Nature's Teachings: Human Invention Anticipated by Nature

by J. G. Wood

The Boat.

There is no doubt that the first idea of locomotion in the water, independently of swimming, was the raft; nor is it difficult to trace the gradual development of the raft into a Boat. The development of the Kruman’s canoe into the Great Eastern, or a modern ironclad vessel, is simply a matter of time.

It is tolerably evident that the first raft was nothing more than a tree-trunk. Finding that the single trunk was apt to turn over with the weight of the occupant, the next move was evidently to lash two trunks side by side.

Next would come the great advance of putting the trunks at some distance apart, and connecting them with cross-bars. This plan would obviate even the chance of the upsetting of the raft, and it still survives in that curious mixture of the raft and canoe, the outrigger boat of the Polynesians, which no gale of wind can upset. It may be torn to pieces by the storm, but nothing can capsize it as long as it holds together.

Laying a number of smaller logs or branches upon the bars which connect the larger logs is an evident mode of forming a continuous platform, and thus the raft is completed. It would not be long before the superior buoyancy of a hollow over a solid log would be discovered, and so, when the savage could not find a log ready hollowed to his hand, he would hollow one for himself, mostly using fire in lieu of tools. The progress from a hollowed log, or “dug-out,” as it is popularly called, to the bark canoe, and then the built boat, naturally followed, the boats increasing in size until they were developed into ships.

Such, then, is a slight sketch of the gradual construction of the Boat, based, though perhaps ignorantly, on the theory of displacement. Now, let us ask ourselves whether, in creation, there are any natural boats which existed before man came upon the earth, and from which he might have taken the idea if he had been able to reason on the subject. The Paper Nautilus is, of course, the first example that comes before the mind; but although, as we have seen, the delicate shell of the nautilus is not used as a boat, and its sailing and rowing powers are alike fabulous, there is, as is the case with most fables, a substratum of truth, and there are aquatic molluscs which form themselves into boats, although they do not propel themselves with sails or oars.

Many species of molluscs possess this art, but we will select one as an example of them all, because it is very plentiful in our own country, and may be found in almost any number. It is the common Water-snail (Limnæa stagnalis), which abounds in our streams where the current is not very strong. Even in tolerably swift streams the Limnæa may be found plentifully in any bay or sudden curve where a reverse current is generated, and therefore the force of the stream is partially neutralised. These molluscs absolutely swarm in the Cherwell, and in the multitudinous ditches which drain the flat country about Oxford into that river as well as the Isis.

Belonging to the Gasteropods, the Water-snail can crawl over the stones or aquatic vegetation, just as the common garden snail or slug does on land. But it has another mode of progression, which it very often employs in warm weather. It ascends to the surface of the water, reverses its position so that the shell is downward, spreads out the foot as widely as possible, and then contracts it in the centre, so as to form it into a shallow boat.

The carrying capacity of this boat is necessarily small, but as the shell and nearly the whole of the animal are submerged, and therefore mostly sustained by the water, a very small amount of flotative power is sufficient for the purpose. Sometimes, on a fine day, whole fleets of these natural boats may be seen floating down the stream, thus obtaining a change of locality without any personal exertion.

In perfectly still water, where no current can waft the Limnæa on its easy voyage, it still is able to convey itself from one place to another. By means of extending and contracting the foot, it actually contrives to crawl along the surface of the water almost as readily as if it were upon the under side of some solid body, and, although its progress is slow, it is very steady. Another very common British water-snail, the Pouch-shell (Physa fontinalis), has almost exactly the same habits. Reference will be made to the Pouch-shell on another page.

The capacity for converting the body into a boat is not confined to the molluscs, but is shared by many other animals. Take, for example, the well-known marine animals, called popularly Sea-anemones. As they appear when planted on the rocks, they look as incapable of motion as the flowers whose names they bear. Yet, by means of the flattened base, which they use just as a snail uses its feet, they can manage to glide along the rocks in any direction, though very slowly.

The base is capable of extension and contraction, and by elongating one side of it, fixing the elongated portion, and then raising the remainder of the base towards it, the animal makes practically a series of very slow steps. This mode of progression may often be seen in operation on the glass front of an aquarium.

The same property of expansion and contraction enables the Sea-anemones to convert their bodies into boats, and float on the surface of the water. When one of these animals wishes to swim, it ascends the object to which it is clinging—say the glass of the aquarium—until it has reached the air. It then very slowly, and bit by bit, detaches the upper part of the base from the glass, allowing itself to hang with its tentacles downward. These, by the way, are almost wholly withdrawn when the animal is engaged in this business. By degrees the whole of the base is detached from the glass except a very tiny portion of the edge. The base is next contracted in the middle into the form of a shallow cup, and, when this is done, the last hold of the glass is released, and the animal floats away, supported by its hollowed base.

Entomologists are familiar with the following facts, and were this work addressed to them alone, a simple mention of the insect would be sufficient. But as this work is intended for the general public, it will be necessary to give a description, though a brief one, of the wonderful manner in which an insect, which we are apt to think is only too common, plays the part of a boat at its entrance to life and just before its departure from this world, not to mention its intermediate state, to which reference will be made under another heading.

The insect in question is the common Gnat (Culex pipiens), which makes such ravages upon those who are afflicted, like myself, with delicate skins, and can have a limb rendered useless for days by a single gnat-bite.

In this insect, the beginning and the end of life are so closely interwoven, that it is not easy to determine which has the prior claim to description, but we will begin with the egg.

With very few exceptions, such as the Earwig, which watches over its eggs and young like a hen over her nest and chickens, the insects merely deposit their eggs upon or close to the food of the future young, and leave them to their fate. The eggs of the Gnat, however, require different treatment. The young larvæ, when hatched, immediately pass into the water in which they have to live, and yet the eggs are so constituted that they need the warmth of the sun in order to hatch them. The machinery by which both these objects are attained is singularly beautiful.

The shape of the egg very much resembles that of a common ninepin, and the structure is such that it must be kept upright, so that the top shall be exposed to the air and sun, and the bottom be immersed in the water. It would be almost impossible that these conditions should be attained if the eggs were either dropped separately into the water or fixed to aquatic plants, as is the case with many creatures whose eggs are hatched solely in or on the water.

