TRANSCRIBER'S NOTES

Obvious typographical and punctuation errors have been corrected after careful comparison with other occurrences within the text and consultation of external sources.

More detail can be found at the end of the book.

A PRIMITIVE USE OF THE ANIMAL MACHINE THAT IS STILL IN VOGUE IN MANY EUROPEAN COUNTRIES.

(From the painting by J. Didier, in the Musée du Luxembourg, Paris.)

[EVERY-DAY SCIENCE]

BY

HENRY SMITH WILLIAMS, M.D., L.L.D.

ASSISTED BY

EDWARD H. WILLIAMS, M.D.

VOLUME VI

THE CONQUEST OF NATURE

ILLUSTRATED

NEW YORK AND LONDON

THE GOODHUE COMPANY

PUBLISHERS MDCCCCIX

Copyright, 1910, by The Goodhue Co.

All rights reserved

[CONTENTS]

CHAPTER I

MAN AND NATURE

The Conquest of Nature, p. 4—Man's use of Nature's gifts, p. 6—Man the "tool-making animal," p. 7—Science and Civilization, p. 8—Clothing and artificially heated dwellings of primitive man, p. 10—Early domestication of animals, p. 11—Early development to the time of gunpowder, p. 12—The coming of steam and electricity, p. 15—Mechanical aids to the agriculturist, p. 19—The development of scientific agriculture, p. 20—Difficulties of the early manufacturer, p. 21—The development of modern manufacturing, p. 24—The relation of work to human development, p. 25—The decline of drudgery and the new era of labor-saving devices, p. 27.

CHAPTER II

HOW WORK IS DONE

Primitive man's use of the lever, p. 29—The use of the lever as conceived by Archimedes, p. 21—Wheels and pulleys, p. 32—Other means of transmitting power, p. 35—Inclined planes and derricks, p. 37—The steam-scoop, p. 38—Friction, p. 39—Available sources of energy, p. 41.

CHAPTER III

THE ANIMAL MACHINE

The oldest machine in existence, p. 43—The relation of muscle to machinery, p. 44—How muscular energy is applied, p. 44—The two types of muscles, p. 45—How the nerve-telegraph controls the muscles, p. 47—The nature of muscular action, p. 49—Applications of muscular energy, p. 52—The development of the knife and saw, p. 53—The wheel and axle, p. 55—Modified levers, p. 57—Domesticated animals, p. 59—Early application of horse-power, p. 60—The horse-power as the standard of the world's work, p. 61.

CHAPTER IV

THE WORK OF AIR AND WATER

First use of sails for propelling boats, p. 62—The fire engine of Ctesibius, p. 63—Suction and pressure as studied by the ancients, p. 64—Studies of air pressure, p. 65—The striking demonstration of Von Guericke, p. 66—The sailing chariot of Servinus, 1600 a.d., p. 68—The development of the windmill, p. 69—The development of the water-wheel, p. 70—The invention of the turbine, p. 72—Different types of turbines, p. 73—Hydraulic power and its uses, p. 74—The hydraulic elevator, p. 76—Recent water motors, p. 77.

CHAPTER V

CAPTIVE MOLECULES: THE STORY OF THE STEAM ENGINE

The development of the steam engine, p. 79—The manner in which energy is generated by steam, p. 80—Action of cylinder and piston, p. 81—Early attempts to utilize steam, p. 82—Beginnings of modern discovery, p. 83—The "engine" of the Marquis of Worcester, p. 84—Thomas Savery's steam pump, p. 85—Denis Papin invents the piston engine, p. 88—Newcomen's improved engine, p. 89—The use of these engines in collieries, p. 90—The wastefulness of such engines, p. 92—The coming of James Watt, p. 93—Early experiments of Watt, p. 95—The final success of Watt's experiments, p. 97—Some of his early engines, p. 98—Rotary motion, p. 99—Watt's engine, "Old Bess," p. 101—Final improvements and missed opportunities, p. 102—The personality of James Watt, p. 107.

CHAPTER VI

THE MASTER WORKER

Improvements on Watt's engines, p. 110—Engines dispensing with the walking beam, p. 111—The development of high-pressure engines, p. 112—Advantages of the high-pressure engine, p. 114—How steam acts in the high-pressure engine, p. 116—Compound engines, p. 117—Rotary engines, p. 119—Turbine engines, p. 124—The Turbinia and other turbine boats, p. 125—The action of steam in the turbine engine, p. 126—Advantages of the turbine engine, p. 127.

CHAPTER VII

GAS AND OIL ENGINES

Some early gas engines, p. 133—Dr. Stirling's hot-air engine, p. 133—Ericsson's hot-air engines, p. 134—The first practical gas engine, p. 135—The Otto gas engine, p. 136—Otto's improvement by means of compressed gas, p. 138—The "Otto cycle," p. 139—Adaptation of gas engines to automobiles, p. 140—Rapid increase in the use of gas engines, p. 141—Defects of the older hot-air engines, p. 145—Recent improvements and possibilities in the use of hot-air engines, p. 146.

CHAPTER VIII

THE SMALLEST WORKERS

The relative size of atoms and electrons, p. 148—What is electricity? p. 149—Franklin's one-fluid theory, p. 150—Modern views, p. 153—Cathode rays and the X-ray, p. 156—How electricity is developed, p. 159—The work of the dynamical current, p. 162—Theories of electrical action, p. 165—Practical uses of electricity, p. 168.

CHAPTER IX

MAN'S NEWEST CO-LABORER: THE DYNAMO

The mechanism of the dynamo, p. 173—The origin of the dynamo, p. 176—The work of Ampère, Henry, and Faraday, p. 177—Perfecting the dynamo, p. 178—A mysterious mechanism, p. 180—Curious relation between magnetism and electricity as exemplified in the dynamo, p. 182.

CHAPTER X

NIAGARA IN HARNESS

The volume of water at the falls, p. 184—The point at which the falls are "harnessed," p. 185—Within the power-house, p. 186—Penstocks and turbines, p. 188—A miraculous transformation of energy, p. 189—Subterranean tail-races, p. 191—The effect on the falls, p. 192—The transmission of power, p. 194—"Step-up" and "step-down" transformers, p. 198.

CHAPTER XI

THE BANISHMENT OF NIGHT

Primitive torch and open lamp, p. 202—Tallow candle and perfected lamp, p. 205—Gas lighting, p. 207—The incandescent gas mantle, p. 208—Early gas mantles, p. 209—How the incandescent gas mantle is made, p. 211—The introduction of acetylene gas, p. 212—Chemistry of acetylene gas, p. 214—Practical gas-making, p. 215—The triumph of electricity, p. 218—Davy and the first electric light, p. 220—Helpful discoveries in electricity, p. 222—The Jablochkoff candle, p. 223—Defects of the Jablochkoff candle, p. 225—The improved arc light, p. 226—Edison and the incandescent lamp, p. 228—Difficulties encountered in finding the proper material for a practical filament, p. 230—"Parchmentized thread" filament, p. 233—The tungsten lamp, p. 234—The mercury-vapor light of Peter Cooper Hewitt, p. 236—Advantages and peculiarities of this light, p. 240.

CHAPTER XII

THE MINERAL DEPTHS

Early mining methods, p. 242—Prospecting and locating mines, p. 243—"Booming," p. 246—Conditions to be considered in mining, p. 248—Dangerous gases in mines, p. 249—Artificial lights and lighting, p. 251—Ventilation and drainage, p. 252—Electric machinery in mining, p. 253—Electric drills, p. 254—Traction in mining, p. 256—Various types of electric motors, p. 257—"Telphers," p. 261—Electric mining pumps, p. 263—Some remarkable demonstrations of durability of electric pumps, p. 265—Electricity in coal mining, p. 266—Electric lighting in mines, p. 269.

CHAPTER XIII

THE AGE OF STEEL

Rapid growth of the iron industry in recent years, p. 271—The Lake Superior mines, p. 272—Methods of mining, p. 273—"Open-pit" mining, p. 274—Mining with the steam shovel, p. 276—From mine to furnace, p. 278—Methods of transportation, p. 279—Vessels of special construction, p. 281—The conversion of iron ore into iron and steel, p. 283—Blast furnaces, p. 284—Poisonous gases and their effect upon the workmen, p. 286—From pig iron to steel, p. 287—Modern methods of producing pig iron, p. 288—The Bessemer converter, p. 289—Sir Henry Bessemer, p. 291—The "Bessemer-Mushet" process, p. 293—Open-hearth method, p. 294—Alloy steels, p. 295.

CHAPTER XIV

SOME RECENT TRIUMPHS OF APPLIED SCIENCE

The province of electro-chemistry, p. 298—Linking the laboratory with the workshop, p. 299—Soda manufactories at Niagara Falls, p. 300—Producing aluminum by the electrolytic process, p. 300—Old and new methods compared, p. 301—Nitrogen from the air, p. 303—What this discovery means to the food industries of the world, p. 304—Prof. Birkeland's method, p. 307—Another method of nitrogen fixation, p. 309—Cost of production, p. 312—Electrical energy, p. 313—Production of high temperatures with the electric arc, p. 314—The production of artificial diamonds by the explosion of cordite, p. 315—Industrial problems of to-day and to-morrow, p. 316.

[ILLUSTRATIONS]

[THE CONQUEST OF NATURE]

In the earlier volumes we have been concerned with the growth of knowledge. For the most part the scientific delvers whose efforts have held our attention have been tacitly unmindful, or even explicitly contemptuous, of the influence upon practical life of the phenomena to the investigation of which they have devoted their lives. They were and are obviously seekers of truth for the mere love of truth.

But the phenomena of nature are not dissociated in fact, however much we may attempt to localize and classify them. And so it chances that even the most visionary devotee of abstract science is forever being carried into fields of investigation trenching closely upon the practicalities of every-day life. A Black investigating the laws of heat is preparing the way explicitly, however unconsciously, for a Watt with his perfected mechanism of the steam engine.

Similarly a Davy working at the Royal Institution with his newly invented batteries, and intent on the discovery of new elements and the elucidation of new principles, is the direct forerunner of Jablochkoff, Brush, and Edison with their commercial revolution in the production of artificial light.

Again Oersted and Faraday, earnestly seeking out the fundamental facts as to the relations of electricity and magnetism, invent mechanisms which, though they seem but laboratory toys, are the direct forerunners of the modern dynamos that take so large a share in the world's work.

In a word, all along the line there is the closest association between what are commonly called the theoretical sciences and what with only partial propriety are termed the applied sciences. The linkage of one with the other must never be forgotten by anyone who would truly apprehend the status of those practical sciences which have revolutionized the civilization of the nineteenth and twentieth centuries in its most manifest aspects.

Nevertheless there is, to casual inspection, a somewhat radical distinction between theoretical and practical aspects of science—just as there are obvious differences between two sides of a shield. And as the theoretical aspects of science have largely claimed our attention hitherto, so its practical aspects will be explicitly put forward in the pages that follow. In the present volume we are concerned with those primitive applications of force through which man early learned to add to his working efficiency, and with the elaborate mechanisms—turbine wheels, steam engines, dynamos—through which he has been enabled to multiply his powers until it is scarcely exaggeration to say that he has made all Nature subservient to his will. It is this view which justifies the title of the volume, which might with equal propriety have been termed the Story of the World's Work.

THE CONQUEST OF NATURE

[I]

MAN AND NATURE

"Young men," said a wise physician in addressing a class of graduates in medicine, "you are about to enter the battle of life. Note that I say the 'battle' of life. Not a playground, but a battlefield is before you. It is a hard contest—a battle royal. Make no mistake as to that. Your studies here have furnished your equipment; now you must go forth each to fight for himself."

The same words might be said to every neophyte in whatever walk of life. The pursuit of every trade, every profession is a battle—a struggle for existence and for supremacy. Partly it is a battle against fellow men; partly against the contending powers of Nature. The physician meets rivalry from his brothers; but his chief battle is with disease. In the creative and manufacturing fields which will chiefly concern us in the following volumes, it is the powers of Nature that furnish an ever-present antagonism.

