or “wheel animalculæ,” are included in this class; they stand almost alone, and certainly invisible to the naked eye. They are very curious animals, as will be seen from the accompanying illustration. The motion of the cilia around the mouth gives the whirling movement from which their name is derived (fig. 841).

The Annelides, or worms, include earth-worms, water-worms, leeches, etc. The appearance of the earth-worm is so common that few people comparatively studied it until Mr. Darwin’s book took the amateur reader by surprise and delighted him, and to that volume we must refer our readers for details of these very interesting animals, termed annelides because of the rings appearing upon their bodies.

The common leech is well known in medicine. It is curiously enough an inhabitant of ponds and lakes, and in such conditions has no opportunities for tasting the warm blood for which it develops such a liking when opportunity offers. This is really a remarkable fact, that the animal should be placed in a position naturally in which its most natural tendencies should remain unsatisfied.

The progression of the leech is performed by undulating movements and the prehensile action of the suckers—head and tail. The eyes are ten in number, near the mouth and at the top of the head. The mouth is furnished with numerous tri-radiate teeth, but in some leeches they are not sharp, as in the “medicinal” variety. It is known that both sexes are represented in every leech, but they are not self-reproductive.

The earth-worm, so familiar to all, has been lately raised into importance. It lives in clay, and bores its way through the ground. It feeds upon organic matter contained in the earth, and when it has assimilated the nourishing particles, it ejects the remainder in small heaps of soft dirt, which are visible after rain particularly. The worm, by its burrowing, turns up the land, and vastly increases its fertility.

Fig. 841.—Wheel animalcule (rotifer vulgaris).

The earth-worm in its outer structure resembles the leech, but, as any one will at once perceive, the worm is not furnished with suckers by which it can assist itself to move. Instead of these rounded terminals the worm is finely pointed, and thus capable of boring its way through the earth. Progression is accomplished by moving first the head portion and then the next, so that a regular series of movements is necessary. The minute spines or bristles of the worm prevent its body being retracted by muscular effort.

The vital organs are rather forward of the centre of the body, and so if a worm be cut behind them it will survive and reproduce a tail. But the portion cut off will not be found alive, nor is it capable of forming a new perfect worm as generally supposed.

There are many other orders of worms which we can only indicate—viz., the Tubicolæ which surround themselves with a hard case; the Errantia, or sea-worms, sand-worms, etc., like the lobworm used for bait, and the naiads of our fresh-water ponds, all of which are suited to the aquatic life they lead. Indeed, of all the annelides, the earth-worm is the only specimen that is suited for living upon land. As regards the last mentioned, we may add that worms do not prey upon dead bodies as is so generally imagined. They are vegetable feeders, and do not burrow very deeply.

The transparent condition of the Rotifers renders them easy of observation under the microscope, and we find a nervous system, intestines, and a developed stomach. They are fresh-water inhabitants.

The Entozoa or “intestinal” worms claim a brief notice at our hands. The entozoa are those beings which inhabit, as parasites, the intestines and other parts of animals. Their history is still obscure, but there seems to be about twenty varieties of these creatures, and a great number of animals have their peculiar entozoa. The best known in the human subject are the “Ascaris” or thread-worm, the “Lumbricus Teres” or long-worm, and the “Tænia” or tape-worm; this last is jointed, and grows to several yards in length.

The development of these Tænia is one of the most curious performances of nature. Each of the joints shown in the illustration below (fig. 842) is a perfected and mature proglottis, containing the ova or eggs, which can only be brought to perfection when swallowed by a warm-blooded animal (not the same from which they emanated). The head within the embryo then holds to the tissues and penetrates to the alimentary canal, where only it can redevelop joints from the so-called head, which has no organs and merely pushes out immature joints which are continued, and they become more mature the farther they are pushed out by the new ones. The “measles” of the pig are produced by the ova of these worms.

Fig. 842.—Tape worm (proglottides).

Myriapoda.

The “many-footed” annulosa include the centipedes and millipedes, and may be regarded as a connecting link between the worms and the insects. The heads of these animals are distinct from the body.

The millipedes can be any day found under a large stone in a field which has not been tilled, or any place where a stone has been suffered to remain for some time undisturbed. These specimens are of the pill-millipede order, because they roll themselves up into a ball when disturbed. The myriapods of this country are not of large dimensions, but in tropical climates they attain a great size. The giant centipede has been found in South America more than a foot long, and is capable of inflicting severe wounds, its tenacity being extraordinary and equalling that of the bull-dog when once it has gripped its enemy.

The myriapods have no wings; they possess antennæ, and numerous, never less than eighteen, feet,—frequently twenty pairs, but never a thousand, much less “ten thousand” feet, as the class name indicates. They are provided with strong forceps or “foot-jaws,” which supply a poison for killing their enemies. The millipedes and centipedes are known scientifically as Iulidæ and Scolopendridæ respectively, and in most points of internal arrangement resemble insects, such as breathing by spiracles or (stomates), and trachæ or tubes. Some of the centipedes possess electric qualities, and can administer a shock to an opponent.

Insecta.

Insects inhabit the world around us in myriad forms in air and earth and water. Some exist for a very brief space in the air; others live under water, or in trees, or in the ground; some burrow and hide in chinks of rocks and under stones. The numbers are countless, and all have some function to perform as palpably as the busy honey-bee, or as mysteriously as the giddy, careless butterfly.