As is the case with many insects, each egg when laid is enveloped with a slight coating of a glutinous character, so that they adhere together. And, in the case of the Gnat, this material is insoluble in water, and hardens almost immediately after the egg is deposited. Taking advantage of these peculiarities, the female Gnat places herself on the edge of a floating leaf or similar object, so that her long and slender hind-legs rest on the water. In some mysterious way, the eggs, as they are successively produced, are passed along the hind-legs, and are arranged side by side in such a manner that they are formed into the figure of a boat, being fixed to each other by the glutinous substance which has already been mentioned.

It is a very remarkable fact, which assists in strengthening the theory on which this book is written, that the lines of the best modern life-boats are almost identical with those of the Gnat-boat, and that both possess the power of righting themselves if capsized. In all trials of a new life-boat, one of the most important is that which tests her capability of self-righting; and any one who has witnessed such experiments, and has tried to upset a Gnat-boat, cannot but be struck with the singular similitude between the boat made by the hand of man and that constructed by the legs of an insect, without even the aid of eyes.

Push the Gnat-boat under water, and it shoots to the surface like a cork, righting itself as it rises. Pour water on it, and exactly the same result occurs, so that nothing can prevent it from floating. Then, when the warm air has done its work in hatching the enclosed young, a little trap-door opens at the bottom of the egg, lets the young larvæ into the water, and away they swim.

Now we come to another phase of existence in which the Gnat forms a boat. Every one knows the little active Gnat larvæ, with their large heads and slender bodies, much like tadpoles in miniature. When they have reached their full growth, and assume the pupal form, their shape is much changed. The fore part of the body is still more enlarged, as it has to contain the wings and legs, which have so great a proportion to the body of the perfect Gnat. And, instead of floating with its head downwards, and breathing through its tail as it did when a larva, it now floats with the head uppermost, and breathes through two little tubes.

Even in its former state the creature had something almost grotesque in its aspect, the head, when magnified, looking almost as like a human face as does that of a skate. But in its pupal state it looks as if it had put on a large comical mask much too large for it, very much like those paper masks which are enclosed in crackers, and have to be worn by those who draw them.

In process of time the pupa changes to a perfect Gnat within this shelly case, able to move, but unable to eat. The body shrinks in size, and the wings and legs are formed, both being pressed closely to the body. When the Gnat is fully developed, the pupal skin splits along the back, and opens out into a curiously boat-like shape, the front, which contains the heavier part of the insect, being much the largest, and consequently being able to bear the greatest weight.

By degrees, the Gnat draws itself out of the split pupal skin, resting its legs on it as fast as they are released. It then shakes out its wings to dry, and finally takes to the air.

It is a really wonderful fact that the insect which, for three stages in life—namely, an egg, larva, and pupa—lived in the water, should in the fourth not only be incapable of aquatic life, but should employ its old skin to protect it from that very element in which it was living only a minute or two before.

Should the reader wish to examine for himself either the egg or skin boat of the Gnat, he can easily procure them by searching any quiet pond, or even an uncovered water-butt. They are, of course, very small, averaging about the tenth of an inch in length, and are nearly always to be found close to the side either of pond or tub, being drawn there by the power of attraction.

I may here mention that there are other dipterous insects belonging to the genus Stratiomys, which undergo their metamorphosis in a very similar fashion. In these insects, the larva breathes through the tail, and when it attains its pupal condition, the actual insect is very much smaller than the pupal skin, only occupying the anterior and enlarged part. Indeed, the difference of size is so great, that several entomologists believed the future Stratiomys to be but a parasite on the original larva. The beautiful Chameleon-fly (Stratiomys chamæleon) is a familiar example of these insects.

NAUTICAL.
CHAPTER II.
THE OAR, THE PADDLE, AND THE SCREW.

Propulsion by the Oar.—Parallels in the Insect World.—The “Water-boatman.”—Its Boat-like Shape.—The Oar-like Legs.—Exact mechanical Analogy between the Legs of the Insect and the Oars of the human Rower.—“Feathering” Oars in Nature and Art.—The Water-boatman and the Water-beetles.—The Feet of the Swan, Goose, and other aquatic Birds.—The Cydippe, or Beroë.—The Self-feathering Paddle-wheel.—Indirect Force.—The Wedge, Screw, and Inclined Plane.—“Sculling” a Boat.—The “Tanka” Girls of China.—Mechanical Principle of the Screw, and its Adaptation to Vessels.—Gradual Development of the Nautical Screw.—Mechanical Principle of the Tail of the Fish, the Otter, and the sinuous Body of the Eel and Lampern.—The Coracle and the Whirlwig-beetle.

THE Boat naturally reminds us of the Boatman. In the two gnat-boats which have been described there is no propelling power used or needed, the little vessel floating about at random, and its only object being to keep afloat. But there are many cases where the propelling power is absolutely essential, and where its absence would mean death, as much as it would to a ship which was becalmed in mid ocean without any means of progress or escape. There are, for example, hundreds of creatures, belonging to every order of animals, which are absolutely dependent for their very existence on their power of propulsion, and I believe that there is not a single mode of aquatic progression employed by man which has not been previously carried out in the animal world. There are so many examples of this fact that I am obliged to select a very few typical instances in proof of the assertion.

Taking the Oar as the natural type of progression in the water, we have in the insect world numerous examples of the very same principle on which our modern boats are propelled. And it is worthy of notice, that the greater the improvement in rowing, the nearer do we approach the original insect model.

The first which we shall notice is the insect which, from its singular resemblance to a boat propelled by a pair of oars, has received the popular name of Water-boatman. Its scientific name is Notonecta glauca, the meaning of which we shall presently see. It belongs to the order of Heteroptera, and is one of a numerous group, all bearing some resemblance to each other in form, and being almost identical in habits. Though they can fly well, and walk tolerably, they pass the greater part of their existence in the water, in which element they find their food.

Predacious to a high degree, and armed with powerful weapons of offence, it is one of the pirates of the fresh water, and may be found in almost every pond and stream, plying its deadly vocation.