No stone can be lifted above another, to make the crudest wall or dwelling, but Nature—represented by her power of gravitation—strives at once to pull it down again. No structure is completed before the elements are at work defacing it, preparing its slow but certain ruin. Summer heat and winter cold expand and contract materials of every kind; rain and wind wear and warp and twist; the oxygen of the air gnaws into stone and iron alike;—in a word, all the elements are at work undoing what man has accomplished.

THE STRUGGLE FOR EXISTENCE

In the field of the agriculturist it is the same story. The earth which brings forth its crop of unwholesome weeds so bountifully, resists man's approaches when he strives to bring it under cultivation. Only by the most careful attention can useful grains be made to grow where the wildlings swarmed in profusion. Not only do wind and rain, blighting heat and withering cold menace the crops; but weeds invade the fields, the germs of fungoid pests lurk everywhere; and myriad insects attack orchard and meadow and grain field in devastating legions.

Similarly the beasts which were so rugged and resistant while in the wild state, become tender and susceptible to disease when made useful by domestication. Aforetime they roamed at large, braving every temperature and thriving in all weathers. But now they must be housed and cared for so tenderly that they become, as Thoreau said, the keepers of men, rather than kept by men, so much more independent are they than their alleged owners. Tender of constitution, domesticated beasts must be housed, to protect them from the blasts in which of yore their forebears revelled; and man must slave day in and day out to prepare food to meet the requirements of their pampered appetites.

He must struggle, too, to protect them from disease, and must care for them in time of illness as sedulously as he cares for his own kith and kin. Truly the ox is keeper of the man, and the seeming conquest that man has wrought has cost him dear.

But of course the story has another side. After all, Nature is not so malevolent as at first glance she seems. She has opposed man at every stage of his attempted progress; yet at the same time she has supplied him all his weapons for waging war upon her. Her great power of gravitation opposes every effort he makes; yet without that same power he could do nothing—he could not walk or stay upon the earth even; and no structure that he builds would hold in place for an instant.

So, too, the wind that smites him and tears at his handiwork, may be made to serve the purposes of turning his windmills and supplying him with power.

The water will serve a like purpose in turning his mills; and, changed to steam with the aid of Nature's store of coal, will make his steam engines and dynamos possible. Even the lightning he will harness and make subject to his will in the telegraphic currents and dynamos.

And in the fields, the grains which man struggles so arduously to produce are after all no thing of his creating. They are only adopted products of Nature, which he has striven to make serve his purpose by growing them under artificial conditions. So, too, the domesticated beasts are creatures that belong in the wilds and in distant lands. Man has brought them, in defiance of Nature, to uncongenial climes, and made them serve as workers and as food-suppliers where Nature alone could not support them. Turn loose the cow and the horse to forage for themselves here in the inhospitable north, and they would starve. They survive because man helps them to combat the adverse conditions imposed by Nature, yet no one of them could live for an hour were not the vital capacities supplied by Nature still in control.

Everywhere, then, it is the opposing of Nature, up to certain limits, with the aid of Nature's own tools, that constitutes man's work in the world. Just in proportion as he bends the elements to meet his needs, transforms the plants and animals, defies and exceeds the limitations of primeval Nature—just in proportion as he conquers Nature, in a word, is he civilized.

Barbaric man is called a child of Nature with full reason. He must accept what Nature offers. But civilized man is the child grown to adult stature, and able in a manner to control, to dominate—if you please to conquer—the parent.

If we were to seek the means by which developing man has gradually achieved this conquest, we should find it in the single word, Tools; that is to say, machines for utilizing the powers of Nature, and, as it were, multiplying them for man's benefit. So unique is the capacity that man exerts in this direction, that he has been described as "the tool-making animal." The description is absolutely accurate; it is inclusive and exclusive. No non-human animal makes any form of implement to aid it in performing its daily work; and contrariwise every human tribe, however low its stage of savagery, makes use of more or less crude forms of implements. There must have been a time, to be sure, when there existed a man so low in intelligence that he had not put into execution the idea of making even the simplest tool. But the period when such a man existed so vastly antedates all records that it need not here concern us. For the purpose of classifying all existing men, and all the tribes of men of which history and pre-historic archæology give us any record, the definition of man as the tool-making animal is accurate and sufficient.

At first thought it might seem that an equally comprehensive definition might describe man as the working animal. But a moment's consideration shows the fallacy of such a suggestion. Man is, to be sure, the animal that works effectively, thanks to the implements with which he has learned to provide himself; but he shares with all animate creatures the task of laboring for his daily necessities. This is indeed a work-a-day world, and no creature can live in it without taking its share in that perpetual conflict which bodily necessities make imperative. Most lower animals confine their work to the mere securing of food, and to the construction of rude habitations. Some, indeed, go a step farther and lay up stores of food, in chance burrows or hollow trees; a few even manufacture relatively artistic and highly effective receptacles, as illustrated by the honeycomb made by the bees and their allies. Again, certain animals, of which the birds are the best representatives, construct temporary structures for the purpose of rearing their young that attain a relatively high degree of artistic perfection. The Baltimore oriole weaves a cloth of vegetable fibre that is certainly a wonderful texture to be made with the aid of claws and bill alone. It may be doubted whether human hands, unaided by implements, could duplicate it. But it is crude enough compared with even the coarsest cloth which barbaric races manufacture with the aid of implements.

So it is with any comparison of animal work with the work of man, in whatever field. The crudest human endeavor is superior to the best non-human efforts; and the explanation is found always in the fact that the ingenuity of man has enabled him to find artificial aids that add to his power of manipulation. So large a share have these artificial aids taken in man's evolution, that it has long been customary, in studying the development of civilization, to make the use of various types of implements a test of varying stages of human progress.

SCIENCE AND CIVILIZATION

The student of primitive life assures us, basing his statements on the archæological records, that there was a time when the most advanced of mankind had no tools made of better material than chipped stone. By common consent that time is spoken of as the Rough Stone Age.

We are told that then in the course of immeasurable centuries man learned to polish his stone implements, doubtless by rubbing them against another stone, or perhaps with the aid of sand, thus producing a new type of implement which has given its name to the Age of Smooth or Polished Stone.

Then after other long centuries came a time when man had learned to smelt the softer metals, and the new civilization which now supplanted the old, and, thanks to the new implements, advanced upon it immeasurably, is called the Age of Bronze.

At last man learned to accomplish the wonderful feat of smelting the intractable metal, iron, and in so doing produced implements harder, sharper, and cheaper than his implements of bronze; and when this crowning feat had been accomplished, the Age of Iron was ushered in.

By common consent, students of the history of the evolution of society accept these successive ages, each designated by the type of implements with which the world's work was accomplished, as representing real and definite stages of human progress, and as needing no better definition than that supplied by the different types of implements.

Could the archæologist trace the stream of human progress still farther back toward its source, he would find doubtless that there were several great epochal inventions preceding the time of the Rough Stone Age, each of which was in its way as definitive and as revolutionary in its effects upon society, as these later inventions which we have just named. To attempt to define them clearly is to enter the field of uncertainty, but two or three conjectures may be hazarded that cannot be very wide of the truth.

It is clear, for example, that if we go back in imagination to the very remotest ancestors of man that can be called human, we must suppose a vast and revolutionary stage of progress to have been ushered in by the first race of men that learned to make habitual use of the simplest implement, such as a mere club. When man had learned to wield a club and to throw a stone, and to use a stone held in the hand to break the shell of a nut, he had attained a stage of culture which augured great things for the future. Out of the idea of wielded club and hurled stone were to grow in time the ideas of hammer and axe and spear and arrow.

Then there came a time—no one dare guess how many thousands of years later—when man learned to cover his body with the skin of an animal, and thus to become in a measure freed from the thraldom of the weather. He completed his enfranchisement by learning to avail himself of the heat provided by an artificial fire. Equipped with these two marvelous inventions he was able to extend the hitherto narrow bounds of his dwelling-place, passing northward to the regions which at an earlier stage of his development he dared not penetrate. Under stress of more exhilarating climatic conditions, he developed new ideals and learned to overcome new difficulties; developing both a material civilization and the advanced mentality that is its counterpart, as he doubtless never would have done had he remained subject to the more pampering conditions of the tropics.

The most important, perhaps, of the new things which he was taught by the seemingly adverse conditions of an inhospitable climate, was to provide for the needs of a wandering life and of varying seasons by domesticating animals that could afford him an ever-present food supply. In so doing he ceased to be a mere fisher and hunter, and became a herdsman. One other step, and he had conceived the idea of providing for himself a supply of vegetable foods, to take the place of that which nature had provided so bountifully in his old home in the tropics. When this idea was put into execution man became an agriculturist, and had entered upon the high road to civilization.

All these stages of progress had been entered upon prior to the time of which the oldest known remains of the cave-dweller give us knowledge. It were idle to conjecture the precise sequence in which these earliest steps toward civilization were taken, and even more idle to conjecture the length of time which elapsed between one step and its successor. But all questions of precise sequence aside, it is clear that here were four or five great ages succeeding one to another, that marked the onward and upward progress of our primeval ancestor before he achieved the stage of development that enabled him to leave permanent records of his existence. And—what is particularly significant from our present standpoint—it is equally clear that each of the great ages thus vaguely outlined was dependent upon an achievement or an invention that facilitated the carrying out of that scheme of never-ending work which from first to last has been man's portion. How to labor more efficiently, more productively; how to produce more of the necessaries and of the luxuries that man's physical and mental being demands, with less expenditure of toil—that from first to last has been the ever-insistent problem. And the answer has been found always through the development of some new species of mechanism, some new labor-saving device, some ingenious manipulation of the powers of Nature.

If, turning from the hypothetical period of our primitive ancestor, we consider the sweep of secure and relatively recent history, we shall find that precisely the same thing holds. If we contrast the civilization of Old Egypt and Babylonia—the oldest civilizations of which we have any secure record—with the civilization of to-day, we shall find that the differences between the one and the other are such as are due to new and improved methods of accomplishing the world's work.

Indeed, if we view the subject carefully, it will become more and more evident that the only real progress that the historic period has to show is such as has grown directly from the development of new mechanical inventions. The more we study the ancient civilizations the more we shall be struck with their marvelous resemblance, as regards mental life, to the civilization of to-day. In their moral and spiritual ideals, the ancient Egyptians were as brothers to the modern Europeans. In philosophy, in art, in literature, the Age of Pericles established standards that still remain unexcelled. In all the subtleties of thought, we feel that the Greeks had reached intellectual bounds that we have not been able to extend.

But when, on the other hand, we consider the material civilization of the two epochs, we find contrasts that are altogether startling. The little world of the Greeks nestled about the Mediterranean, bounded on every side at a distance of a few hundred leagues by a terra incognita. The philosophers who had reached the confines of the field of thought, had but the narrowest knowledge of the geography of our globe. They traversed at best a few petty miles of its surface on foot or in carts; and they navigated the Mediterranean Sea, or at most coasted out a little way beyond the Pillars of Hercules in boats chiefly propelled by oars. By dint of great industry they produced a really astonishing number of books, but the production of each one was a long and laborious task, and the aggregate number indited during the Age of Pericles in all the world was perhaps not greater than an afternoon's output of a modern printing press.

In a word, these men of the classical period of antiquity, great as were their mental, artistic, and moral achievements, were as children in those matters of practical mechanics upon which the outward evidences of civilization depend. Should we find a race of people to-day in some hitherto unexplored portion of the earth—did such unexplored portions still exist—living a life comparable to that of the Age of Pericles, we should marvel no doubt at their artistic achievements, while at the same time regarding them as scarcely better than barbarians. Indeed this is more than unsupported hypothesis; for has it not been difficult for the Western world to admit the truly civilized condition of the Chinese, simply because that highly intellectual race of Orientals has not kept abreast of the Occidental changes in applied mechanics? Say what we will, this is the standard which we of the Western world apply as the test of civilization.

If, sweeping over in retrospect the history of the world since the time when the Egyptian and Babylonian civilizations were at their height, we attempt some such classification of the stages of progress as that which we a moment ago applied to pre-historic times, we shall be led to some rather startling conclusions. In the broadest view, it will appear that the age which ushered in the historic period continued unbroken by the advance of any great revolutionary invention throughout the long centuries of pre-Christian antiquity, and well into the so-called Middle Ages of our newer era. Then came the invention of gunpowder, or at least its introduction to the Western world—since the Chinaman here lays claim to vague centuries of precedence. Following hard upon the introduction of gunpowder, with its capacity to add to the destructive efficiency of man's most sinister form of labor, came a mechanism no less epoch-making in a far different field—the printing press.