Fig. 843.—Anatomy of the external skeleton of an insect.

Insects are divided into three distinct parts,—viz., the head, the thorax, and the abdomen, and each of these parts has a pair of legs attached to it, as will be perceived from the accompanying diagram. Along the body are tubes called trachæ,—for insects do not breathe by lungs,—by which the air is carried into the system of the insect, by the “spiracles” or openings of fine network, to prevent dust entering the air-passages. The head is joined to the body by a constricted neck, the part of the body to which it is joined is called the thorax, and to this is added the posterior part or abdomen; this part is extremely various in form in different insects; in some it is round and full, in others long and extended. The antennæ arise from the head, and are generally composed of eleven pieces variously disposed; these wonderful organs are possessed of great sensibility, and they certainly serve to convey information to the insect, of the nature of one of the special senses; it was formerly thought to be simply that of touch very much refined, or of smell, but it is now generally considered to be that of hearing, or a modification of it. The forms of the antennæ are very various; fig. 845 represents that of the cockchafer (Melolontha vulgaris). The legs proceed from the thorax as do the wings, the abdomen giving rise to none of the extremities; the feet of insects are all pretty much upon the same model, some being more developed than others, they have a pair of hooks or claws for catching and clinging to rough surfaces, and a pair of cushions or pads, covered in some cases with suckers.

Fig. 844.—Spiracle.

Fig. 845.—Antenna of cockchafer (melolontha vulgaris).

The foot of the common house-fly is most beautifully fitted for its progression and support. We have often wondered how the fly manages to support itself back downwards on the ceiling, or walk up glass. We give a cut of the fly’s foot (fig. 846).

The eyes of insects are also marvellous. There are only two, but each one is composed of numerous cells (ocelli), and look like a honey-comb. (See illustration, fig. 847.)

Fig. 846.—Foot of fly, magnified.

Fig. 847.—Compound eye. 1. Perpendicular section; 2. Surface.

Insects swarm in innumerable companies, and no one who has not seen the locusts descending upon the earth can form more than a faint idea of the devastation they occasion in an incredibly short time. These, as well as thousands of other insects, exist in myriads, and we must content ourselves, on this occasion, by merely noting the different orders and their characteristics, after we have mentioned some of the attributes common to all.

The term “insect” means cut into or divided, and so the insecta are divided, as already mentioned, into three parts,—head, thorax, and abdomen,—the thorax being subdivided into three rings, pro-thorax, meso-thorax, and meta-thorax—beginning, middle, and end. All insects have six legs, and usually two or four wings, though some have no wings at all. The legs are united to the thorax, the antennæ and eyes to the head. The abdomen contains the important sexual organs, a sting or defensive weapon, and in females the egg chamber.

Insects breathe by tubes in the sides, and consume a great quantity of air. Their powers of flying and leaping are too familiar to need dwelling upon. The wings display beautiful colours like those observable in the soap-bubble, others are covered with scales or hairs. The mouths vary very much with the species, as the manner of obtaining food is by suction or gnawing. The blood of insects is pale and thin.

The various transformations which insects undergo are always a subject of interest for the young student. The ugly forms which develop in beautiful creations are more astonishing than the change of the “ugly duckling” into the graceful swan.

Fig. 848.—Larva.

Fig. 849.—Pupa.

Insects come to maturity only after undergoing successive changes from the egg to the perfect animal. The eggs (some of which are very beautiful) are first deposited in some safe place, either attached to a leaf or tied up in a small bundle by silken threads spun by the parent insect, and in some nutritious substance, so that when it comes to life it may at once have food; this is sometimes in manure, sometimes in flesh, and sometimes under the skin of a living animal (few are exempt from this infliction), where they remain for a time and then come forth as maggots, caterpillars, etc.; in this state they are called larvæ,—these are generally active creatures and eat most voraciously, which seems to be the principal act of this state of their existence. These larvæ frequently change their skins as they grow, and at last they assume the next stage of their life, the pupa or chrysalis state, which is one generally of complete inactivity; many of these larvæ weave themselves a covering of a sort of silk, to defend them while in the pupa state,—such as the silkworm, whose covering (cocoon) is the source of all the silk of commerce,—others merely place themselves in a situation of security. The pupa remains dormant for a certain time, and then becomes the imago or perfect insect (the last state of its existence), such as a moth, a butterfly, a beetle, etc. These are of different sexes, and in due time produce a batch of eggs and then die; these eggs are often incredible in numbers, amounting to many thousands—but few escape the watchful eyes of other insects and of birds who feed upon them.

But there are some of the insecta which do not undergo metamorphosis; the Aptera or wingless insects include these, as the flea and such parasites which bore into other animals, and deposit their eggs within them.

Fig. 850.—Imago.

Insects have very little means for making themselves audible, at least so far as can be ascertained. The humming of bees and flies and other insects are, of course, not intended to represent the voice. The cricket’s “chirp,” as people commonly imagine, but the sound is attributable to the rubbing together of the wings or wing-cases, as is the noise produced by the field-cricket. There is a very peculiar sound attributable to the “Death-Watch,” a ticking, and to nervous people terrible warning of dissolution. It may reassure some one, perhaps, to know that this “unearthly sound” is caused simply by the insect beating its head against a piece of wood to attract its mate, as the female glow-worm lights her lamp to guide her lord to her bower.