Its large and powerful wings seem only to be employed in carrying it from one piece of water to another, while its first and second pairs of legs are hardly ever used at all for progression. The last pair of legs are of very great length, and furnished at their tips with a curiously constructed fringe of stiff hairs. The body is shaped in a manner that greatly resembles a boat turned upside down, the edge of the elytra forming a sort of ridge very much like the keel of the boat.

When the creature is engaged in swimming, it turns itself on its back, so as to bring the keel downwards, and to be able to cut the water with the sharp edge. From this habit it has derived the name of Notonecta, which signifies an animal which swims on its back. The first and second pairs of legs are clasped to the body, and the last pair are stretched out as shown in the illustration, not only looking like oars, but being actually used as oars.

Now, I wish especially to call the reader’s attention to the curiously exact parallel between the water-boatman and the human oarsman. As the reader may probably know, the oar is a lever of the second order, i.e. the power comes first, then the weight, and then the fulcrum. The arm of the rower furnishes the power, the boat is the weight to be moved, and the water is the fulcrum against which the lever acts.

I have more than once heard objections to this definition, the objectors saying that the water was a yielding substance, and therefore could not be the fulcrum. This objection, however, was easily refuted by taking a boat up a narrow creek, and rowing with the oar-blades resting on the shore, and not in the water.

Now, the swimming legs of the water-boatman are exact analogues of the oars of a human rower. The internal muscles at the juncture of the leg with the body supply the place of the rower’s arms, the leg itself takes the office of the oar, and the body of the insect is the weight to be moved, and the water supplies the fulcrum. Even the broad blade at the end of the oar is anticipated by the fringe of bristles at the end of the leg, and its sharpened edge by the shape of the insect’s limb.

Besides these resemblances, there is another which is worthy of notice. All rowers know that one of their first lessons is to “feather” their oars, i.e. to turn the blade edgewise as soon as it leaves the water. Nothing looks more awkward than for a boatman to row without feathering. (We all must remember the eulogy on the “Jolly Young Waterman,” who “feathered his oars with skill and dexterity.”) In the first place, he must lift his oar very high out of the water, and, in the second, he will be impeded by any wind that happens to come against the blades.

The Water-boatman, however, does not lift its legs out of the water after every stroke, as a human boatman does, and therefore it has no need to feather in the same way. But there is even greater need for a feathering of some kind in the insect’s leg, on account of the greater resistance offered by water than by air, and this feathering is effected by the arrangement of the blade-bristles, which spread themselves against the water as the stroke is made, and collapse afterwards, so as to give as little resistance as possible when the stroke is completed.

In Art we have invented many similar contrivances, but I believe that there is not one in which we have not been anticipated by Nature. Putting aside the insect which has just been described, we have the whole tribe of water-beetles, in which the same principle is carried out in an almost identical manner. In the accompanying illustration, the oar, the rower, and the boat are placed above one another, and next to them are seen one of the oar-legs of the water-boatman and the insect as it appears when swimming on its back.

Then, there is the foot of the duck, goose, swan, and various other aquatic birds, in which the foot presents a broad blade as it strikes against the water, and a narrow edge as it recovers from the stroke. Some years ago, a steam yacht was built and propelled by feet made on the model of those of the swan. She was a very pretty vessel, but art could not equal nature, and at present the swan-foot propeller, however perfect in theory, has not succeeded in action. Perhaps, if some nautical engineer were to take it in hand, he would procure the desired result.

Almost exactly similar is the mode of propulsion employed by the lobster, the prawns and shrimps, their tails expanding widely into a fan-like shape as they strike against the water, and then collapsing when the stroke is withdrawn, so as to allow them to pass through the water with the least possible resistance.

The same principle is to be seen in the lively little Acaleph, for which there is unfortunately no popular name, and which we must therefore call by its scientific title of Cydippe, or Beroë, these names being almost indifferently used. When full grown, it is about as large as an acorn, and very much of the same shape. It is as transparent as if made of glass, and, when in the water, is only visible to practised eyes.

En passant, I may remark that the familiar term of “water,” when applied to diamonds, is owing to their appearance when placed in distilled water. Those which can be at once seen are called stones of the second water. Those which cannot be seen, because their refractive powers are equal to those of the water, are called “diamonds of the first water,” and are very much more valuable than the others.

As the Cydippe is, in fact, little more than sea-water, entangled in the slightest imaginable and most transparent tissue of animal fibre, it is evident that the water and the Cydippe must be of almost equal refracting power, and that therefore the acaleph must be as invisible as diamonds of the “first water.” Indeed, I have often had specimens in a glass jar which were absolutely invisible to persons to whom I wished to show them.

But an experienced eye detects the creature at once. Along its body, at equal distances, are eight narrow bands, over which the colours of the rainbow are, though very faint, perpetually rippling. This appearance is caused by the machinery which impels the body, and which seems never to cease. Each of these bands is composed of a vast number of tiny flaps, which move up and down in regular succession, so as to cause the light to play on their surfaces. And, as they move as if set on hinges, they of course offer no resistance to the water after their stroke is made.

Now let us compare these works of nature with those of art. We have already seen the parallels of the oar, and we now come to those of the paddle-wheel. When paddle-steamers were first invented, the blades were fixed and projected from the wheel, as if they had been continuations of its spokes. It was found, however, that a great waste of power, together with much inconvenience, was caused by this arrangement. Not only was a considerable weight of water raised by each blade after it passed the middle of its stroke, but the steam power was given nearly as much to lifting and shaking the vessel as to propulsion.

A new kind of paddle-wheel was then invented, in which the blades were ingeniously jointed to the wheel, so that they presented their flat surfaces to the water while propelling, and their edges when the stroke was over. This, which is known by the name of the “Self-feathering Paddle-wheel,” was thought to be a very clever invention, and so it was; but not even the inventors were likely to have known that if they had only looked into the book of Nature, they might have found plenty of self-feathering paddle-wheels, beside the few which my limited space enables me to give.

If the reader will look at the illustration, he will see that on one side is represented the self-feathering paddle-wheel of Art, with its ingenious arrangement of rods and hinges. On the other side there comes, first, the common Prawn, shown with its tail expanded in the middle of its stroke.