But even these inventions, great as was their influence upon the progress of civilization, can scarcely be considered, it seems to me, as taking rank with the great epochal discoveries that gave their names to the preceding ages. Nor can any invention of the sixteenth or seventeenth century be hailed as really ushering in a new era. The invention for which that honor was reserved was a development of the eighteenth century; and did not come fully to its heritage until the early days of the nineteenth century. The invention was the application of steam to the purposes of mechanics. When this application was made, as wide a gap was crossed as that which separated the Stone Age from the Age of Metal; then the epoch in which the world was living when history begins was brought to a close, and a new era, the Age of Steam, was ushered in.

Scarcely had the world begun to adjust itself to the new conditions of the Age of Steam, when yet another power was made subservient to man's needs, and the Age of Steam was supplemented, not to say supplanted, by the Age of Electricity. Of course the new progressive movements did not necessarily imply elimination of old conditions; they imply merely the subordination of old powers to newer and better ones. Stone implements by no means ceased to have utility at once when metal implements came into vogue. Bronze long held its own against iron, and still has its utility. And iron itself finds but an added sphere of usefulness in the Age of Steam and Electricity.

All great changes are relatively slow. It is only as we look back upon them and view them in perspective that they seem cataclysmic. Gunpowder did not at once supplant the crossbow, and the cannon was long held to be inferior to the catapult. The printed book did not instantly make its way against the work of the scribe. Neither did the steam engine immediately supplant water power and the direct application of human labor. But in each case the new invention virtually rang the death knell of the old method from the hour of its inauguration, and the end was no less sure because it was delayed. And it requires no great powers of divination to foretell that in the coming age, the electric dynamo driven by water power may take the place of the steam engine. The Age of Steam may pass, with only at most a few generations of domination. And it is within the possibilities that the Age of Electricity will scarcely come into its own before it may be displaced by an Age of Radio-Activity. To press that point, however, would be to enter the field of prophecy, which is no part of my present purpose.

All that I have wished to point out is that for some thousands of years after man learned to make implements of iron, the industrial world and the human civilization that depends upon it, pursued a relatively static course, like a broad, sluggish current, with no new revolutionary discovery to impel it into new channels; and that then one revolutionary discovery succeeded another with bewildering suddenness, so that we of the early days of the twentieth century are farther removed, in an industrial way, from our forerunners of two hundred years ago, than those children of the eighteenth century were from the earliest civilization that ever developed on our globe. Indeed, this startling contrast would still hold true, were we to consider the newest era as compassing only the period of a single life. There are men living to-day who were born in that epoch when the steam engine was for the first time used to turn the wheels of factories. There are many men who can well remember the first practical application of steam to railway traffic. Hosts of men can remember when the first commercial message was transmitted by electricity along a wire. Even middle-aged men recall the first cable message that linked the old world with the new. And the application of the dynamo to the purposes of the world's work is an affair of but yesterday.

The historian of the future, casting his eye back across the long perspective of history, will find civilized man pursuing an even and unbroken course across the ages from the time of the pyramids of Egypt to about the time of the French Revolution. There will be no dearth of incident to claim his attention in the way of wars and conquests, and changing creeds, and the rise and fall of nations, each pursuing virtually the same course of growth and decay as all the others. But when he comes to the close of the eighteenth century, it will not be the social paroxysm of a nation, or the meteoric career of a Napoleon that will claim his attention so much as the introduction of that new method of utilizing the powers of Nature which found its expression in the mechanism called the steam engine.

If the name of any individual stands out as the great and memorable one of that epoch of transition, at which the static current of previous civilization changed suddenly to a Niagara-current of progress, it will be the name of the great scientific inventor, rather than that of the great military conqueror—the name of James Watt, rather than that of Napoleon.

The military conqueror had his day of surpassing glory and departed, to leave the world only a little worse than he found it. But the mechanical inventor left a heritage that was to add day by day to the wealth and happiness of humanity, supplying millions of artificial hands, and making possible such beneficent improvements as no previous age had dreamed of. Tasks that human hands had performed slowly, laboriously, and inadequately, were now to be performed swiftly, with ease, and well by the artificial hands provided with the aid of the new power. Where carts drawn by horses had toiled slowly across the land, and ships driven by the wind had drifted slowly through the waters, massive trains of cars were to hurtle to the four corners of the earth with inconceivable speed, and floating palaces were to course the waters with almost equal defiance to the limitations of time and space.

And then there came that still weirder conquest of time and space, wrought by the electric current. The moment when man first spoke with man from continent to continent in defiance of the oceans, marked the dawning of that larger day when all mankind shall constitute one brotherhood and all peoples but a single nation. Within a half century the sun of that new day has risen well above the horizon, and far sooner than even the optimist of to-day dare predict with certainty, it seems destined to reach its zenith.

But here again we verge upon the dangerous field of prophecy. Let us turn from it and cast an eye back across the most wonderful of centuries, contrasting the conditions of to-day in each of a half-dozen fields of the world's work, with the conditions that obtained at the close of the eighteenth century. Such a brief survey will show us perhaps more vividly than we could otherwise be shown, how vast has been the progress, how marvelous the development of civilization, in the short decades that have elapsed since the coming of the Age of Steam.

Let us pay heed first to the world of the agriculturist. Could we turn back to the days of our grandparents, we should find farming a very different employment from what it is to-day. For the most part the farmer operated but a few small fields; if he had thirty or forty acres of ploughed land, he found ample employment for his capacities. He ploughed his fields with the aid of either a yoke of oxen or a team of horses; he sowed his grain by hand; he cultivated his corn with a hoe; he reaped his oats and wheat with a cradle—a device but one step removed from a sickle; he threshed his grain with a flail; he ground such portion of it as he needed for his own use with the aid of water power at a neighboring mill; and such portion of it as he sold was transported to market, be it far or near, in wagons that compassed twenty or thirty miles a day at best. As regards live stock, each farmer raised a few cattle, sheep, and hogs, and butchered them to supply his own needs, selling the residue to a local dealer who supplied the non-agricultural portion of the neighborhood. Any live stock intended for a distant market was driven on foot across the country to its destination. Each town and city, therefore, drew almost exclusively for its supply from the immediately surrounding country.

To-day the small farmer has become almost obsolete, and the farms of the eastern states that were the nation's chief source of supply a century ago are largely allowed to lie fallow, it being no longer possible to cultivate them profitably in competition with the rich farm lands of the middle west. In that new home of agriculture, the farm that does not comprise two or three hundred acres is considered small; and large farms are those that number their acres by thousands. The soil is turned by steam ploughs; the grain is sown with mechanical seeders and planters; the corn is cultivated with a horse-drawn machine, having blades that do the work of a dozen men; harvesters drawn by three or four horses sweep over the fields and leave the grain mechanically tied in bundles; the steam thresher places the grain in sacks by hundreds of bushels a day; and this grain is hurried off in steam cars to distant mills and yet more distant markets.

Meantime the raising of live stock has become a special department, with which the farmer who deals in cereals often has no concern. The cattle roam over vast pastures and are herded in the winter for fattening in great droves, and protected from the cold in barns that, when contrasted with the sheds of the old-time farmer, seem almost palatial. When in marketable condition, cattle are no longer slaughtered at the farm, but are transported in cars to one of the few great centres, chief of which are the stock yards of Chicago and of Kansas City. At these centres, slaughter houses and meat-packing houses of stupendous magnitude have been developed, capable of handling millions of animals in a year. From these centres the meat is transported in refrigerator cars to the seaboards, and in refrigerator ships to all parts of the world. Beef that grew on the ranges of the far west may thus be offered for sale in the markets of New England villages, at a price that prohibits local competition.

A more radical metamorphosis in agricultural conditions than all this implies could not well be conceived. And when we recall once more that the agricultural conditions that obtained at the beginning of the nineteenth century were closely similar to those that obtained in each successive age for a hundred preceding centuries, we shall gain a vivid idea of the revolutionizing effects of new methods of work in the most important of industries. It is little wonder that in this short time the world has not solved to the satisfaction of the economists all the new problems thus so suddenly developed.

Turn now to the manufacturing world. In the days of our great-grandparents almost every household was a miniature factory where cotton and wool were spun and the products were woven into cloth. It was not till toward the close of the eighteenth century—just at the time when Watt was perfecting the steam engine—that Arkwright developed the spinning-frame, and his successors elaborated the machinery that made possible the manufacture of cloth in wholesale quantities; and the nineteenth century was well under way before the household production of cloth had been entirely supplanted by factory production. It is nothing less than pitiful to contemplate in imagination our great-great-grandmothers—and all their forebears of the long centuries—drudging away day after day, year in and year out, at the ceaseless task of spinning and weaving—only to produce, as the output of a lifetime of labor, a quantity of cloth equivalent perhaps to what our perfected machine, driven by steam, and manipulated by a factory girl, produces each working hour of every day. Similarly, carpets and quilts were of home manufacture; so were coats and dresses; and shoes were at most the product of the local shoemaker around the corner.

In the kitchen, food was cooked over the coals of a great fireplace or in the brick oven connected with that fireplace. Meat was supplied from a neighboring farm; eggs were the product of the housewife's own poultry yard; the son or daughter of the farmer milked the cow and drove her to and from the pasture; the milk was "set" in pans in the cellar—on a swinging shelf, preferably, to make it inaccessible to the rats; and twice a week the cream was made into butter in a primitive churn, the dasher of which was operated by the vigorous arm of the housewife herself, or by the unwilling arms of some one of her numerous progeny.

To give variety to the dietary, fruits grown in the local garden or orchard were preserved, each in its season, by the industrious housewife, and stored away in the capacious cellar; where also might be found the supply of home-grown potatoes, turnips, carrots, parsnips, and cabbages to provide for the needs of the winter. Fuel to supply the household needs, both for cooking and heating, was cut in the neighboring woodland, and carefully corded in the door-yard, where it provided most uncongenial employment for the youth of the family after school hours and of a Saturday afternoon.

The ashes produced when this wood was burned in the various fireplaces, were not wasted, but were carefully deposited in barrels, from which in due course lye was extracted by the simple process of pouring water over the contents of the barrel. Meantime scraps of fat from the table were collected throughout the winter and preserved with equal care; and in due course on some leisure day in the springtime—heaven knows how a leisure day was ever found in such a scheme of domestic economy!—the lye drawn from the ash-barrels and the scraps of fat were put into a gigantic kettle, underneath which a fire was kindled; with the result that ultimately a supply of soft soap was provided the housewife, with which her entire establishment, progeny included, could be kept in a state of relative cleanness.

The reader of these pages has but to cast his eye about him in the household in which he lives, and contrast the conditions just depicted with those of his every-day life, to realize what change has come over the aspects of household economy in the course of a short century. Nor need he be told in each of the various departments of which the activities are here outlined, that the changes which he observes have been due to the application of machinery in all the essential lines of work in question. We need not pause to detail the multitudinous devices for the economy of household labor which owe their origin to the same agency. There still remains, to be sure, enough of drudgery in the task of the housewife; yet her most strenuous day seems a mere playtime in comparison with the average day of her maternal forebear of three or four generations ago.

But we must not here pause for further outlines of a subject which it is the purpose of this and succeeding volumes to explicate in detail. All our succeeding chapters will but make it more clear how marvelous are the elaborations of method and of mechanism through which the world's work of to-day is accomplished. We shall consider first the mechanical principles that underlie work in general, passing on to some of the principal methods of application through which the powers of Nature are made available. We shall then take up in succession the different fields of industry. We shall ask how the work of the agriculturist is done in the modern world; how the multitudinous lines of manufacture are carried out; how transportation is effected; we shall examine the modus operandi of the transmission of ideas; we shall even consider that destructive form of labor which manifests itself in the production of mechanisms of warfare. As we follow out the stories of the all-essential industries we shall be led to realize more fully perhaps than we have done before, the meaning of work in its relations to human development; and in particular the meaning of modern work, as carried out with the aid of modern mechanical contrivances, in its relations to modern civilization.