The Insecta may simply be divided into nine orders:—

1 Coleoptera.	Beetle tribe.	Case-winged.
2 Orthoptera.	Locusts, crickets, etc.	Straight-winged.
3 Neuroptera.	Dragon-flies, etc.	Nerve-winged.
4 Hymenoptera.	Bees, ants, wasps, etc.	Membrane-winged.
5 Strepsiptera.	Parasites of the foregoing.	Twisted-winged.
6 Lepidoptera.	Moths and butterflies.	Scale-winged.
7 Hemiptera.	Bugs, water-boatmen.	Half-winged.
8 Diptera.	House-fly, gnat.	Two-winged.
9 Apraniptera.	Fleas, “chigos.”	Wingless.
(Of these the metamorphoses of 1, 3, 4, 6, and 8 are complete).

Fig. 851.—The Stag-Beetle (Lucanus cervus).

The Coleoptera are well represented in England as beetles. They have four wings, but the outer pair serve as coverings to the inner ones. They are termed Elytra, and are horny in texture. These beetles are short-lived, but useful as scavengers, and serve to manure the ground by burying objectionable matter. The larvæ of beetles eat tremendously. The stag-beetle is a formidable-looking animal, and the lady-bird is well known as an enemy to the aphides on our rose trees. The tiger-beetle, cockchafer, and various water-beetles belong to this family. The scarabee, or sacred Egyptian beetle, also will be found classed with the coleoptera. Many of these beetles are excellent scavengers, and some called burying beetles remove the soil underneath the carcases of birds and other small dead animals, letting them fall down below the ground level; the beetles then lay their eggs in the body, so that sustenance may be at hand for the young when hatched.

The Orthoptera include our cockroaches, miscalled “black beetles,” the locusts, crickets, etc. The ravages of the locust are well known. The larvæ of the orthoptera has no wings, but otherwise is very like the grown insect. They change their skins frequently before they become perfect insects.

Passing the “nerve-winged” dragon-flies and caddis, whose larvæ case is so familiar and useful as bait, we come to the very important and interesting order of Hymenoptera, with four membranous wings. In this rank we find bees, wasps, and ants, the first and last named being proverbial for industry and examples of almost superhuman reasoning powers, and a similitude to man’s arrangements in labour and house-building marvellous to contemplate. A study of the habits of ants, bees, and wasps will reveal a state of society existing amongst them which more nearly resembles man in feelings and habits, for these insects possess means of oral communication.

Fig. 852.—Honey-lapping apparatus of wild sea-bee (Halictus), (a, magnified; a b, more highly magnified).

All these insects are armed with a sting, or other offensive weapon. The ant possesses the “formic” acid, which derives its name from the possessor. The destructive white ants will eat away a wooden house very quickly, sapping and mining it in all directions till it is a mere skeleton. The habits of bees are so well known and have been so often described that we need not detail them. The manner in which the ants “milk” the aphides is curious and interesting.

Fig. 853.—Scales from moth’s wing (magnified).

The Strepsiptera order includes very few species, so we may pass quickly to the Lepidoptera, the butterflies and moths, whose beautiful colourings and markings have attracted us all from childhood. There are about 12,000 species of the lepidoptera, and they are divided into “moths” and “butterflies,” the former being seen in twilight, or darkness, the latter in sunlight. They can readily be distinguished by the antennæ, those of the butterfly being tipped, or knobbed. The silkworm belongs to this family. These insects undergo complete metamorphosis. The remaining two orders of insects include the house-flies and gnats; and the flea, and jigger, or chigo, which penetrates the skin and lays its eggs in the flesh, causing thereby dangerous inflammation.

Crustacea.

Fig. 854.—Crustacea. 1. Lobster (Astacus marinus); 2. Cray-fish (Astacus fluviatilis); 3. Crab (Cancer pagurus); 4. Shrimp (Crangon vulgaris); 5. Prawn (Palæmon serratus).

This class includes a number of familiar animals such as the barnacle, the crab, the lobster, shrimp, etc.; and curious as it may appear are closely related to our spiders. Their cases or coverings are all articulated or disposed in distinct segments. They breathe through gills or by tubes, and possess legs, or appendages for walking, eating, or guidance. They are generally marine creatures.

The shell of the crustacea is composed largely of lime, and of course becomes very hard in time. It is formed from the skin. The body, like that of an insect, is composed of head, thorax, and abdomen, divided into twenty-one segments, of which seven occupy the head, seven the thorax, and the remainder the abdomen. Twenty segments are furnished with legs, or feelers, or claws—a pair to a segment. The lobster or crayfish will give excellent examples of the anatomy of the macrura or lobster kind of crustacea. The heart is situated in the back.

The following table given by Professor Nicholson will explain the “segments and appendages” of the lobster:—

	1st	Segment,	Eyes.
	2nd	“	Lesser antennæ
	3rd	“	Greater antennæ.
Head	4th	“	Pair of biting jaws.
	5th	“	First pair of chewing jaws.
	6th	“	Second pair of chewing jaws.
	7th	“	First pair of foot jaws.
	8th	“	Second pair of foot jaws.
	9th	“	Third pair of foot jaws.
	10th	“	First pair of legs (claws).
Thorax	11th	“	Second pair of legs (small claws).
	12th	“	Third pair of legs (small claws).
	13th	“	Fourth pair of legs.
	14th	“	Fifth pair of legs.
	15th	“	Ground appendages.
	16th	“	Swimmerets.
	17th	“	Swimmerets.
Abdomen	18th	“	Swimmerets.
	19th	“	Swimmerets.
	20th	“	Large swimmerets.
	21st	“	No appendages (tail fin).