Just below it is a Cydippe of its ordinary size, showing the paddle-bands, one of which is drawn at the side much magnified, so as to show the arrangement of the little paddles. As to the tentacles which trail from the body, we shall treat of them when we come to our next division of the subject of the work.

Lastly, there is a representation of the self-feathering feet of the Duck, the left foot expanded in striking the water, and the right closed so as to offer no resistance when drawn forward for another stroke. The swan’s foot shows this action even more beautifully than does that of the duck.

We now come to another mode of propulsion, namely, that which is not due to direct pressure of a more or less flat body against the water, but to the indirect principle of the screw, wedge, or inclined plane.

Space being valuable, I will only take two instances, namely, the well-known mode of propelling a boat by a single oar working in a groove or rowlock in the middle of the stern, and the ordinary screw of modern steamers.

Most of my readers must have seen a sailor in the act of “sculling” a boat. A tolerably deep notch is sunk in the centre of the stern, and the oar is laid in it, as shown in the central illustration, on the right-hand side. The sailor then takes the handle of the oar, and works it regularly backwards and forwards, without taking the blade out of the water. The boat at once begins to move forward, and, when the oar is urged by a strong and experienced man, can be propelled with wonderful speed. The well-known “Tanka” boat-girls of China never think of using two oars, a single oar in the stern being all-sufficient for the rapid and intricate evolutions required in their business.

The mechanical process which is here employed is nothing more than that of the inclined plane, or rather, the wedge, the oar-blade forming the wedge, and the force being directed against the stern of the boat, and so driving it through the water.

The Rudder affords another example of a similar force, although it is used more for directing than propelling a vessel. Still, just as the scull is used not only for propelling, but for steering the boat, the rudder, when moved steadily backwards and forwards, can be used for propulsion as well as steerage. In the absence of oars, this property is most useful, as I can practically testify.

So different in appearance are the screw and the inclined plane, that very few people would realise the fact that the screw is nothing but an inclined plane wound round a cylinder, or rather, is a circular inclined plane. The ordinary corkscrew is a good example of this principle, the cylinder being but an imaginary one.

Now, if the screw be turned round, it is evident that force is applied just on the principle of the wedge, and this principle is well shown in the various screw-presses, of which the common linen-press is a familiar example, as was the original printing-press, which still survives as a toy for children.

We all know the enormous force exerted by screws when working in wood, and how, when the screw-driver is turned in the reverse direction, the instrument is forced backwards, though the operator is leaning against it with all his weight. In fact, a comparatively small screw, if working in hard wood or metal, so that the threads could not break, could lift a heavy man.

Substitute water for wood or metal, and the result would be the same in principle, though the resistance would be less. As the loss of power by friction would prevent a large vessel from being propelled by a stern oar moved like a scull, the idea was invented of applying the same kind of power by a large screw, which should project into the water from the stern of the vessel. This modification, moreover, would have the advantage of forcing the vessel forward when the screw was turned from left to right, and drawing it back when turned in the opposite direction, whereas the sculling oar would only drive it forward.

The principle was right enough, but there was at first a great difficulty in carrying it out. Firstly, several turns of a large screw were used, and were found to need power inadequate to the effect. Then the screw was reduced to four separate blades, and now only two are used, as shown in the illustration, these saving friction, being equally powerful for propulsion, and running less risk of fouling by rigging blown overboard or other floating substances.

So much for Art. Now for the same principle as shown in Nature, of which I can take but a very few instances.

The first and most obvious example is that of the Fish-tail, which any one may observe by watching ordinary gold fish in a bowl. Their progression is entirely accomplished by the movement of the tail from side to side, exactly like that of the sculling oar, and moreover, like the oar, the tail acts as rudder as well as propeller.

The force with which this instrument can be used may be estimated by any one who is an angler, and knows the lightning-like rush of a hooked trout, or who has seen the wonderful spring with which a salmon shoots clear out of the water, and leaps up a fall several feet in height. This is not done, as many writers state, by bending the body into a bow-like form, and then suddenly straightening it, but by the projectile force which is gained by moving the tail backwards and forwards as a sculler moves his oar.

Perhaps some of my readers have seen the wonderful speed, ease, and grace with which an Otter propels itself through the water. As the otter feeds on fish, and can capture even the salmon itself, its powers of locomotion must be very great indeed. And these are obtained entirely by means of the tail, which is long, thick, and muscular, and can be swept from side to side with enormous force, considering the size of the animal. The legs have little or nothing to do with the act of swimming. The fore-legs are pressed closely against the body, and the hind-legs against each other. The latter act occasionally as assistants in steering, but that is all.

Then there are the various Seals, whose hind-legs, flattened and pressed together, act exactly like the tail of the fish, that of the otter, the oar of the sculler, or the screw of the steamer. Also, the eel, when swimming, uses exactly the same means, its lithe body forming a succession of inclined planes; so does the snake, and so does the pretty little lampern, which is so common in several of our rivers, and so totally absent from others.

I can only now give a short description of the woodcut which illustrates these points.

On the right hand Art is shown by the screw-blades of the modern steamer. In the middle is the ordinary mode of sculling a boat by an oar in the stern, and below it is the rudder, which, like the sculling oar, may be used either for propulsion or direction.

On the left hand we have three examples of the same mechanical powers as shown in Nature. The uppermost figure represents a fish as in the act of swimming, the dotted lines showing the movement of its tail, and the principle of the wedge. In the middle is an otter, just preparing to enter the water, and below is a seal, both of them showing the identity of mechanism between themselves and the art of man. I need not say that the mechanism of art is only a feeble copy of that of nature, but nothing more could be expected.

While we are on this subject I may as well mention two more applications of the screw principle. The first is the windmill, the sails of which are constructed on exactly the same principle as the blades of the nautical screw. Only, as they are pressed by the wind, and the mill cannot move, they are forced to revolve by the pressure of the wind, just as the screw of a steamer revolves when the vessel is being towed, and the screw left at liberty.

Moreover, just as the modern screws have only two blades, so, many modern windmills have only two sails, the expense and friction being lessened, and the power not injured.