The full force of these relations may best be permitted to unfold itself as the story proceeds. There is, however, one fundamental principle which I would ask the reader to bear constantly in mind, as an aid to the full appreciation of the importance of our subject. It is that in considering the output of the worker we have constantly to do with one form or another of property, and that property is the very foundation-stone of civilization. "It is impossible," says Morgan, in his work on Ancient Society, "to overestimate the influence of property in the civilization of mankind. It was the power that brought the Aryan and Semitic nations out of barbarism into civilization. The growth of the idea of property in the human mind commenced in feebleness and ended in becoming its master passion. Governments and laws are instituted with primary reference to its creation, protection, and enjoyment. It introduced human slavery in its production; and, after the experience of several thousand years, it caused the abolition of slavery upon the discovery that the freeman was a better property-making machine." If, then, we recall that without labor there is no property, we shall be in an attitude of mind to appreciate the importance of our subject; we shall realize, somewhat beyond the bounds of its more tangible and sordid relations, the essential dignity, the fundamental importance—in a word, the true meaning—of Work.

Undoubtedly there is a modern tendency to accept this view of the dignity of physical labor. At any rate, we differ from the savage in thinking it more fitting that man should toil than that his wife should labor to support him—though it cannot be denied that even now the number of physical toilers among women greatly exceeds the number of such toilers among men. But in whatever measure we admit this attitude of mind, there can be no question that it is exclusively a modern attitude. Time out of mind, physical labor has been distasteful to mankind, and it is a later development of philosophy that appreciates the beneficence of the task so little relished.

The barbarian forces his wife to do most of the work, and glories in his own freedom. Early civilization kept conquered foes in thraldom, developing an hereditary body of slaves, whose function it was to do the physical work.

The Hebrew explained the necessity for labor as a curse imposed upon Father Adam and Mother Eve. Plato and Aristotle, voicing the spirit of the Greeks, considered manual toil as degrading.

To-day we hear much of the dignity of labor; but if we would avoid cant we must admit that now—scarcely less than in all the olden days—the physical toiler is such because he cannot help himself. Few indeed are the manual laborers who know any other means of getting their daily bread than that which they employ. The most strenuous advocates of the strenuous life are not themselves tillers of the soil or workers in factories or machine shops.

The farm youth of intelligence does not remain a farmer; he goes to the city, and we find him presently at the head of a railroad or a bank, or practising law or medicine. The more intelligent laborer becomes finally a foreman, and no longer handles the axe or sledge. We should think it grotesque were we to see a man of intellectual power obstinately following a pursuit that cost him habitual physical toil. When now and then a Tolstoi offers an exception to this rule, we feel that he is at least eccentric; and we may be excused the doubt whether he would follow the manual task cheerfully if he did not know that he could at any moment abandon it. It is because he knows that the world understands him to be only a dilettante that he rejoices in his task.

After all, then, judged by the modern practice, rather than by the philosopher's precept, the old Hebrew and Greek ideas were not so far wrong. Using the poetical language which was so native to them, it might be said that the necessity for physical labor is a curse—a disgrace.

A partial explanation of this may be found in the fact that the most uncongenial tasks are also the worst paid, while the congenial tasks command the high emoluments. Generally speaking there is no distinction between one laborer and another in the same field—except where the eminently fair method of piece work can be employed. Even the skilled laborer is usually paid by the day, and the amount he is to receive is commonly fixed by a Union regardless of his efficiency as compared with other laborers of the same class. And there is no possibility of his receiving any such sums as the man who plans the work, but does nothing with his own hands.

It has always been so. Just as "those who think must govern those that toil," so the thinker must command the high reward. Partly this is because man, considered as a mere toiler, is so relatively inefficient a worker. When he strives to work with his hands, his effort is but a pitiful one; he can by no possibility compete (as regards mere quantity of labor) with the ox and the horse. He is impatient of his own puerile efforts. It is only when he brings the products of ingenuity to his aid that he is able to show his superiority, and to justify his own egotism. So it is that in every age he has striven to find means of adding to his feeble powers of body through the use of his relatively gigantic powers of mind. And in proportion as he thus is able to "make his head work for his hands" as the saying goes, he verges toward the heights of civilization. To accomplish this more and more fully has ever been the task of science as applied to the industries.

It will be our object in the ensuing chapters to inquire how far science has accomplished the protean task thus set for it. We shall see that much has been done; but that much still remains to be done. In proportion as the problems are unsolved, science is reproached for its shortcomings—and stimulated to new efforts.

In proportion as labor has been minimized and production increased—in just that proportion has science justified itself; and in the same proportion has the Conquest of Nature been carried toward completion.

[II]

HOW WORK IS DONE

The word energy implies capacity to do work. Work, considered in the abstract, consists in the moving of particles of matter against some opposing force, or in aid of previously acting forces. In the last analysis, all energy manifests itself either as a push or as a pull. But there is a modification of push and pull which is familiar to everyone in practice under the name of prying. Illustrations may be seen on every hand, as when a workman pries up a stone, or when a housewife pries up a tack with the aid of a hammer. The principle here involved is that of the lever—a principle which in its various practical modifications is everywhere utilized in mechanics. Very seldom indeed is the direct push or pull utilized; since the modified push or pull, as represented by the lever in its various modifications of pulley, ratchet-wheel, and the like, has long been known to meet the needs of practical mechanics.

The very earliest primitive man who came to use any implement whatever, though it were only a broken stick, must have discovered the essential principle of the lever, though it is hardly necessary to add that he did not know his discovery by any such high-sounding title. What he did know, from practical experience, was that with the aid of a stick he could pry up stones or logs that were much too heavy to be lifted without this aid.

This practical knowledge no doubt sufficed for a vast number of generations of men who used the lever habitually, without making specific study of the relations between the force expended, the lengths of the two ends of the lever, and the weight raised. Such specific experiments were made, however, more than two thousand years ago by the famous Syracusan, Archimedes. He discovered—or if some one else had discovered it before him, he at least recorded and so gains the credit of discovery—the specific laws of the lever, and he also pointed out that levers, all acting on the same principle, may be different as to their practical mechanism in three ways.

First, the fulcrum may lie between the power and the weight, as in the case of the balance with which we were just experimenting. This is called a lever of the first class, and familiar illustrations of it are furnished by the poker, steelyard, or a pair of scissors. The so-called extensor muscles of the body—those for example, that cause the arm to extend—act on the bones in such a way as to make them levers of this first class.

The second type of lever is that in which the weight lies between the force and the fulcrum, as illustrated by the wheelbarrow, or by an ordinary door.

In the third class of levers the power is applied between weight and fulcrum, as illustrated by a pair of tongs, the treadle of a lathe, or by the flexor muscles of the arm, operating upon the bones of the forearm.

But in each case, let it be repeated, precisely the same principles are involved, and the same simple law of the relations between positions of power, weight, and fulcrum are maintained. The practical result is always that a weight of indefinite size may be moved by a power indefinitely long. If one arm of the lever is ten times as long as the other, the power of one pound will lift or balance a ten-pound weight; if the one arm is a thousand times as long as the other the power of one pound will lift or balance a thousand pounds. If the long arm of the lever could be made some millions of miles in length, the power that a man could exert would balance the earth.

How fully Archimedes realized the possibilities of the lever is illustrated in the classical remark attributed to him, that, had he but a fulcrum on which to place his lever, he could move the world. As otherwise quoted, the remark of Archimedes was that, had he a place on which to stand, he could move the world, a remark which even more than the other illustrates the full and acute appreciation of the laws of motion; since, as we have already pointed out, action and reaction being equal, the most infinitesimal push must be considered as disturbing even the largest body.

Tremendous as is the pull of gravity by which the earth is held in its orbit, yet the smallest push, steadily applied from the direction of the sun, would suffice ultimately to disturb the stability of our earth's motion, and to push it gradually through a spiral course farther and farther away from its present line of elliptical flight. Or if, on the other hand, the persistent force were applied from the side opposite the sun, it would suffice ultimately to carry the earth in a spiral course until it plunged into the sun itself. Indeed it has been questioned in modern times whether it may not be possible that precisely this latter effect is gradually being accomplished, through the action of meteorites, some millions of which fall out of space into the earth's atmosphere every day. If these meteorites were uniformly distributed through space and flying in every direction, the fact that the sun screens the earth from a certain number of them, would make the average number falling on the side away from the sun greater, and thus would in the course of ages produce the result just suggested. All that could save our earth from such a fate would be the operation of some counteracting force. Such a counteracting force is perhaps found in solar radiation. It may be added that the distribution of meteorites in space is probably too irregular to make their influence on the earth predicable in the present state of science; but the principle involved is no less sure.

WHEELS AND PULLEYS

Returning from such theoretical applications of the principle of motion, to the practicalities of every-day mechanisms, we must note some of the applications through which the principle of the lever is made available. Of these some of the most familiar are wheels, and the various modifications of wheels utilized in pulleys and in cogged and bevelled gearings. A moment's reflection will make it clear that the wheel is a lever of the first class, of which the axle constitutes the fulcrum. The spokes of the wheel being of equal length, weights and forces applied to opposite ends of any diameter are, of course, in equilibrium. It follows that when a wheel is adjusted so that a rope may be run about it, constituting a simple pulley, a mechanism is developed which gives no gain in power, but only enables the operator to change the direction of application of power. In other words, pound weights at either end of a rope passed about a simple pulley are in equilibrium and will balance each other, and move through equal distances in opposite directions.

HORSE AND CATTLE POWER.

The large picture shows a model of a familiar mechanism for utilizing horse power. The small picture shows a similar apparatus in actual operation, actuated by cattle, in contemporary Brittany.

If, however, two or more pulley wheels are connected, to make the familiar apparatus of a compound pulley, we have accomplished by an interesting mechanism a virtual application of the principle of the long and short arm of the lever, and the relations between the weight at the loose end of the rope and the weight attached to the block which constitutes virtually the short end of the lever, may be varied indefinitely, according to the number of pulley-wheels that are used. A pound weight may be made to balance a thousand-pound weight; but, of course, our familiar principle still holding, the pound weight must move through a distance of a thousand feet in order to move a thousand-pound weight through a distance of one foot. Familiar illustrations of the application of this principle may be seen on every hand; as when, for example, a piano or a safe is raised to the upper window of a building by the efforts of men whose power, if directly expended, would be altogether inefficient to stir the weight.

The pulley was doubtless invented at a much later stage of human progress than the simple lever. It was, however, well known to the ancients. It was probably brought to its highest state of practical perfection by Archimedes, whose experiments are famous through the narrative of Plutarch. It will be recalled that Archimedes amazed the Syracusan general by constructing an apparatus that enabled him, sitting on shore, to drag a ponderous galley from the water. Plutarch does not describe in detail the apparatus with which this was accomplished, but it is obvious from his description of what took place, that it must have been a system of pulleys.

It will be observed that the pulley is a mechanism that enables the user to transmit power to a distance. But this indeed is true in a certain sense of every form of lever. Numberless other contrivances are in use by which power is transmitted, through utilization of the same principle of the lever, either through a short or through a relatively long distance. A familiar illustration is the windlass, which consists of a cylinder rotating on an axis propelled by a long handle, a rope being wound about the cylinder. This is a lever of the second class, the axis acting as fulcrum, and the rope operating about the circumference of the cylinder typifying the weight, which may be actually at a considerable distance, as in the case of the old-fashioned well with its windlass and bucket, or of the simple form of derrick sometimes called a sheerlegs.

OTHER MEANS OF TRANSMITTING POWER

Power is transmitted directly from one part of a machine to another, in the case of a great variety of machines, with the aid of cogged gearing wheels of various sizes. The modifications of detail in the application of these wheels may be almost infinite, but the principle involved is always the same. The case of two wheels toothed about the circumference, the teeth of the two wheels fitting into one another, illustrates the principle involved. A consideration of the mechanism will show that here we have virtually a lever fixed at both ends, represented by the radii of the two wheels, the power being applied through the axle of one wheel, and the weight, for purposes of calculation, being represented by the pressure of the teeth of one wheel upon those of the other. So this becomes a lever of the second class, and the relations of power between the two wheels are easily calculated from the relative lengths of the radii. If, for example, one radius is twice as long as the other, the transmission of power will be, obviously, in the proportion of two to one, and meantime the distance traversed by the circumference of one wheel will be twice as great as that traversed by the other.