The tail is, as may be supposed, the great aid to locomotion in the lobster family, and they can swim backwards with great rapidity by its assistance. Lobsters shed their claws when alarmed, and are easily caught by a glittering bait.

The hermit crabs are interesting creatures, but do not possess the horny coat of the crab or lobster. They are therefore compelled to inhabit an empty shell, into which they thrust themselves, holding to the bottom of it by their tail, while a large claw guards the entrance. When the animal gets too big for his house he moves to another, leaving the old home for another hermit of the shore.

The crabs have no developed tails, and are therefore called brachyura—“short-tailed,” and they are walking creatures. There are king crabs, land crabs, and the common swimming crab. These animals can shed their shells as other crustaceans, and a curious fact is they shed them whole. How the claws come out must remain more or less a mystery. Réaumur investigated the action of the crayfish, and noticed that as the casting time approached the crustacea retired to some hiding-place and remained without eating. The shell becomes gradually loosened, and at last by putting its feet against a stone and pushing backwards the animal jerks himself away. It must be a painful operation, for the mill-like teeth of the stomach are also rejected, and the joints do not give way. After a while a new shell appears, and is cast in due time as before.

The eyes of the crustacea are situated in front, and are composed like the insects, or are simple, like spiders. They possess a sense of hearing evidently. The eggs of the lobster are carried by the female, and they are termed the “coral” in consequence of their red and beadlike appearance. Our space will not admit of our saying much more concerning the interesting crustacea, though the barnacles, so well known by sight by all dwellers at the sea, and called Cirripedia, which fix themselves to rocks and ships, deserve notice. The young are capable of movement, and this fact was first discovered in 1830. It resembled a mussel, but when kept in sea-water it adhered to the vessel which retained it. The cirripedia are so called from the cirri or arms which they possess, and by which they are enabled to entangle or catch their food, as in a net. They hold themselves by a “foot stalk.” The goose-mussel, or barnacle, is very common, but must not be confounded with the limpet.

Dr. Baird gives the following description of them:—“The cirripeds are articulated animals contained within a hard covering composed of several pieces and consisting of calcified chitine. The body of the animal is enclosed in a sac lined with the most delicate membrane of chitine, which in one group is prolonged into a peduncle and contains the ova; the body is distinctly articulated and placed with the back downwards.

Arachnida—Spiders.

Fig. 855.—Arachnida. 1. Spider (Epeira diadema); 2. Scorpion (Scorpio).

There are many families of arachnida besides the well-known garden and house spiders. The sea spiders, though classed with the arachnida, are sometimes placed amongst the crustacea. We have the “tick” and the cheese-mite and the scorpions; all of which belong to the spider family. But the true spiders are known by the joining of the two upper segments, the thorax and head being united (cephalo-thorax). The pretty and marvellous webs are spun from abdominal glands through small apertures. The fluid hardens in its passage sufficiently to be woven into threads to resist the struggles of the captured prey. The forms of these webs vary, but some spiders do not catch their victims in the net; they pounce upon them cat fashion. The large house spider is well known to all. The garden spider is seen in the illustration (fig. 855) with the scorpion. The habits of spiders will be found a very interesting study, and many volumes have been devoted to them. The water spider is a frequent inmate of an aquarium, and the bubble of air he takes down with him to breathe serves as a means of living while he is seeking his aquatic prey.

We will close our rapid survey of the invertebrate animals with a glance at the Mollusca, which are divided into six classes (see [page 703]). The first is the Tunicata, which have no shell or hard covering, and come under the denomination of molluscoids, and belong to a lower order. The true mollusca include the Brachiopoda, which have a pair of shells. They are called “arm-footed” because a long cord or tendon passes through one of the shells, and fixes the mollusc to the rock. The Lingula of this class have been discovered in very old formations such as the Devonian period, and indeed appear to have been amongst the first created animals.

Fig. 856.—Mollusca. 1. Nautilus (Argonauta); 2. Clio Borealis; 3. Mussel (Mytilus edule).

The Lamellibranchiata include the oyster, cockle, mussel, etc. They are well known, and scarcely need description. The Pteropoda have no shell. The Gasteropoda are very numerous, and periwinkles, whelks, snails, etc., belong to this class. They progress by a muscular “mantle,” which is extended and contracted. The “horns” have eyes at the extremities. When they retire into their “houses” they can close the door by a kind of lid called the “operculum.”

The Cephalopods include the nautilus and the cuttle fish, the terrible squid, or octopus, etc. Wonderful tales are told of the tenacity and ferocity of the “Poulpes,” and no doubt in long-past ages these animals attained a gigantic growth. They are very unpleasant enemies, and the cold, slimy grasp of the long tentacles is apt to give one the “horrors,” while the terrible head and beak fill one with dismay. The poulpes are very formidable opponents, and discretion will certainly be the better part of valour when they appear in our vicinity.

We must here close our sketch of the Invertebrates, and we regret that the limits of our volume will not permit us to continue this interesting subject, nor can we find space, at present, for even the barest description of the Vertebrate animals.

The sun-fish (Orthagoriscus).