Again: some years ago there was a very fashionable toy called the aërial top. It was practically nothing but a windmill in miniature, rapidly turned by a string, after the manner of a humming-top. The edges of the sails being turned downwards, the instrument naturally screwed itself into the air to a height equivalent to the velocity of the motion.

A similar idea has been mooted with regard to the guidance of balloons, or even to aërial voyaging without the assistance of gas, but at present the weight of the needful machinery has proved to be in excess of the required lifting power.

In fine, the application of the inclined plane, wedge, or screw as a motive power, is so wide a subject that I must, with much reluctance, close it with these few and obvious examples.

It is worth while, by the way, to remark how curiously similar are such parallels. I have already mentioned the very evident resemblance between the water-boatman, the water-beetles, and the human rower, the body of the insect being shaped very much like the form of the modern boat. I must now draw the attention of the reader to the similitude between the very primitive boat known by the name of Coracle, and the common Whirlwig-beetle (Gyrinus natator), which may be found in nearly every puddle. The shape of the insect is almost identical with that of the boat, and the paddle of the coracle is an almost exact imitation of the swimming legs of the whirlwig. And, as if to make the resemblance closer, many coraclers, instead of using a single paddle with two broad ends, employ two short paddles, shaped very much like battledores.

NAUTICAL.
CHAPTER III.
SUBSIDIARY APPLIANCES.—Part I.

General Sketch of the Subject.—The Mast of Wood and Iron.—Analogy between the Iron Mast and the Porcupine Quill.—The Iron Yard and its Shape prefigured by the same Quill.—Beams of the Steam-engine.—Principle of the Hollow Tube in place of the Solid Bar.—Quills and Bones of Birds.—Wheat Straws and Bamboos.—Structure of the Boat.—The Coracle, the Esquimaux Boat, and the Bark Canoe.—Framework of the Ship and Skeleton of the Fish.—Compartments of Iron Ship and Skull of Elephant.—The Rush, the Cane, and the Sugar-cane.—“Stellate” Tissue and its Varieties.

HAVING now treated of the raft, the boat, the ship, and their various modes of propulsion and guidance, we come to the subsidiary appliances to navigation, if they may be so called in lack of a better name.

First in importance is necessarily the mast; and the yards, which support the sails, are naturally the next in order. Then there come the various improvements in the building of vessels; namely, the substitution of planks fastened on a skeleton of beams for a mere hollowed log, and the subsequent invention of iron vessels with their numerous compartments, giving enormous strength and size, with very great comparative lightness.

Then we come to the various developments of the ropes or cables, by which a vessel is kept in its place when within reach of ground, whether on shore or at the water-bed. Next come the different forms of anchors which fasten a vessel to the bed of the ocean, of grapnels by which she can be made fast to the shore, or of “drags,” which at a pinch can perform either office, and can besides be utilised in searching for and hauling up objects that are lying at the bottom of the sea.

Next we come to the boat-hook, which is so useful either as a temporary anchor, or as a pole by which a boat can be propelled by pushing it against the shore or the bed of the water; and then to the “punt-pole,” which is only used for the latter purpose.

Lastly, we come to the life-belt and life-raft, which are now occupying, and rightly, so much of the public attention. These subjects will be treated in their order in the present chapter, and I hope to be able to show the reader that in all these points nature has anticipated art.

I presume that most, if not all, of my readers are aware of the rapidly extending use of iron in ship-building, not only in the standing rigging, but in the material of the vessel. First there came iron “knees,” i.e. the angular pieces of wood which strengthen the junctions of the timbers. Formerly these were made of oak-branches, and, as it was not easy to find a bough which was naturally bent at such an angle as was required for a “knee,” such branches were exceedingly valuable. Iron, however, was then employed, and with the best results. It was lighter than the wooden knee, was stronger, could be bent at any angle, and took up much less space.

By degrees iron was used more and more, until vessels were wholly made of that material. Then the masts, and even the yards, were made of iron, and, strange as it may appear, were found to be lighter as well as stronger than those made of wood. Of course, the masts and yards were hollow, and it was found by the engineers that in order to combine lightness with great strength, the best plan was to run longitudinal ridges along the inside of the tube.

A section of one of these masts is given at Fig. B, and taken from the drawings of one of our largest engineering firms. The reader will see that the mast is composed of rather slight material, and that it is strengthened by four deep though thin ribs, which run throughout its length.

When I first saw this mast I was at once struck with the remarkable resemblance between it and the quill of the Porcupine. These quills, as all anglers know, are very light, and of extraordinary strength when compared with their weight. Indeed, they are so light that they are invaluable as penholders to those who are obliged to make much use of their pen. I have used nothing else for a very long time, and the drawing of the Porcupine quill which is here given at Fig. A was made from a small piece cut from the top of the penholder which I have used for some fifteen years, and with which all my largest and most important works were written, including the large “Natural History,” “Homes without Hands,” “Man and Beast,” &c., &c. A portion of the same quill is also shown of its real size.

If the reader will cut a Porcupine quill at right angles, make a thin section of it, and place it under the microscope, or even under an ordinary pocket lens, he will see that the exterior is composed of a very thin layer of horny matter, and the interior filled with a vast number of tiny cells, which are formed much on the same plan as the pith of elder and other plants. The analogies of the pith will be treated in another page.

But were the quill merely a hollow tube filled with pith, it would be too weak to resist the strain to which it is often liable. Consequently it is strengthened by a number of internal ribs, composed of the same horny material as the outer coat, and arranged in exactly the same way as those of the mast.

There are yet other points in the structure of the Porcupine quill which might be imitated with advantage in the mast. In the first place, the internal ribs are much more numerous than those of the mast, but they are very much thinner, and taper away from the base, where the greatest strain exists, to the end, where they come to the finest imaginable edge. This modification of structure enables the outer shell of the quill to be exceedingly thin and light, and, moreover, gives to the whole quill an elasticity which is quite wonderful, considering its weight and strength.