A modification of the toothed wheel is furnished by wheels which may be separated by a considerable distance, and the circumferences of which are connected by a belt or by a chain. The principle of action here is precisely the same, the belt or chain serving merely as a means of lengthening out our lever. The relative sizes of the wheels, and not the length of the belt or chain, is the determining factor as regards the relative forces required to make the wheels revolve.

It is obvious all along, of course, since action and reaction are equal, that all of the relations in question are reciprocal. When, for example, we speak of a pound weight on the long end of a lever balancing a ten-pound weight on the short end, it is equally appropriate to speak of the ten-pound weight as balancing the one-pound weight. Similarly, when power is applied to the lever, it may be applied at either end. Ordinarily, to be sure, the power is applied at the long end, since the object is to lift the heavy weight; but in complicated machinery it quite as often happens that these conditions are reversed, and then it becomes desirable to apply strong power to the short end of the lever, in order that the relatively small weight may be carried through the long distance. In the inter-relations of gearing wheels, such conditions very frequently obtain, practical ends being met by a series of wheels of different sizes. But the single rule, already so often outlined, everywhere holds—wherever there is gain of power there is loss of distance, and we can gain distance only by losing power. The words gain and loss in this application are in a sense misnomers, since, as we have already seen, gain and loss are only apparent, but their convenience of application is obvious.

A familiar case in which there is first loss of speed and gain of power, and then gain of speed at the expense of power in the same mechanism, is furnished by the bicycle, where (1) the crank shaft turns the sprocket wheel that constitutes a lever of the second class with gain of power; where (2) power is further augmented through transmission from the relatively large sprocket wheel to the small sprocket of the axle; and where (3) there is great loss of power and corresponding gain of speed in transmitting the force from the small sprocket wheel at the axle to the rubber rim of the bicycle proper, this last transmission representing a lever of the third class. The net gain of speed is tangibly represented by the difference in distance traversed by the man's feet in revolving the pedals, and the actual distance covered by the bicycle.

INCLINED PLANES AND DERRICKS

A less obvious application of the principle of reciprocal equivalence of distance and weight is furnished by the inclined plane, a familiar mechanism with the aid of which a great gain of power is possible. The inclined plane, like the lever, has been known from remotest antiquity. Its utility was probably discovered by almost the earliest builders. Diodorus Siculus tells us that the great pyramids of Egypt were constructed with the aid of inclined planes, based on a foundation of earth piled about the pyramids. Diodorus, living at a period removed by some thousands of years from the day of the building of the pyramids, may or may not have voiced and recorded an authentic tradition, but we may well believe that the principle of the inclined plane was largely drawn upon by the mechanics of old Egypt, as by later peoples.

The law of the inclined plane is that in order to establish equilibrium between two weights, the one must be to the other as the height of the inclined plane is to its length. The steeper the inclined plane, therefore, the less will be the gain in power; a mechanical principle which familiar experience or the simplest experiment will readily corroborate.

In its elemental form the inclined plane is not used very largely in modern machinery, but its modified form of the wedge and the screw have more utility. The screw, indeed, which is obviously an inclined plane adjusted spirally about a cylinder or a cone, is familiar to everyone, and is constantly utilized in applying power.

The crane or derrick furnishes a familiar but relatively elaborate illustration of a mechanism for the transmission of power, in which all the various devices hitherto referred to are combined, without the introduction of any new principle.

Derricks have been employed from a very early day. The battering-rams of the ancient Egyptians and Babylonians, for example, were virtually derricks; and no doubt the same people used the device in raising stones to build their temples and city walls, and in putting into position such massive sculptures as the obelisks of Egypt and the monster graven bulls and lions of Nineveh and Babylon.

CRANES AND DERRICKS.

The upper figure shows a floating derrick, the lower right-hand figure a combined derrick and weighing machine, and the lower left-hand figure a so-called sheerlegs, which is a simple derrick and windlass operated by hand or by steam power with the aid of compound pulleys.

The modern derrick, made of steel, and operated by steam or electricity, capable of lifting tons, yet absolutely obedient to the hand of the engineer, is a really wonderful piece of mechanism. A steam-scoop, for example, excavating a gravel bank, seems almost a thing of intelligence; as it gores into the bank scooping up perhaps a half ton of earth, its upward sweeping head reminds one of an angry bull. Then as it swings leisurely about and discharges its load at just the right spot into an awaiting car, its hinged bottom swings back and forth two or three times before closing, with curious resemblance to the jaw of a dog; the similarity being heightened by the square bull-dog-headed shape of the scoop itself. Yet this remarkable contrivance, with all its massive steel beams and chains and cog wheels, employs no other principles than the simple ones of lever and pulley and inclined plane that we have just examined. The power that must be applied to produce a given effect may be calculated to a nicety. The capacities of the machine are fully predetermined in advance of its actual construction. But of course this is equally true of every other form of power-transmitter with which the modern mechanical engineer has to deal.

FRICTION

In making such calculations, however, there is an additional element which the engineer must consider, but which we have hitherto disregarded. In all methods of transmission of power, and indeed in all cases of the contact of one substance with another, there is an element of loss through friction. This is due to the fact that no substance is smooth except in a relative sense. Even the most highly polished glass or steel, when viewed under the microscope, presents a surface covered with indentations and rugosities. This granular surface of even seemingly smooth objects, is easily visualized through the analogy of numberless substances that are visibly rough. Yet the vast practical importance of this roughness is seldom considered by the casual observer. In point of fact, were it not for the roughened surface of all materials with which we come in contact, it would be impossible for any animal or man to walk, nor could we hold anything in our hands. Anyone who has attempted to handle a fish, particularly an eel, fresh from the water, will recall the difficulty with which its slippery surface was held; but it may not occur to everyone who has had this experience that all other objects would similarly slip from the hand, had their surfaces a similar smoothness. The slippery character of the eel is, of course, due in large part to the relatively smooth surface of its skin, but partly also to the lubricant with which it is covered. Any substance may be rendered somewhat smoother by proper lubrication; it is necessary, however, that the lubricant should be something which is not absorbed by the substance. Thus, wood is given increased friction by being moistened with oil, but, on the other hand, is made slippery if covered with graphite, soap, or any other fatty substances that it does not absorb.

Recalling the more or less roughened surface of all objects, the source of friction is readily understood. It depends upon the actual jutting of the roughened surfaces, one upon the other. It virtually constitutes a force acting in opposition to the motion of any two surfaces upon each other. As between any different materials, under given conditions, it varies with the pressure, in a definite and measurable rate, which is spoken of as the coefficient of friction for the particular substances. It is very much greater where the two substances slide over one another than where the one rolls upon the other, as in the case of the wheel. The latter illustrates what is called rolling friction, and in practical mechanics it is used constantly to decrease the loss—as, for example, in the wheels of wagons and cars. The use of lubricants to decrease friction is equally familiar. Without them, as everyone knows, it would be impossible to run any wheel continuously upon an axle at high speed for more than a very brief period, owing to the great heat developed through friction. Friction is indeed a perpetual antagonist of the mechanician, and we shall see endless illustrations of the methods he employs to minimize its influence. On the other hand, we must recall that were it rendered absolutely nil, his machinery would all be useless. The car wheel, for example, would revolve indefinitely without stirring the train, were there absolutely no friction between it and the rail.

AVAILABLE SOURCES OF ENERGY

We have pointed out that every body whatever contains a certain store of energy, but it has equally been called to our attention that, in the main, these stores of energy are not available for practical use. There are, however, various great natural repositories of energy upon which man is able to draw. The chief of these are, first, the muscular energy of man himself and of animals; second, the energy of air in motion; third, the energy of water in motion or at an elevation; and fourth, the molecular and atomic energies stored in coal, wood, and other combustible materials. To these we should probably add the energy of radio-active substances—a form of energy only recently discovered and not as yet available on a large scale, but which may sometime become so, when new supplies of radio-active materials have been discovered. It will be the object of succeeding chapters to point out the practical ways in which these various stores of energy are drawn upon and made to do work for man's benefit.

[III]

THE ANIMAL MACHINE

The muscular system is not only the oldest machine in existence, but also the most complex. Moreover, it is otherwise entitled to precedence, for even to-day, in this so-called age of steam and electricity, the muscular system remains by far the most important of all machines. In the United States alone there are some twenty million horses doing work for man; and of course no machine of any sort is ever put in motion or continues indefinitely in operation without aid supplied by human muscles. All in all, then, it is impossible to overestimate the importance of this muscular machine which is at once the oldest and the most lasting of all systems of utilizing energy.

The physical laws that govern the animal machine are precisely similar to those that are applied to other mechanisms. All the laws that have been called to our attention must therefore be understood as applying fully to the muscular mechanism. But in addition to these the muscular system has certain laws or methods of action of its own, some of which are not very clearly understood.

The prime mystery concerning the muscle is its wonderful property of contracting. For practical purposes we may say that it has no other property; the sole function of the muscle is to contract. It can, of course, relax, also, to make ready for another contraction, but this is the full extent of its activities. A microscopic examination of the muscle shows that it is composed of minute fibres, each of which on contraction swells up into a spindle shape. A mass of such fibres aggregated together constitutes a muscle, and every muscle is attached at either extremity, by means of a tendon, to a bone. Both extremities of a muscle are never attached to the same bone—otherwise the muscle would be absolutely useless. Usually there is only a single bone between the two ends of a muscle, but in exceptional cases there may be more. As a rule, the main body of a muscle lies along the bone to which one end of it is attached, the other end of the muscle being attached to the contiguous bone placed not far from the point. The first bone, then, serves as a fulcrum on which the second bone moves as a lever, and, as already pointed out, the familiar laws of the lever operate here as fully as in the inanimate world. But a moment's reflection will make it clear that the object effected by this mechanism is the increase of motion with relative loss of energy. In other words, the muscular force is applied to the short end of the lever, and a far greater expenditure of force is required when the muscle contracts than the power externally manifested would seem to indicate.

A moment's consideration of the mechanism of the arm, having regard to the biceps muscle which flexes the elbow, will make this clear. If a weight is held in the hand it is perhaps twelve inches from the elbow. If, while holding the weight, you will grasp the elbow with the other hand, you will feel the point of attachment of the biceps, and discover that it does not seem to be, roughly speaking, more than about an inch from the joint. Obviously, then, if you are lifting a pound weight, the actual equivalent of energy expended by the contracting biceps must be twelve pounds. But, in the meantime, when the pound weight in your hand moves through the space of one inch, the muscle has contracted by one-twelfth of an inch; and you may sweep the weight through a distance of two feet by utilizing the two-inch contraction, which represents about the capacity of the muscle.

A similar consideration of the muscles of the legs will show how the muscular system which is susceptible of but trifling variation in size, gives to the animal great locomotive power. With the aid of a series of levers, represented by the bones of our thighs, legs, and feet, we are able to stride along, covering three or four feet at each step, while no set of the muscles that effect this propulsion varies in length by more than two or three inches. It appears, then, that the muscular system gives a marvelous illustration of capacity for storing energy in a compact form and utilizing it for the development of motion.

THE TWO TYPES OF MUSCLES

The muscles of animals and men alike are divided into two systems, one called voluntary, the other involuntary. The voluntary muscles, as their name implies, are subject to the influence of the will, and under ordinary conditions contract in response to the voluntary nervous impulses. Certain sets of them, indeed, as those having to do with respiration, have developed a tendency to rhythmical action through long use, and ordinarily perform their functions without voluntary guidance. Their function may, however, become voluntary when attention is directed toward it, and is then subject to the action of the will within certain bounds. Should a voluntary attempt be made, however, to prevent their action indefinitely, the so-called reflex mechanism presently asserts itself. All of which may be easily attested by anyone who will attempt to stop breathing. All systems of voluntary muscles are subject to the influence of habit, and may assume activities that are only partially recognized by consciousness. As an illustration in point, the muscles involved in walking come, in the case of every adult, to perform their function without direct guidance of the will. Such was not the case, however, in the early stage of their development, as the observation of any child learning to walk will amply demonstrate. In the case of animals, however, even those muscles are so under the impress of hereditary tendencies as to perform their functions spontaneously almost from the moment of birth. These, however, are physiological details that need not concern us here. It suffices to recall that the voluntary muscles may be directed by the will, and indeed are always under what may be termed subconscious direction, even when the conscious attention is not directed to them.