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CHAPTER LVI.
THE ANALYSIS OF CHANCE AND MATHEMATICAL GAMES.

MAGIC SQUARES—THE SIXTEEN PUZZLE—SOLITAIRE—EQUIVALENTS.

We will now proceed to draw our readers’ attention to several experiments very famous at a former period, but which our own generation has completely overlooked. We refer to the Analysis of Chance, a science still known under the title of Calculation of Probabilities, formerly cultivated with so much ardour, but to-day almost fallen into oblivion.

Originating in the caprice of the clever Chevalier de Méré, who in 1654 suggested the game to Pascal, the analysis of chance has given rise to investigations of an entirely novel kind, and attempts have been made to measure the mathematical degree of credence to be given to simple conjectures. We will first recapitulate the principles laid down by Laplace on this subject. We know that of a certain number of events, one only can happen, but nothing leads us to the belief that one will happen more than the other. The theory of chance consists in reducing all the events of the same kind to a certain number of equally possible cases, such, that is to say, that we are equally undecided about, and to determine the number of cases favourable to the event, whose probability we are seeking. The ratio of this number to that of all possible cases is the measure of this probability, which is thus a fraction, the numerator of which is the number of favourable cases, and the denominator the number of all possible cases. When all the cases are favourable to an event, its probability changes to certainty, and it is then expressed by the unit. Probabilities increase or diminish by their mutual combination; if the events are independent of each other, the probability of the existence of their whole is the product of their particular probabilities. Thus the probability of throwing an ace with one dice being 1/6, that of throwing two aces with two dice is 1/36. Each of the sides of one dice combining with the six sides of the other, there are thirty-six possible cases, among which one only gives the two aces. When two events depend on each other, the probability of the double event is the product of the probability of the first event by the probability that, that event having occurred, the other will occur. This rule helps us to study the influence of past events on the probability of future events. If we calculate á priori the probability of the event that has occurred and an event composed of this and another expected event, the second probability divided by the first, will be the probability of the expected event, inferred from the observed event.

The probability of events serves to determine the hope or fear of persons interested in their existence. The word hope here expresses the advantage which someone expects in suppositions which are only probable. This advantage in the theory of chances is the product of the hoped-for sum by the probability of obtaining it; it is the partial sum which should arise when one does not wish to run the risks of the event, supposing that the apportionment corresponds to the probabilities. This apportionment is only equitable when we abstract from it all foreign circumstances; because an equal degree of probability gives an equal title to the hoped-for sum. This advantage is called mathematical hope. Nevertheless, the rigorous application of this principle may lead to an inadmissible consequence. Let us see what Laplace says. Paul plays at heads and tails, on the understanding that he receives two shillings if he succeeds at the first throw, four shillings if he succeeds at the second, eight at the third, and so on. His stake on the game, according to calculation, must be equal to the number of throws; so that if the game continues indefinitely, the stake also continues indefinitely. Yet, no reasonable man would venture on this game even a moderate sum, £2 for example. Whence, therefore, comes this difference between the result of the calculation, and the indication of common-sense? We soon perceive that it proceeds from the fact, that the moral advantage which a benefit procures for us is not proportional to this advantage, and that it depends on a thousand circumstances, often very difficult to define, but the chief and most important of which is chance. In fact, it is evident that a shilling has much greater value for one who has but a hundred than for a millionaire. We must, therefore, distinguish in the hoped-for good between its absolute and its relative value; the latter regulates itself according to the motives which cause it to be desired, while the former is independent. In the absence of a general principle to appreciate this relative value, we give a suggestion of Daniel Bernouilli which has been generally admitted.

The relative value of an extremely small sum is equal to its absolute value, divided by the total advantage of the interested person. On applying the calculus to this principle, it will be found that the moral hope, the growth of chance due to expectations, coincides with the mathematical hope, when chance, considered as a unit, becomes infinite in proportion to the variations it receives from expectations. But when these variations are a sensible portion of the unit, the two hopes may differ very greatly from each other. In the example cited, this rule leads to results conformable to the indications of common-sense. We find, in point of fact, that if Paul’s fortune amounts only to £8, he cannot reasonably stake more than 7s. on the game. At the most equal game, the loss is always, relatively greater than the gain. Supposing, for example, that a person possessing a sum of £4, stakes £2 on a game of heads or tails, his money after placing his stake will be morally reduced to £3 11s. 0d.—that is to say, this latter sum will procure him the same moral advantage as the condition of his funds after his stake. Whence we draw this conclusion: that the game is disadvantageous, even in the cases where the stake is equal to the product of the sum hoped for by the probability. We may, therefore, form an idea of the immorality of games in which the hoped-for sum is below this product.

Fig. 857.—The game of the needle.

Jacques Bernouilli has thus laid down the result of his investigations on the calculation of probabilities. An urn containing white and black balls is placed in front of the spectator, who draws out a ball, ascertaining its colour, and puts it back in the urn. After a sufficient number of draws, the total number of extracted balls divided by the total number of balls represents a fraction very near to that which has for a numerator the real number of white balls existing in the urn, and for the denominator the total number of balls. In other words, the ratios of the number either of extracted white balls, or the whole of the white balls to the total number, tend to become equal; that is, the probability derived from this experiment approaches indefinitely towards a certainty. The two fractions may differ from each other as little as possible, if we increase the number of draws. From this theorem we deduce several consequences.