Then, in the iron mast the exterior is quite smooth, whereas in the Porcupine quill it is regularly indented, exactly on the principle of the corrugated iron, which combines great strength with great lightness. And I cannot but think that our iron masts might be made both lighter and stronger if the shell were thinner, the internal ribs made like those of the Porcupine quill, and the shell corrugated instead of being quite smooth. The internal cells of the quill are, of course, not needed in the mast, as they are intended for nutrition, and not for strength.

Being on this subject, we may take the shape of the Porcupine quill, and compare it with that of the ship’s yard. It will be seen that the two are so exactly similar in form that the outline of one would answer perfectly well for the other. The only perceptible difference is, that in the ship’s yard both ends are alike, whereas in the Porcupine quill the end which is inserted in the skin is rounded and slightly bent, while the other end is sharply pointed.

The principal point to be noticed in the form of both quill and yard is, that they become thicker in the centre, that being the spot on which the greatest strain comes, and which, in consequence, needs to be stronger than any other part. While holding and balancing the pole which Blondin uses to preserve his balance when walking on the high rope, I was struck with the fact that the pole, which is heavily weighted at each end, had to be strengthened in the middle, exactly on the principle of the Porcupine quill and the ship’s yard. It could not, of course, be thickened, as the hands could not grasp it, but it had to be furnished with additional strengthening. And the necessity of such strengthening is evident from the fact that on one occasion the pole did break in the middle, so that any one of less nerve and presence of mind must have been killed.

Bearing in mind, then, that in a rod or pole the centre is the part which most requires to be strengthened, we can see, in cases too numerous to mention, how art has followed, though perhaps unconsciously, in the footsteps of nature. Take, for example, the beam of a steam-engine, such as is given in the sketch, and for which the great engine at Chatham acted as model. The reader will observe that in this case the beam is gradually thickened towards the centre, the ends, where the strain is slightest, being comparatively small.

Another point also must be noticed. Equal strength could have been obtained had the beam been solid, but at the expense of weight, and consequent waste of power. Lightness is therefore combined with strength by making the beam consist of a comparatively slight centre, but having four bold ridges, as shown in the section given in the accompanying illustration. This plan, as the reader will see, is exactly the same as that which is adopted in the iron mast and porcupine quill, except that the ridges are external instead of internal. The same mode of construction is employed in ordinary cranes, the principal beam of which is almost identical in form with that of the engine, both being thickest in the centre, and both strengthened with external ridges.

There are also other analogies between the hollow mast and natural objects. Keeping still to the animal world, we find the quill feathers of the flying birds to supply examples of the combination of great strength with great lightness and very little expenditure of material. Their wing bones, too, are hollow, communicating with the lungs, and are consequently light as well as strong.

Passing to the vegetable world, we find a familiar example of this structure in the common Wheat Straw. The ripe ear is so heavy, when compared with the amount of material which can be spared to carry it, that if the stalk were solid it would give way under the mere weight of the ear. Moreover, the full-grown corn has to endure much additional weight when wetted with rain, and to resist much additional force when bowed by the wind, so that a slight and solid stalk would be quite inadequate to the task of supporting the ear.

The material of the stalk is therefore utilised in a different manner, being formed into a hollow cylinder, the exterior of which is coated with a very thin shell of flint, or “silex” as it is scientifically termed. The result of this structure is that the stem possesses strength, lightness, and elasticity, so as to be equal to the burden which is laid upon it.

Then there is the common Bamboo, which is little more than a magnified straw, being constructed in much the same manner, and possessing almost the same constituents of vegetable matter and silex.

Perhaps the most extraordinary of the tubal system is to be found in the remarkable plant of Guiana called by the natives Ourah, and scientifically known by the name of Arundinaria Schomburgkii. Like the bamboo, it grows in clusters, and has a feathery top, which waves about in the breeze. But, instead of decreasing gradually in size from the base upwards, the Ourah, although it runs to some fifty feet in height, is nowhere more than half an inch in diameter. The first joint is about sixteen feet in length, and uniform in diameter throughout.

It is scarcely thicker than ordinary pasteboard, and yet so strong and elastic is it, that it can sustain with ease the weight and strain of its feathery top as it blows about in the breeze. The natives of certain parts of Guiana use this reed as a blow-gun, and I have a specimen, presented to me by the late Mr. Waterton, which is eleven feet in length.

So the reader will see that when engineers found that hollow iron beams were not only lighter, but stronger than solid beams, they were simply copying the hollow beams formed by Nature thousands of years ago.

Another great improvement in ship-building now comes before us.

We have already seen that the earliest boats were merely hollowed logs, just as Robinson Crusoe is represented to have made. But these had many disadvantages. They were always too heavy. They were liable to split, on account of flaws in the wood, and if a large vessel were needed, it was difficult to find a tree sufficiently large, or to get it down to the water when finished.

So the next idea was to build a skeleton, so to speak, of light wooden beams, and to surround it with an outer clothing, or skin, if it may be so termed. As far as I know, the two original types of this structure are the Coracle of the ancient Briton, and the birch-bark Canoe of the North American Indian, and it is not a little remarkable that both exist to the present day, with scarcely any modification.

The Coracle has been already represented on page [22]. It is, perhaps, or was in its original form, the simplest boat in existence, next to the “dug-out.” In the times of the very ancient Britons, who were content with blue paint by way of dress, and lived by hunting and fishing, the Coracle was a basin-shaped basket of wicker-work, rather longer than wide, and covered with the skin of a wild ox. This was sufficiently light to be carried by one man, and sufficiently buoyant to bear him down rapids, if he were a skilful paddler, and, of course, formed a considerable step in civilisation.

The modern Coracle is identical in form, and almost in material. The frame is still oval and basin-shaped, and made of wicker, but the outer covering is not the same. An ox-hide is an expensive article in these days, and, especially when wetted, is very heavy. So the modern Coracle builder covers the wicker skin with a piece of tarpaulin, which is much cheaper than the ox-hide, much lighter, is equally water-tight, and has the great advantage of not absorbing moisture, so that it is as light after use as before.

The Esquimaux make a boat on very similar principles. It is simply hideous in form, resembling a huge washing tub in shape, but, as it is only intended for the inferior beings called women, this does not signify.