The strictly involuntary muscles, however, are placed absolutely beyond control of the will. The most important of these muscles are those that constitute the heart and the diaphragm, and that enter into the substance of the walls of blood vessels, and of the abdominal organs. It is obvious that the functioning of these important organs could not advantageously be left to the direction of the will; and so, in the long course of evolution they have learned, as it were, to take care of themselves, and in so doing to take care of the organism, to the life of which they are so absolutely essential. As the physiologist views the matter, no organism could have developed which did not correspondingly develop such involuntary action of the vital organs. It will be seen that the involuntary muscles differ from the voluntary muscles in that they are not connected with bones. Instead of being thus attached to solid levers, they are annular in structure, and in contracting virtually change the size of the ring which their substance constitutes. Each fibre in contracting may be thought of as pulling against other fibres, instead of against a bony surface, and the joint action changes the size of the organ, as is obvious in the pulsing of the heart.

Though the rhythmical contractions of the involuntary muscles are independent of voluntary control, it must not be supposed that they are independent of the control of the central nervous mechanism. On the contrary, the nerve supply sent out from the brain to the heart and to the abdominal organs is as plentiful and as important as that sent to the voluntary muscles. There is a centre in the brain scarcely larger than the head of a pin, the destruction of which will cause the heart instantly to cease beating forever. From this centre, then, and from the other centres of the brain, impulses are constantly sent to the involuntary muscles, which determine the rate of activity. Nor are these centres absolutely independent of the seat of consciousness, as anyone will admit who recalls the varied changes in the heart's action under stress of varying emotions.

That the voluntary muscles are controlled by the central nervous mechanism needs no proof beyond the appeal to our personal experiences of every moment. You desire some object that lies on the table in front of you, and immediately your hand, thanks to the elaborate muscular mechanism, reaches out and grasps it. And this act is but typical of the thousand activities that make up our every-day life. Everyone is aware that the channel of communication between the brain and the muscular system is found in a system of nerves, which it is natural now-a-days to liken to a system of telegraph wires. We speak of the impulse generated in the brain as being transmitted along the nerves to the muscle, causing that to contract. We are even able to measure the speed of transfer of such an impulse. It is found to move with relative slowness, compassing only about one hundred and twelve feet per second, being in this regard very unlike the electric current with which it is so often compared. But the precise nature of this impulse is unknown. Its effect, however, is made tangible in the muscular contraction which it is its sole purpose to produce. The essential influence of the nerve impulse in the transaction is easily demonstrable; for if the nerve cord is severed, as often happens in accidents, the muscle supplied by that nerve immediately loses its power of voluntary contraction. It becomes paralyzed, as the saying is.

THE NATURE OF MUSCULAR ACTION

Paying heed, now, to the muscle itself, it must be freely admitted that, in the last analysis, the activities of the substance are as mysterious and as inexplicable as are those involved in the nervous mechanism. It is easy to demonstrate that what we have just spoken of as a muscle fibre consists in reality of a little tube of liquid protoplasm, and that the change in shape of this protoplasm constitutes the contraction of which we are all along speaking. But just what molecular and atomic changes are involved in this change of form of the protoplasm, we cannot say. We know that the power to contract is the one universal attribute of living protoplasm. This power is equally wonderful and equally inexplicable, whether manifested in the case of the muscle cell or in the case of such a formless single-celled creature as the amœba. When we know more of molecular and atomic force, we may perhaps be able to form a mental picture of what goes on in the structure of protoplasm when it thus changes the shape of its mass. Until then, we must be content to accept the fact as being the vital one upon which all the movements of animate creatures depend.

But if, here as elsewhere, the ultimate activities of molecules and atoms lie beyond our ken, we may nevertheless gain an insight into the nature of the substances involved. We know, for example, that the chief constituents of all protoplasm are carbon, hydrogen, oxygen, and nitrogen; and that with these main elements there are traces of various other elements such as iron, sulphur, phosphorus, and sundry salts. We know that when the muscle contracts some of these constituents are disarranged through what is spoken of as chemical decomposition, and that there results a change in the substance of the protoplasm, accompanied by the excretion of a certain portion of its constituents, and by the liberation of heat. Carbonic acid gas, for example, is generated and is swept away from the muscular tissues in the ever active bloodstreams, to be carried to the lungs and there expelled—it being a noxious poison, fatal to life if retained in large quantities. Equally noxious are other substances such as uric acid and its compounds, which are also results of the breaking down of tissue that attends muscular action. In a word, there is an incessant formation of waste products, due to muscular activity, the removal of which requires the constant service of the purifying streams of blood and of the various excretory organs.

But this constant outflow of waste products from the muscle necessitates, of course, in accordance with the laws of the conservation of matter and of energy, an equally constant supply of new matter to take the place of the old. This supply of what is virtually fuel to be consumed, enabling the muscle to perform its work, is brought to the muscle through the streams of blood which flow from the heart in the arterial channels, and in part also through the lymphatic system. The blood itself gains its supply from the digestive system and from the lungs. The digestive system supplies water, that all-essential diluent, and a great variety of compounds elaborated into the proper pabulum; while the vital function of the lungs is to supply oxygen, which must be incessantly present in order that the combustion which attends muscular activity may take place. What virtually happens is that fuel is sent from the digestive system to be burned in the muscular system, with the aid of oxygen brought from the lungs.

In this view, the muscular apparatus is a species of heat engine. In point of fact, it is a curiously delicate one as regards the range of conditions within which it is able to act. The temperature of any given organism is almost invariable; the human body, for example, maintains an average temperature of 98-2/5 degrees, Fahrenheit. The range of variation from this temperature in conditions of health is rarely more than a fraction of a degree; and even under stress of the most severe fever the temperature never rises more than about eight degrees without a fatal result. That an organism which is producing heat in such varying quantities through its varying muscular activities should maintain such an equilibrium of temperature, would seem one of the most marvelous of facts, were it not so familiar.

The physical means by which the heat thus generated is rapidly given off, on occasion, to meet the varying conditions of muscular activity, is largely dependent upon the control of the blood supply, in which involuntary muscles, similar to those of the heart, are concerned. In times of great muscular activity, when the production of heat is relatively enormous, the arterioles that supply the surface of the body are rapidly dilated so that a preponderance of blood circulates at the surface of the body, where it may readily radiate its heat into space; the vast system of perspiratory ducts, with which the skin is everywhere supplied, aiding enormously in facilitating this result, through the secretion of a film of perspiration, which in evaporating takes up large quantities of heat.

The flushed, perspiring face of a person who has violently exercised gives a familiar proof of these physiological changes; and the contrary condition, in which the peripheral circulation is restricted, and in which the pores are closed, is equally familiar. Moreover, the same cutaneous mechanism is efficient in affording the organism protection from the changes of external temperature; though the human machine, thanks to the pampering influence of civilization, requires additional protection in the form of clothing.

APPLICATIONS OF MUSCULAR ENERGY

Having thus outlined the conditions under which the muscular machine performs its work, we have now to consider briefly the external mechanisms with the aid of which muscular energy is utilized. Of course, the simplest application of this power, and the one universally employed in the animal world is that in which a direct push or pull is given to the substance, the position of which it is desired to change. We have already pointed out that there is no essential difference between pushing and pulling. The fact receives another illustration in considering the muscular mechanism. We speak of pushing when we propel something away from a body, of pulling when we draw something toward it, yet, as we have just seen, each can be accomplished merely through the contraction of a set of muscles, acting on differently disposed levers. All the bodily activities are reducible to such muscular contractions, and the diversified movements in which the organism constantly indulges are merely due to the large number and elaborate arrangement of the bony levers upon which these muscles are operated.

We may well suppose that the primitive man continued for a long period of time to perform all such labors as he undertook without the aid of any artificial mechanism; that is to say, without having learned to gain any power beyond that which the natural levers of his body provided. A brief observation of the actions of a man performing any piece of manual labor will, however, quickly demonstrate how ingeniously the bodily levers are employed, and how by shifting positions the worker unconsciously makes the most of a given expenditure of energy. By bending the arms and bringing them close to the body, he is able to shorten his levers so that he can lift a much greater weight than he could possibly raise with the arms extended. On the other hand, with the extended arm he can strike a much more powerful blow than with the shorter lever of the flexed arm. But however ingenious the manipulation of the natural levers, a full utilization of muscular energy is possible only when they are supplemented with artificial aids, which constitute primitive pieces of machinery.

These aids are chiefly of three types, namely, inclined planes, friction reducers, and levers. The use of the inclined plane was very early discovered and put into practise in chipped implements, which took the form of the wedge, in such modifications as axes, knives, and spears of metal. All of these implements, it will be observed, consist essentially of inclined planes, adapted for piercing relatively soft tissues of wood or flesh, and hence serving purposes of the greatest practical utility.

The knife-blade is an extremely thin wedge, to be utilized by force of pushing, without any great aid from acquired momentum. The hatchet, on the other hand—and its modification the axe—has its blunter blade fastened to a handle; that the principle of the wedge may be utilized at the long end of a lever and with the momentum of a swinging blow. Ages before anyone could have explained the principle involved in such obscuring terms as that, the implement itself was in use for the same purpose to which it is still applied. Indeed, there is probably no other implement that has played a larger part in the history of human industry. Even in the Rough Stone Age it was in full favor, and the earliest metallurgists produced it in bronze and then in iron. The blade of to-day is made of the best tempered steel, and the handle or helve of hickory is given a slight curve that is an improvement on the straight handle formerly employed; but on the whole it may be said that the axe is a surviving primitive implement that has held its own and demonstrated its utility in every generation since the dawn, not of history only, but of barbarism, perhaps even of savagery.

The saw, consisting essentially of a thin elongated blade, one ragged or toothed edge, is a scarcely less primitive and an equally useful and familiar application of the principle of the inclined plane—though it requires a moment's reflection to see the manner of application. Each tooth, however minute, is an inclined plane, calculated to slide over the tissue of wood or stone or iron even, yet to tear at the tissue with its point, and, with the power of numbers, ultimately wear it away.

THE WHEEL AND AXLE

The primitive friction reducer, which continues in use to the present day unmodified in principle, is the wheel revolving on an axle. Doubtless man had reached a very high state of barbarism before he invented such a wheel. The American Indian, for example, knew no better method than to carry his heavy burdens on his shoulders, or drag them along the ground, with at most a pair of parallel poles or runners to modify the friction; every move representing a very wasteful expenditure of energy. But the pre-historic man of the old world had made the wonderful discovery that a wheel revolving on an axle vastly reduces the friction between a weight and the earth, and thus enables a man or a woman to convey a load that would be far beyond his or her unaided powers. It is well to use both genders in this illustration, since among primitive peoples it is usually the woman who is the bearer of burdens. And indeed to this day one may see the women of Italy and Germany bearing large burdens on their backs and heads, and dragging carts about the streets, quite after the primitive method.

The more one considers the mechanism, the more one must marvel at the ingenuity of the pre-historic man who invented the wheel and axle. Its utility is sufficiently obvious once the thing has been done. In point of fact, it so enormously reduces the friction that a man may convey ten times the burden with its aid that he can without it. But how was the primitive man, with his small knowledge of mechanics, to predict such a result? In point of fact, of course, he made no such prediction. Doubtless his attention was first called to the utility of rolling bodies by a chance observation of dragging a burden along a pebbly beach, or over rolling stones. The observation of logs or round stones rolling down a hill might also have stimulated the imagination of some inventive genius.

A BELGIAN MILK-WAGON.

In many of the countries of Europe the dog plays an important part as a beast of burden. Stringent laws are enforced in these countries to prevent possible abuse or neglect of the animals.

Probably logs placed beneath heavy weights, such as are still employed sometimes in moving houses, were utilized now and again for many generations before the idea of a narrow section of a log adjusted on an axis was evolved. But be that as it may, this idea was put into practise before the historic period begins, and we find the earliest civilized races of which we have record—those, namely, of Old Egypt and of Old Babylonia—in full possession of the principle of the wheel as applied to vehicles. Modern mechanics have, of course, improved the mechanism as regards details, but the wheels depicted in Old Egyptian and Babylonian inscriptions are curiously similar to the most modern types. Indeed, the wheel is a striking illustration of a mechanism which continued century after century to serve the purposes of the practical worker, with seemingly no prospect of displacement.