1. The relations of natural effects are nearly constant when these effects are considered in a great number.

2. In a series of events indefinitely prolonged, the action of regular and constant causes affects that of irregular causes.

Applications.—The combinations presented by these games have been the subject of former researches regarding probabilities. We will complete our exposition with two more examples.

Two persons, A and B, of equal skill, play together on the understanding that whichever beats the other a certain number of times, shall be considered to have won the game, and shall carry off the stakes. After several throws the players agree to give up without finishing the game; and the point then to be settled, is in what manner the money is to be divided between them. This was one of the problems laid before Pascal by the Chevalier de Méré. The shares of the two players should be proportional to their respective probabilities of winning the game. These probabilities depend on the number of points which each player requires to reach the given number. A’s probabilities are determined by starting with the smallest numbers, and observing that the probability equals the unit, when player A does not lose a point. Thus, supposing A loses but one point, his chance is 1·2, 3·4, 7·8, etc., according as B misses one, two, or three points. Supposing A has missed two points, it will be found that his chance is as 1·4, 1·2, 11·6, etc., according as B has missed one, two, or three points, etc. Or we may suppose that A misses three points, and so on.

We should note, en passant, that this solution has been modified by Daniel Bernouilli, by the consideration of the respective fortune of the players, from which he deduces the idea of moral hope. This solution, famous in the history of science, bears the name of the Petersburgh problem, because it was made known for the first time in the “Memoires de l’Académie de Russie.”

We will now describe the game of the needle. It is a genuine mathematical amusement, and its results, indicated by theory, are certainly calculated to excite astonishment. The game of the needle is an application of the different principles we have laid down.

ig. 858.—The needle game.

Fig. 859.—The needle game.

If we trace on a sheet of paper a series of parallel and equi-distant lines, AA1, BB1, CC1, DD1, and throw down on the paper at hazard a perfectly cylindrical needle, a b, the length of which equals half the distance between the parallel lines (figs. 858 and 859), we shall discover this curious result. If we throw down the needle a hundred times, it will come in contact with one of the parallel lines a certain number of times. Dividing the number of attempts with the number of successful throws, we obtain as a quotient a number which approaches nearer the value of the ratio between the circumference and the diameter in proportion as we multiply the number of attempts. This ratio, according to the rules of geometry, is a fixed number, the numerical value of which is 3·1415926. After a hundred throws we generally find the exact value up to the two first figures: 3·1. How can this unexpected result be explained? The application of the calculus of probabilities gives the reason of it. The ratio between the successful throws and the number of attempts, is the probability of this successful throw. The calculation endeavours to estimate this probability by enumerating the possible cases and the favourable events. The enumeration of possible cases exacts the application of the principle of compound probabilities. It will be easily seen that it suffices to consider the chances of the needle falling between two parallel lines, AA1 and BB1 (fig. 858), and then to consider what occurs in the interval, m n, equal to the equi-distance. To obtain a successful throw, it is necessary then:—

1. That the middle of the needle should fall between m and l, the centre of m o. 2. That the angle of the needle with m o will be smaller than the angle, m c b. The calculation of all these probabilities and their combination by multiplication, according to the rules of compound probabilities, gives as the final expression of probability the number.

This curious example justifies the theorem of Bernouilli relating to the multiplication of events; there is no limit to the approximation of the result, when the attempts are sufficiently prolonged. When the length of the needle is not exactly half the distance between the parallel lines, the practical rule of the game is as follows: The ratio between the number of throws and the number of successful attempts must be multiplied by double the ratio between the length of the needle and the distance between the parallel lines. In the case cited above, the double of the latter ratio equals the unit. We will give an application to this. A needle two inches long is thrown 10,000 times on a series of parallel lines, two-and-a-half inches apart; the number of successful throws has been found to equal 5000. We take the ratio 1090/5009, and multiply it by the ratio 1000/636 and the product is 3·1421. The true value is 3·1415. We have an approximation of 6/10000.

The dimensions indicated in this experiment are those which present in a given number of attempts the most chances of obtaining the greatest possible approximation. We will conclude these remarks on games by some observations borrowed from Laplace.

The mind has its illusions like the sense of sight; and just as the sense of touch corrects the latter, reflection and calculation correct the former. The probability founded on an every-day experience, or exaggerated by fear or hope, strikes us as a superior probability, but is only a simple result of calculation.

In a long series of events of the same kind, the mere chances of accident sometimes offer these curious veins of good or bad fortune, which many persons do not hesitate to attribute to a kind of fatality. It often happens in games which depend both on chance and the cleverness of the players, that he who loses, overwhelmed with his want of success, seeks to repair the evil by rash playing, which he would avoid on another occasion; he thus aggravates his own misfortune and prolongs it. It is then, however, that prudence becomes necessary, and that it is desirable to remember that the moral disadvantage attaching to unfavourable chances is increased also by the misfortune itself.[41] Mathematical games, formerly so much studied, have recently obtained a new addition in the form of an interesting game, known as the “Boss” puzzle. It has been introduced from America, and consists of a square box, in which are placed sixteen small wooden dice, each bearing a number (fig. 860). No. 16 is taken away, and the others are placed haphazard in the box, as shown in fig. 861. The point is then to move the dice, one by one, into different positions, so that they are at last arranged in their natural order, from one to fifteen; and this must be accomplished by slipping them from square to square without lifting them from the box. If the sixteenth dice is added, the game may be varied, and we may seek another solution of the problem, by arranging the numbers so that the sum of the horizontal, vertical, and diagonal lines gives the number 34. In this form the puzzle is one of the oldest known. It dates from the time of the primitive Egyptians, and has often been investigated during the last few centuries, belonging, as it does, to the category of famous magic squares, the principles of which we will describe. The following is the definition given by Ozanam, of the Academy of Sciences, at Paris, at the end of the seventeenth century. The term magic square is given to a square divided by several small equal or broken squares, containing terms of progression which are placed in such a manner that all those of one row, either across, from top to bottom, or diagonally, make one and the same sum when they are added, or give the same product when multiplied. It is therefore evident from this definition, that there are two kinds of magic squares, some formed by terms of arithmetical progression, others by terms of geometrical progression. We must also distinguish the equal from the unequal magic squares.