Best, most perfect, and most graceful of all such boats is the Birch-bark Canoe of the North American Indians, whose shape has evidently been borrowed from that of a fish. I have seen many of these canoes, and have now before me several models which are exactly like the originals, except in point of size. Instead of being mere elongated bowls, like the coracle, they are long and slender, swelling out considerably in the middle, and coming to an almost knife-like edge at each end. Both stem and stern are alike, so that the canoe can be paddled in either direction, and, as one of the paddlers always acts as steersman, no rudder is needed.

The mode of construction is perfectly simple. The labour is divided between the sexes: the women cut large sheets of bark from the birch-trees, scrape and smooth them, and then sew them together, so as to form the outer skin, or “cloak” as it is called, of the canoe. Meanwhile the men are making the skeleton of strips of white cedar-wood, and binding them into shape with thongs made of the inner bark of the same tree, just like the “bass” of our gardeners. The “cloak” is then gradually worked over the skeleton, sewn into its place, and the canoe is finished. A figure of this canoe, as completed, is given in the same illustration as that which represents various forms of boat, page 7.

The last improvement is that which was caused by the necessity for large vessels, when planks or iron plates were fastened over the skeleton. But, in all these cases, the vessel is built on the principle of the thorax of a vertebrate animal, that of the whale or a fish being an admirable example. It only needs to take the skeleton of a whale, turn it on its back, and the ribs will be seen to form an almost exact reproduction of those of any ship being built in the nearest dockyard.

I have now before me the spine and ribs of a herring. The fish was over-boiled, and the flesh fell off the bones as it was being lifted out of the dish, leaving most of the ribs in their places. When held with the spine downwards, and viewed from one end, the resemblance to the framework of a ship is absolutely startling, the ribs representing the beams, and the spine taking the place of the keel. I have also before me a sketch representing a section of a Fijian canoe, and it is remarkable that even the very curve of the ribs of the herring is reproduced in those of the canoe.

Whether the Fijians derived this peculiar and beautiful curve from the ribs of a fish I cannot say, but think it very likely.

A still greater improvement in ship-building now comes before us, and this also has been anticipated both in the animal and vegetable kingdoms. There are so many examples of this anticipation that I can only give one or two.

The improvement to which I refer is that which is now almost universally employed in the construction of iron ships, namely, the making the outer shell double instead of single, and dividing it into a number of separate compartments. Putting aside the advantage that if the vessel were stove, only one compartment would fill, we have the fact that the ship is at the same time enormously strengthened and very light in proportion to her bulk.

Perhaps the best, and certainly the most obvious, example of this principle in the animal world is to be found in the skull of the Elephant. The enormous tusks, with their powerful leverage, the massive teeth, and the large and weighty proboscis, require a corresponding supply of muscles, and consequently a large surface of bone for the attachments of these muscles. Now, were the skull solid in proportion to its requisite size, its weight would be too much for the neck to endure, however short and sturdy it might be. The mode of attaining expanse of surface, together with lightness of structure, is singularly beautiful.

Perhaps some of my readers may not be aware that the bone of the skull consists of an outer and inner plate, with a variable arrangement of cells between them. In many animals, such, for example, as man, where the jaws are comparatively feeble, and the teeth small and light, the size of the skull is practically that of the brain, to which it affords a covering. The same structure may be observed in the skull of the common sparrow, where, as in man, the two bony plates are set almost in contact.

But in the elephant these external and internal plates are set widely apart, and the space between them is filled with bony cells, much resembling those of a honeycomb. They are, in fact, just the same cells as those which exist in the skull of man and sparrow, but they are very much enlarged, and in consequence give a large surface, accompanied with united strength and lightness.

There are many other examples in the animal kingdom, but our limited space will not allow them to be even mentioned.

As to the vegetable examples of this principle, they are so multitudinous that only a very slight description can be given of them.

I suppose that most boys have seen a “cane” (whether they have felt it or not is not to the purpose), and some boys have made sham cigars from pieces of cane. In either case they must have noticed that the cane is not solid, but is pierced with a vast number of holes, passing longitudinally through it, and is, in fact, a collection of little tubes connected and bound together by a common envelope.

The Sugar-cane, if cut across, is seen also to consist of multitudinous cells, which, however, are not hollow, but filled with the sweet liquid from which sugar is obtained by boiling. Then there are many of our common English plants, like the ordinary rush or reed, which are very slight in diameter in comparison with their length, and in which the cells are still further strengthened and lightened by the projection of their sides into a number of points which meet each other, and leave interstices between them. This modification of the cellular system is called “Stellate” (or star-like) Tissue, and two examples of it are given in the illustration, one being taken from the common rush, and the other from the seed-coat of the privet. A very good specimen of stellate tissue may be obtained by cutting a thin section of the white inner peel of the orange.

NAUTICAL.
CHAPTER IV.
SUBSIDIARY APPLIANCES.—Part II.

The Cable and its Variations.—Material of Cables.—Hempen and Iron Cables, and Elasticity of the latter.—Natural Cables.—The “Byssus” of the Pinna and the common Mussel.—The Water-snail and its Cable.—A similar Cable produced by the common White Slug.—The Principle of Elasticity.—Elastic Cable of the Garden Spider.—Tendrilous Cables of the Pea and the Bryony.—The Vallisneria, and its Development through the Elastic Cable.—Proposed Submarine Telegraph Cable.—The Anchor, Grapnel, and their Varieties.—Natural Anchors.—Spicule of Synapta.—The Grapnel, natural and artificial.—Ice-anchor and Walrus Tusks.—The Mushroom Kedge.—The Flesh-hook.—Eagle-claw.—The Grapple-plant of South Africa.—The Drag.

AMONG the most important accessories to a ship are the Cable, by which she can be anchored to the bed of the sea, and the ropes called “warps,” by which she can be fastened to the land.

Perhaps my readers may not know the old riddle—“How many ropes are there on board a man-of-war?” The non-nautical individual cannot answer, but the initiated replies that there are only three, namely, the man-rope, the tiller-rope, and the rope’s-end, all the others being “tacks,” “sheets,” “haulyards,” “stays,” “braces,” &c.

Formerly cables were always made of hemp, enormously thick, and most carefully twisted by hand. Now, even in small vessels, the hempen cable has been superseded by the iron chain, and this for several reasons.