MODIFIED LEVERS

For the rest, the mechanisms which primitive man learned early to use in adding to his working efficiency, and which are still used by the hand laborer, are virtually all modifications of our familiar type-implement, the lever. A moment's reflection will show that the diversified purposes of the crowbar, hoe, shovel, hammer, drill, chisel, are all accomplished with the aid of the same principles. The crowbar, for example, enables man to regain the power which he lost when his members were adapted to locomotion. His hands, left to themselves, as we have already pointed out, give but inadequate expression to the power of his muscles. But by grasping the long end of such a lever as the crowbar, he is enabled to utilize his entire weight in addition to his muscular strength, and, with the aid of this lever, to lift many times his weight.

The hoe, on the other hand, becomes virtually a lengthened arm, enabling a very slight muscular motion to be transformed into the long sweep of the implement, so that with small expenditure of energy the desired work is accomplished. Similarly, the sledge and the axe lengthen out the lever of the arms, so that great momentum is readily acquired, and with the aid of inertia a relatively enormous force can be applied. It will be observed that a laborer in raising a heavy sledge brings the head of the implement near his body, thus shortening the leverage and gaining power at the expense of speed; but extends his arms to their full length as the sledge falls, having now the aid of gravitation, to gain the full advantage of the long arm of the lever in acquiring momentum.

Even such elaborately modified implements as the treadmill and the rowboat are operated on the principle of the lever. These also are mechanisms that have come down to us from a high antiquity. Their utility, however, has been greatly decreased in modern times, by the substitution of more elaborate and economical mechanisms for accomplishing their respective purposes. The treadmill, indeed—which might be likened to an overshot waterwheel in which the human foot supplied the place of the falling water in giving power—has become obsolete, though a modification of it, to be driven by animal power, is still sometimes used, as we shall see in a moment.

All these are illustrations of mechanisms with the aid of which human labor is made effective. They show the devices by which primitive man used his ingenuity in making his muscular system a more effective machine for the performance of work. But perhaps the most ingenious feat of all which our primitive ancestor accomplished was in learning to utilize the muscular energy of other animals. Of course the example was always before him in the observed activity of the animals on every side. Nevertheless, it was doubtless long before the idea suggested itself, and probably longer still before it was put into practise, of utilizing this almost inexhaustible natural supply of working energy.

DOMESTICATED ANIMALS

The first animal domesticated is believed to have been the dog, and this animal is still used, as everyone knows, as a beast of burden in the far North, and in some European cities, particularly in those of Germany. Subsequently the ox was domesticated, but it is probable that for a vast period of time it was used for food purposes, rather than as a beast of burden. And lastly the horse, the worker par excellence, was made captive by some Asiatic tribes having the genius of invention, and in due course this fleetest of carriers and most efficient of draught animals was introduced into all civilized nations.

Doubtless for a long time the energy of the horse was utilized in an uneconomical way, through binding the burden on its back, or causing it to drag the burden along the ground. But this is inferential, since, as we have seen, the wheel was invented in pre-historic times, and at the dawn of history we find the Babylonians driving harnessed horses attached to wheeled vehicles. From that day to this the method of using horse-power has not greatly changed. The vast majority of the many millions of horses that are employed every day in helping on the world's work, use their strength without gain or loss through leverage, and with only the aid of rolling friction to increase their capacity as beasts of burden.

To a certain extent horse-power is still used with the aid of the modified treadmill just referred to—consisting essentially of an inclined plane of flexible mechanism made into an endless platform, which the horse causes to revolve as he goes through the movements of walking upon it. In agricultural districts this form of power is still sometimes used to run threshing machines, cider mills, wood-saws, and the like. Another application of horse-power to the same ends is accomplished through harnessing a horse to a long lever like the spoke of a wheel, fastened to an axis, which is made to revolve as the horse walks about it. Several horses are sometimes hitched to such a mechanism, which becomes then a wheel of several spokes. But this mechanism, which was common enough in agricultural districts two or three decades ago, has been practically superseded in recent years by the perambulatory steam engine.

TWO APPARATUSES FOR THE UTILIZATION OF ANIMAL POWER.

The upper figure shows the type of portable horse-power machine used for threshing grain in 1851. The lower figure is an inclined-plane horse-gear. The horse stands on the sloping platform tied to the bar in front, so that it is compelled to walk as the platform recedes.

It is obvious that the amount of work which a horse can accomplish must vary greatly with the size and quality of the horse, and with the particular method by which its energy is applied. For the purposes of comparison, however, an arbitrary amount of work has been fixed upon as constituting what is called a horse-power. This amount is the equivalent of raising thirty-three thousand pounds of weight to the height of one foot in one minute. It would be hard to say just why this particular standard was fixed upon, since it certainly represents more than the average capacity of a horse. It is, however, a standard which long usage (it was first suggested by Watt, of steam-engine fame) has rendered convenient, and one which the machinist refers to constantly in speaking of the efficiency of the various types of artificial machines. All questions of the exact legitimacy of this particular standard aside, it was highly appropriate that the labor of the horse, which has made up so large a share of the labor of the past, and which is still so extensively utilized, should continue to be taken as the measuring standard of the world's work.

[IV]

THE WORK OF AIR AND WATER

The store of energy contained in the atmosphere and in the waters of the globe is inexhaustible. Its amount is beyond all calculation; or if it were vaguely calculated the figures would be quite incomprehensible from their very magnitude. It is not, however, an altogether simple matter to make this energy available for the purposes of useful work. We find that throughout antiquity comparatively little use was made of either wind or water in their application to machinery.

Doubtless the earliest use of air as a motive power was through the application of sails to boats. We know that the Phœnicians used a simple form of sail, and no doubt their example was followed by all the maritime peoples of subsequent periods. But the use of the sail even by the Phœnicians was as a comparatively unimportant accessory to the galaxies of oars, which formed the chief motive power. The elaboration of sails of various types, adequate in extent to propel large ships, and capable of being adjusted so as to take advantage of winds blowing from almost any quarter, was a development of the Middle Ages.

The possibilities of work with the aid of running water were also but little understood by the ancients. In the days of slave labor it was scarcely worth while to tax man's ingenuity to invent machines, since so efficient a one was provided by nature. Yet the properties of both air and water were studied by various mechanical philosophers, at the head of whom were Archimedes, whose work has already been referred to, and the famous Alexandrian, Ctesibius, whose investigations became familiar through the publications of his pupil, Hero.

Perhaps the most remarkable device invented by Ctesibius was a fire-engine, consisting of an arrangement of valves constituting a pump, and operating on the principle which is still in vogue. It is known, however, that the Egyptians of a much earlier period used buckets having valves in their bottoms, and these perhaps furnished the foundation for the idea of Ctesibius. It is unnecessary to give details of this fire-engine. It may be noted, however, that the principle of the lever is the one employed in its operation to gain power. A valve consists essentially of any simple hinged substance, arranged so that it may rise or fall, alternately opening and closing an aperture. A mere flap of leather, nailed on one edge, serves as a tolerably effective valve. At least one of the valves used by Ctesibius was a hinged piece of smooth metal. A piston fitted in a cylinder supplies suction when the lever is raised, and pressure when it is compressed, alternately opening the valve and closing the valve through which the water enters the tube. Meantime a second valve alternating with the first permits the water to enter the chamber containing air, which through its elasticity and pressure equalizes the force of the stream that is ejected from the chamber through the hose.

SUCTION AND PRESSURE

In the construction of this and various other apparatus, Ctesibius and Hero were led to make careful studies of the phenomena of suction. But in this they were not alone, since numerous of their predecessors had studied the subject, and such an apparatus as the surgeon's cupping glass was familiarly known several centuries before the Christian era. The cupping glass, as perhaps should be explained to the reader of the present day—since the apparatus went out of vogue in ordinary medical practise two or three generations ago—consists of a glass cup in which the air is exhausted, so as to suck blood from any part of the surface of a body to which it is applied. Hero describes a method of exhausting air by which such suction may be facilitated. But neither he nor any other philosopher of his period at all understood the real nature of this suction, notwithstanding their perfect familiarity with numerous of its phenomena. It was known, for example, that when a tube closed at one end is filled with water and inverted with the open end beneath the surface of the water, the water remains in the tube, although one might naturally expect that it would obey the impulses of gravitation and run out, leaving the tube empty. A familiar explanation of this and allied phenomena throughout antiquity was found in the saying that "Nature abhors a vacuum." This explanation, which of course amounts to no explanation at all, is fairly illustrative of the method of metaphysical word-juggling that served so largely among the earlier philosophers in explanation of the mysteries of physical science.

The real explanation of the phenomena of suction was not arrived at until the revival of learning in the seventeenth century. Then Torricelli, the pupil of Galileo, demonstrated that the word suction, as commonly applied, had no proper application; and that the phenomena hitherto ascribed to it were really due to the pressure of the atmosphere. A vacuum is merely an enclosed space deprived of air, and the "abhorrence" that Nature shows to such a space is due to the fact that air has weight and presses in every direction, and hence tends to invade every space to which it can gain access. It was presently discovered that if the inverted tube in which the water stands was made high enough, the water will no longer fill it, but will sink to a certain level. The height at which it will stand is about thirty feet; above that height a vacuum will be formed, which, for some reason, Nature seems not to abhor. The reason is that the weight of any given column of water about thirty feet in height is just balanced by the weight of a corresponding column of atmosphere. The experiments that gave the proof of this were made by the famous Englishman, Boyle. He showed that if the heavy liquid, mercury, is used in place of water, then the suspended column will be only about thirty inches in height. The weight or pressure of the atmosphere at sea level, as measured by these experiments, is about fifteen pounds to the square inch.

Boyle's further experiments with the air and with other gases developed the fact that the pressure exerted by any given quantity of gas is proportional to the external pressure to which it is subjected, which, after all, is only a special application of the law that action and reaction are equal. The further fact was developed that under pressure a gas decreases at a fixed rate in bulk. A general law, expressing these facts in the phrase that density and elasticity vary inversely with the pressure in a precise ratio, was developed by Boyle and the Frenchman, Mariotte, independently, and bears the name of both of its discoverers. No immediate application of the law to the practical purposes of the worker was made, however, and it is only in recent years that compressed air has been extensively employed as a motive power. Even now it has not proved a great commercial success, because other more economical methods of power production are available. In particular cases, however, it has a certain utility, as a relatively large available source of energy may be condensed into a very small receptacle.

A very striking experiment illustrating the pressure of the air was made by a famous contemporary of Boyle and Mariotte, by the name of Otto von Guericke. He connected an air pump with a large brass sphere, composed of two hemispheres, the edges of which fitted smoothly, but were not connected by any mechanism. Under ordinary conditions the hemispheres would fall apart readily, but von Guericke proved, by a famous public demonstration, that when the air was exhausted in the sphere, teams of horses pulling in opposite directions on the hemispheres could not separate them. This is famous as the experiment of the Magdeburg spheres, and it is often repeated on a smaller scale in the modern physical laboratory, to the astonishment of the tyro in physical experiments.

The first question that usually comes to the mind of anyone who has personally witnessed such an experiment, is the question as to how the human body can withstand the tremendous force to which it is subjected by an atmosphere exerting a pressure of fifteen pounds on every square inch of its surface. The explanation is found in the uniform distribution of the pressure, the influence of which is thus counteracted, and by the fact that the tissues themselves contain everywhere a certain amount of air at the same pressure. The familiar experiment of holding the hand over an exhausted glass cylinder—which experiment is indeed but a modification of the use of the cupping glass above referred to—illustrates very forcibly the insupportable difficulties which the human body would encounter were not its entire surface uniformly subjected to the atmospheric pressure.