Fig. 860.—The sixteen puzzle.

Fig. 861.—The numbers placed at hazard, and No. 16 removed.

We give here several examples of magic squares with terms of mathematical progression, among them the square of 34, giving one of the solutions to the puzzle just described (fig. 862). We also give an example of a magic square composed of terms of geometrical progression. The double progression for examples 1, 2, 4, 8, 16, 32, 64, 128, 256, as here arranged (fig. 863), forms such a square that the product obtained by multiplying the three terms of one row, or one diagonal, is 4,096, which is the cube of the mean term 16. The squares have been termed magic, because, according to Ozanam, they were held in great veneration by the Pythagoreans. In the time of alchemy and astrology, certain magic squares were dedicated to the seven planets, and engraved on a metal blade which sympathized with the planet. To give an idea of the combinations to which the study of magic squares lends itself, it is sufficient to add that mathematicians have written whole treatises on the subject. Frénicle de Bessy, one of the most eminent calculators of the seventeenth century, consecrated a part of his life to the study of magic squares. He discovered new rules, and found out the means of varying them in a multitude of ways. Thus for the magic square, the root of which is 4, only sixteen different arrangements were known.

Fig. 862.—Examples of magic squares formed by terms of arithmetical progression.

Frénicle de Bessy found 880 new solutions. An important work from the pen of this learned mathematician has been published under the title of “Carrés ou Tables Magiques,” in the “Memoirs de l’Académie Royale des Sciences,” from 1666-1699, vol. v. Amateurs, therefore, who are accused of occupying themselves with a useless game, unworthy the attention of serious minds, will do well to bear in mind the works of Frénicle, and better still, to consult them.

Fig. 863.—Magic square formed by terms of geometrical progression.

We have so far considered only the first part of the puzzle. We may now examine the problem to which specially it has given rise. We are quite in accord with M. Piarron de Mondesir, who has been so good as to enlighten us upon the subject, which is really much more difficult than it appears.

A French paper once proposed to give a prize of 500 francs to any individual who would solve the following problem:—

Throw the numbers out of the box, replace them at hazard, then in arranging them place them in the following order (A fig. 864).

Fig. 864.—The Sixteen Puzzle.

Now nobody solved this problem, because in nine cases out of ten it is impossible to do so. The first twelve numbers will come correctly into their places, and even 13 can be put in its place without much trouble; but, instead of getting the last row right we shall find it will come out like B, viz., 14, 15, 13, in the large majority of instances. So any case can be solved in one of the two results given above, and we can tell in advance, without displacing a number, in which way the puzzle will eventuate.

Fig. 865.—Example 1.

Fig. 866.—Example 2.

Let us give this problem our attention for a few minutes, and we shall not find it difficult.

Take the first example. We will throw the cubes out of the box and put them back in the order shown in fig. 865.

We see now that 1 occupies the place of 11, 11 that of 7, 7 that of 8, 8 that of 6, 6 of 15, 15 of 1. This much is evident without any study. We formulate these figures as follows, beginning with 1 and working from figure to figure till we are led to 1 again, and so on.

1st. Series.—1, 11, 7, 8, 6, 15, 1 (6) even.

Counting the number of different cubes we have 6; and we put (6) in a parenthesis. We call the first series even because 6 is an even number.

We now establish, by the same formula, a second series commencing with 2, and going back to it, thus—

2nd Series.—2, 4, 2	(2) even.
3rd Series.—3, 5, 10, 12, 3	(4) even.
4th Series.—9, 13, 14, 9	(3) uneven.

We have now four series, the total number of points equal 15, as there ought to be, for one cube is absent.

Let us now take another example (see fig. 866), and by working as before we have four series again, viz:—

1st Series.—1, 7, 1	(2) even.
2nd Series.—2, 11, 3, 8, 4, 15, 2	(6) even.
3rd Series.—5, 12, 13, 5	(3) uneven.
4th Series.—9, 14, 10, 9	(3) uneven.

This gives us only 14 as a total, because 6 has not been touched at all.

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And now for the rule, so that we may be able to ascertain in advance, when we have established our series, whether we shall find our puzzle right or wrong at the end. We must put aside all unplaced numbers and take no notice of uneven series. Only the even series must be regarded.

Thus if we do not find 1, or if we find 2, 4, or 6, the problem will come into A as a result. If we find 1, 3, 5, or 7, the case will eventuate as in B (fig. 864). Let us apply the rule to the problems we have worked, and then the reason will be apparent.