AIR IN MOTION

At about the time when the scientific experiments with the pressure of gases were being made, practical studies of the effects of masses of air in motion were undertaken by the Dutch philosopher, Servinus. The use of the windmill in Holland as a means of generating power doubtless suggested to Servinus the possibility of attaching a sail to a land vehicle. He made the experiment, and in the year 1600 constructed a sailing car which, propelled by the wind, traversed the land to a considerable distance, on one occasion conveying a company of which Prince Maurice of Orange was a member. But his experiments have seldom been repeated, and indeed their lack of practical feasibility scarcely needs demonstration.

The utility of the wind, however, in generating the power in a stationary mechanism is familiar to everyone. Windmills were constructed at a comparatively early period, and notwithstanding all the recent progress in the development of steam and electrical power, this relatively primitive so-called prime mover still holds its own in agricultural districts, particularly in its application to pumps. A windmill consists of a series of inclined planes, each of which forms one of the radii of a circle, or spokes of a wheel, to the axle of which a gearing is adjusted by which the power generated is utilized. The wheel is made to face the wind by the wind itself blowing against a sort of rudder which projects from the axis. The wind blowing against the inclined surfaces or vanes of the wheel causes each vane to move in accordance with the law of component forces, thus revolving the wheel as a whole.

WINDMILLS OF ANCIENT AND MODERN TYPES.

The smaller figures show Dutch windmills of the present day, many of which are identical in structure with the windmills of the middle ages. It will be seen that the sails can be furled when desired to put the mill out of operation. In the mill of modern type (large figure) the same effect is produced by slanting the slats of the wheel.

It has been affirmed that the Romans had windmills, but "the silence of Vitruvius, Seneca, and Chrysostom, who have spoken of the advantages of the wind, makes this opinion questionable." It has been supposed by other writers that windmills were used in France in the sixth century, while still others have maintained that this mechanism was unknown in Europe until the time of the Crusades. All that is tolerably certain is that in the twelfth century windmills were in use in France and England. It is recorded that when they began to be somewhat common Pope Celestine III. determined that the tithes of them belonged to the clergy.

INHERENT DEFECTS OF THE WINDMILL

The mediæval European windmill was supplied with great sails of cloth, and its picturesque appearance has been made familiar to everyone through the famous tale of Don Quixote. The modern windmill, acting on precisely the same principle, is a comparatively small affair, comprising many vanes of metal, and constituting a far more practical machine. The great defect of all windmills, however, is found in the fact that of necessity they furnish such variable power, since the force of the wind is incessantly changing. Worst of all, there may be protracted periods of atmospheric calm, during which, of course, the windmill ceases to have any utility whatever. This uneradicable defect relegates the windmill to a subordinate place among prime movers, yet on the other hand, its cheapness insures its employment for a long time to come, and the industry of manufacturing windmills continues to be an important one, particularly in the United States.

RUNNING WATER

The aggregate amount of work accomplished with the aid of the wind is but trifling, compared with that which is accomplished with the aid of water. The supply of water is practically inexhaustible, and this fluid being much more manageable than air, can be made a far more dependable aid to the worker. Every stream, whatever its rate of flow, represents an enormous store of potential energy. A cubic foot of water weighs about sixty-two and a half pounds. The working capacity of any mass of water is represented by one-half its weight into the square of its velocity; or, stated otherwise, by its weight into the distance of its fall. Now, since the interiors of the continents, where rivers find their sources, are often elevated by some hundreds or even thousands of feet, it follows that the working energy expended—and for the most part wasted—by the aggregate water current of the world is beyond all calculation. Meantime, however, a portion of the energy which in the aggregate represents an enormous working power is utilized with the aid of various types of water wheels.

Watermills appear to have been introduced in the time of Mithridates, Julius Cæsar, and Cicero. Strabo informs us that there was a watermill near the residence of Mithridates; and we learn from Pomponius Sabinus, that the first mill seen at Rome was erected on the Tiber, a little before the time of Augustus. That they existed in the time of Augustus is obvious from the description given of them by Vitruvius, and the epigram of Antipater, who is supposed to have lived in the time of Cicero. But though mills driven by water were introduced at this early period, yet public mills did not appear till the time of Honorius and Arcadius. They were erected on three canals, which conveyed water to the city, and the greater number of them lay under Mount Janiculum. When the Goths besieged Rome in 536, and stopped the large aqueduct and consequently the mills, Belisarius appears to have constructed, for the first time, floating mills upon the Tiber. Mills driven by the tide existed at Venice in the year 1046, or at least in 1078.

The older types of water wheel are exceedingly simple in construction, consisting merely of vertical wheels revolving on horizontal axes, and so placed as to receive the weight or pressure of the water on paddles or buckets at their circumference. The water might be allowed to rush under the wheel, thus constituting an under-shot wheel; or more commonly it flows from above, constituting an over-shot wheel. Where the natural fall is not available, dams are employed to supply an artificial fall.

This primitive type of water wheel has been practically abandoned within the last generation, its place having been taken by the much more efficient type of wheel known as the turbine. This consists of a wheel, usually adjusted on a vertical axis, and acting on what is virtually the principle of a windmill. To gain a mental picture of the turbine in its simplest form, one might imagine the propelling screw of a steamship, placed horizontally in a tube, so that the water could rush against its blades. The tiny windmills which children often make by twisting pieces of paper illustrate the same principle. Of course, in its developed form the turbine is somewhat elaborated, in the aim to utilize as large a proportion of the energy of the falling water as is possible; but the principle remains the same.

The turbine wheel was invented by a Frenchman named Fourneyron, about three-quarters of a century ago (1827), but its great popularity, in America in particular, is a matter of the last twenty or thirty years. To-day it has virtually supplanted every other type of water wheel. To use any other is indeed a wasteful extravagance, as the perfected turbine makes available more than eighty per cent. of the kinetic energy of any mass of falling water. A turbine wheel two feet in diameter is able to do the work of an enormous wheel of the old type.

Turbine wheels are of several types, one operating in a closed tube to which air has no access, and another in an open space in the presence of air. The water may also be made to enter the turbine at the side or from below, thus serving to support the weight of the mechanism—a consideration of great importance in the case of such gigantic turbines as those that are employed at Niagara Falls, which we shall have occasion to examine in detail in a later chapter.

WATER WHEELS.

Fig. 1 shows a model of the so-called breast wheel, a familiar type of water wheel that has been in use since the time of the Romans. Figs. 2 and 3 show similar wheels as used to-day in Belgium. Fig. 4 shows a model of Fourneyron's turbine. This wheel was made in 1837, but the original turbine was introduced by Fourneyron in 1827. The turbine wheel has now almost supplanted the other forms of water wheel except in rural districts.

The power generated by a revolution of the turbine wheel may, of course, be utilized directly by belts or gearings attached to its axle, or it may be transferred to a distance, with the aid of a dynamo generating electricity. The latter possibility, which has only recently been developed, and which we shall have occasion to examine in detail in connection with our studies of the power at Niagara, gives a new field of usefulness to the turbine wheel, and makes it probable that this form of power will be vastly more used in the future than it has been in the past. Indeed, it would not be surprising were it ultimately to become the prime source of working energy as utilized in every department of the world's work.

Mr. Edward H. Sanborn, in an article on Motive Power Appliances in the Twelfth Census Report of the United States, comments upon the recent advances in the use of water wheels as follows:

"One notable advance in turbine construction has been the production of a type of wheel especially designed for operating under much higher heads of water than were formerly considered feasible for wheels of this type. Turbines are now built for heads ranging from 100 to 1,200 feet, and quite a number of wheels are in operation under heads of from 100 to 200 feet. This is an encroachment upon the field occupied almost exclusively by wheels variously known as the 'impulse,' 'impact,' 'tangential,' or 'jet' type, the principle of which is the impact of a powerful jet of water from a small nozzle upon a series of buckets mounted upon the periphery of a small wheel."

"The impact water wheel," Mr. Sanborn continues, "has come largely into use during the last ten years, principally in the far West, where higher heads of water are available than can be found in other parts of the country. With wheels of this type, exceedingly simple in construction and of comparatively small cost, a large amount of power is developed with great economy under the great heads that are available. With the tremendous water pressure developed by heads of 1,000 feet and upward, which in many cases are used for this purpose, wheels of small diameter develop an extraordinary amount of power. To the original type of impact wheel which first led the field have been added several styles embodying practically the same principle. Considerable study has been given to the designing of buckets with a view to securing free discharge and the avoidance of any disturbing eddies, and important improvements have resulted from the thorough investigation of the action of the water during, and subsequent to, its impact on the buckets. The impact wheel has been adapted to a wide range of service with great variation as to the conditions under which it operates, wheels having been made in California from 30 inches to 30 feet in diameter, and to work under heads ranging from 35 to 2,100 feet, and at speeds ranging from 65 to 1,100 revolutions per minute. A number of wheels of this type have been built with capacities of not less than 1,000 horse-power each."

HYDRAULIC POWER

A few words should be said about the familiar method of transmitting power with the aid of water, as illustrated by the hydrostatic press. This does not indeed utilize the energy of the water itself, but it enables the worker to transmit energy supplied from without, and to gain an indefinite power to move weights through a short distance, with the expenditure of very little working energy. The principle on which the hydrostatic press is based is the one which was familiar to the ancient philosophers under the name of the hydrostatic paradox. It was observed that if a tube is connected with a closed receptacle, such as a strong cask, and cask and tube are filled with water, the cask will presently be burst by the pressure of the water, provided the tube is raised to a height, even though the actual weight of water in the tube be comparatively slight. A powerful cask, for example, may be burst by the water poured into a slender pipe. The result seems indeed paradoxical, and for a long time no explanation of it was forthcoming. It remained for Servinus, whose horseless wagon is elsewhere noticed, to discover that the water at any given level presses equally in all directions, and that its pressure is proportionate to its depth, quite regardless of its bulk. Then, supposing the tube in our experiment to have a cross-section of one square inch, a pressure equal to that in the tube would be transmitted to each square inch of the surface of the cask; and the pressure might thus become enormous.

If, instead of a tube lifted to a height, the same tube is connected with a force pump operated with a lever—an apparatus similar to the fire-engine of Ctesibius—it is obvious that precisely the same effect may be produced; whatever pressure is developed in the piston of the force pump, similar pressure will be transferred to a corresponding area in the surface of the cask or receptacle with which the force pump connects. In practise this principle is utilized, where great pressure is desired, by making a receptacle with an enormous piston connecting with the force pump just described.

An indefinite power may thus be developed, the apparatus constituting virtually a gigantic lever. But the principle of the equivalence of weight and distance still holds, precisely as in an actual lever, and while the pressure that may be exerted with slight expenditure of energy is enormous, the distance through which this pressure acts is correspondingly small. If, for example, the piston of the force pump has an area of one square inch, while the piston of the press has an area of several square feet, the pressure exerted will be measured in tons, but the distance through which it is exerted will be almost infinitesimal. The range of utility of the hydrostatic press is, therefore, limited, but within its sphere, it is an incomparable transmitter of energy.

HYDRAULIC PRESS AND HYDRAULIC CAPSTAN.

The upper figure shows Bramah's original hydraulic pump and press, now preserved in the South Kensington Museum, London. The machine was constructed in 1796 by Joseph Bramah to demonstrate the principle of his hydraulic press. The discrepancy in size between the small lever worked by hand and the enormous lever carrying a heavy weight gives a vivid impression of the gain in power through the use of the apparatus. The lower figure shows the hydraulic capstan used on many modern ships, in which the same principle is utilized.

Moreover, it is possible to reverse the action of the hydraulic apparatus so as to gain motion at the expense of power. A familiar type of elevator is a case in point. The essential feature of the hydraulic elevator consists of a ram attached to the bottom of the elevator and extending down into a cylinder, slightly longer than the height to which the elevator is to rise. The ram is fitting into a cylinder with water-tight packing, or a cut leather valve. Water under high pressure is admitted to the cylinder through the valve at the bottom, and the pressure thus supplied pushes up the ram, carrying the elevator with it, of course. Another valve allows the water to escape, so that ram and elevator may descend, too rapid descent being prevented by the partial balancing of ram and elevator with weights acting over pulleys. The ram, to the end of which pressure is thus applied, need be but a few inches in diameter. Water pressure is secured by bringing water from an elevation. Such an elevator acts slowly, but is a very safe and in many ways satisfactory mechanism. Such elevators are still used extensively in Europe, but have been almost altogether displaced in America by the electric elevator.