In the first we find three even series; the problem will then end as in B diagram (fig. 864), for the number of like series is odd.

In the second we find two even series (pairs); we shall find our problem work out as in diagram A (fig. 864), for the number of like series is even, one pair in each.

We are now in possession of a simple rule, both rapid and infallible, and which will save considerable trouble, as we can always tell beforehand how our puzzle will come out. Any one can test the practicability of the rules for himself, but we may warn the reader that he will never be able to verify every possible instance, for the possible cases are represented by the following sum—

2×3×4×5×6×7×8×9×10×11×12×13×14×15.

That is to say, 1,307,674,368,000 in all.

Solitaire.

This somewhat ancient amusement is well known, and the apparatus consists of a board with holes to receive pegs or cups to receive the balls, as in the illustrations (figs. 867 and 870.) The usual solitaire board contains thirty-seven pegs or balls, but thirty-three can also be played very well. Many scientific people have made quite a study of the game, and have published papers on the subject. M. Piarron de Mondesir has given two rules which will prove interesting.

The first is called that of equivalents, and supposes the game to be played out to a conclusion; the second, called the ring-game, admits of a calculation being made so that the prospects of success can be gauged beforehand.

The method of play is familiar, so we need not detail it. It is simply “taking” the balls by passing over them in a straight line. The method of “equivalents” consists in replacing one ball with two others, as we will proceed to explain by the diagram (fig. 868).

Fig. 867.—Solitaire.

Suppose we try the 33 game, which consists in filling every hole with the exception of the centre one, and in “taking” all the balls, leaving one solitary in the centre at the last. Suppose an inexperienced player arrives at an impossible solution of five balls in 4, 11, 15, 28, and 30.

To render the problem soluble, and to win his game, I will replace No. 11 by two equivalents, 9 and 10, the ball 28 by two others, 23 and 16, and the ball 30 by 25 and 18. These substitutions will not change the “taking off,” for I can take 10 with 9, 23 with 16, and 25 with 18. But by so doing I substitute for an irreducible solution of five balls a new system of eight (those shown with the line drawn through them in the diagram), which can easily be reduced to the desired conclusion, and the game will be achieved.

There are in reality three terminations possible to the problem—the single ball, the couple, and the tierce; that is, you may have only one left, or two placed diagonally, such as 9-17, 25-29, or a system of three in a straight line, 9-16-23. By the “equivalents” you can always succeed in solving the problem desired.

We will now point out four transformations which are very easy to effect, and result from the rule of “equivalents.”

1. Replacement of the two balls, situated on the same line and separated by an empty cup, by one put into that cup. Thus I can replace 23 and 25 by a single ball at 24.

2. Suppression of tierces. And by the above movement I suppress the tierce 9-16-23.

3. Correspondent “cases” are two holes situated in the same line and separated by two cups. If two corresponding cups are filled, I can suppress the balls which occupy them. So I can put aside 4 and 23.

Fig. 868.—Correspondents and equivalents.

4. It is permissible to move a ball into one of the correspondent cups if it be vacant; thus I can put 10 into 29.

These are the four transformations which can be made evident with the rings, without displacing the balls. To do this we need have only seven rings large enough to pass over the balls and to surround the holes in which they rest. Let us take an example.

Solitaire with 33 holes (fig. 869). Final solution of the single ball.

1st Vertical row: 7 and 21 are occupied, and the intermediate hole 14, being empty, I place a ring upon 14.

2nd Vertical row: No. 8 takes 15, and comes into 22; I place a ring on 22.

3rd Vertical row: I suppress the corresponding balls, 4-23 and 16-31, there now only remains 9, so I place a ring on 9.

4th Vertical row: I suppress the correspondents 10-29, put 2 into 17, and I place a ring upon 17.

5th Vertical row: I suppress correspondents 6-25, put 33 into 18, and I place a ring upon 18.

6th Vertical row: No. 12 takes 19 and comes to 26; I place a ring on 26.

7th Vertical row: No. 20 is the only ball; I place a ring on 20.

(It must be understood that these operations should be proceeded with mentally; the balls must not be disturbed.)

We have thus reduced the problem to seven ringed balls, which are 14, 22, 9, 17, 18, 26, and 20 which are indicated on the diagram by the line drawn through each vertically. They are all comprised in the three horizontal rows, 3, 4, 5.

Fig. 869.—Single ball solution.

We can now set to work upon these three rows in the same manner as before, considering the rings as balls.

3rd row: We find (and leave) a ring upon 9.

4th row: The two corresponding rings, 17-20, neutralize each other, and we suppress them. We carry 14 to 17, and take 17 with 18, which comes into 16. We leave a ring on 16.

5th row: Carry the ring 26 to 23, take 23 with 22, which comes thus to 24, and we leave a ring on 24.

We now have reduced our problem to three rings, 9, 16, and 24, all in the central square, indicated in the diagram by horizontal bars. It is easy to see that 9 will take 16 and 24 and come into 25, and 25 will remain alone—as was intended to be done—a single ball upon the board, indicated by the circle around it in the cut.

By playing the “equivalent” method you will always arrive at this result—a single ball in No. 25. It may now be perceived how we cannot only arrive at a satisfactory solution, but by means of the rings ascertain whether we shall succeed in our game without disturbing a single ball. After some experience we may even learn to dispense with the rings altogether.

Fig. 870.—Solitaire board.

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