In the first place, it is much smaller in bulk, and therefore does not occupy so much room. In the next place, it is even lighter than the hempen cable of corresponding strength; and, in the third, its specific gravity—i.e. its weight when compared with an equal bulk of water—is so great, that when submerged, it falls into a sort of arch-like form, and so attains an elasticity which takes off much of the strain on the anchor, and protects it from dragging.

We will now look to Nature for Cables.

The natural cable which will first suggest itself is evidently that of the Pinna Shell (Pinna pectinata), which fixes its shell to some rock or stone with a number of silk-like threads, spun by itself, and protruding from the base, just as a vessel on a lee shore throws out a number of cables. The threads which compose the “byssus,” as it is called, are only a few inches in length, and apparently slight. They are, however, really strong, and by acting in unison enable the shell, though sometimes two feet in length, to be held firmly to the rock. I may here mention that they have been occasionally woven into gloves, and other articles of apparel, to which their natural soft grey-brown hue gives a very pleasing appearance.

A still more familiar instance of a natural marine cable is given by the common Mussel, which can be found in thousands on almost every solid substance which affords it a hold. Even copper-bottomed ships are often covered with Mussels, all clinging by their natural cables, and it is thought that the cases which sometimes occur of being poisoned by eating Mussels, or “musselled,” as the malady is called by the seafaring population, are due to the fact that the Mussels have anchored themselves to copper, and have in consequence imbibed the verdigris.

Passing from salt to fresh water, we come to a natural cable which is very common, and yet, on account of its practical invisibility, is almost unknown, except by naturalists. I refer to the curious cable which is constructed by the common Water-snail (Limnæa stagnalis), which has already been mentioned in its capacity of a boat.

This creature has a way of attaching itself to some fixed object, such as a water-lily leaf, by means of a gelatinous thread, which it can elongate at pleasure, and by means of which it can retain its position in a stream, or in still water can sink itself to the bottom, and ascend to the same spot. This cable seems to be made of the same glairy secretion as that which surrounds the egg-masses which are found so plentifully on leaves and stones in our fresh waters, and, like that substance, is all but invisible in the water, so that an inexperienced eye would not be able to see it, even if it were pointed out.

Slight, gelatinous, and almost invisible in the water as is this thread, its strength is very much greater than might be supposed. Not only can a mollusc be safely moored in the water by such a cable, but it can be actually suspended in the air, as may be seen from a letter in Hardwicke’s Science Gossip for 1875, p. 190:—

“Last summer (September 29) I met with the following unusual fact. In a green-house, from a vine-leaf which was within a few inches of the glass ... a slug was hanging by a thread, which was more than four feet in length, not unlike a spider-web, but evidently much stronger.

“The slug was descending by means of this thread, and, as the glutinous matter from the under part of the body was drawn out by the weight of the creature, it was consolidated into a compact thread by the slug twisting itself in the direction of the hands of a clock, the power of twisting being given by the head, and the part of the body nearest the head being turned in the direction of the twist. There was no tendency to turn in the contrary direction. Evidently the thread became hard as soon as it was drawn away from the body.

“By wetting the sides of slips of glass, I secured two specimens of the thread. In one of these, part was stretched, and part quite loose, the latter appearing flat when seen through a microscope. The thread, which was highly elastic, was increased about three inches in a minute. The slug was white, and about an inch and a half in length.”

Now we come to the elastic system of the Chain Cable, and find it anticipated in Nature in various ways.

One curious example was that of a Spider, which found its wheel-like net in danger from a tempestuous wind. The Spider descended to the ground, a depth of about seven feet, and, instead of attaching its thread to a stone or plant, fastened it to a piece of loose stick, hauled it up a few feet clear of the ground, and then went back to its web. The piece of stick thus left suspended acted in a most admirable manner, giving strength and support, and at the same time yielding partly to the wind.

By accident the thread became broken, and the stick, which was about as thick as an ordinary pencil, and not quite three inches in length, fell to the ground. The Spider immediately descended, attached another thread, and hauled it up as before. In a day or two, when the tempestuous weather had ceased, the Spider voluntarily cut the thread, and allowed the then useless stick to drop.

A curious example of the elastic cable is seen in the egg-case of the Dog-fish, which is given on page [35]. The egg-case is formed like that of the common skate, and has a projection from each of its angles. But the projections, instead of being mere flattened horns, are lengthened into long elastic strings, tapering towards the ends, and twisted spirally, like the tendrils of a grape-vine.

These tendril-like appendages twist themselves round seaweeds and other objects, and, on account of their spiral form, can hardly ever be torn from their attachments. Sometimes after a storm the egg is thrown on the shore, still clinging to the seaweed, but to find an egg detached is very rarely done.

I have already mentioned the tendrils of the vine, and their great strength. The reader may remember the corresponding cases of the Pea and the Bryony, the latter being a most remarkable example of the strength gained by the spiral form. It clambers about hedges, is exposed to the fiercest winds, has large and broad leaves, and yet such a thing as a Bryony being blown off a hedge is scarcely, if ever, seen. I never saw an example myself, though I have had long experience in hedges.

Another excellent example of this principle is found in the Vallisneria plant, which of late years has become tolerably familiar to us through the means of fresh-water aquaria, though it is not indigenous to this country.

In this plant the elastic power of the spiral cable is beautifully developed. It is an aquatic plant, mostly found in running waters, and has a most singular mode of development. It is diœcious—i.e. the male, or stamen-bearing, and the female, or pistil-bearing flowers, grow upon separate plants.

It has to deposit its seeds in the bed of the stream, and yet it is necessary that both sets of flowers should be exposed to the air and sun before they become able to perform their several duties. Add to this the fact that the male flower is quite as small in proportion to the female as is the case with the lac and scale insects, and the problem of their reaching each other becomes apparently intricate, though it is solved in a beautifully simple manner.

Fertilisation cannot be conducted by means of insects, as is the case with so many diœcious terrestrial plants, and it is absolutely necessary that actual contact should take place between them. This difficult process is effected as follows:—

The female flowers are attached to a very long spiral and closely coiled footstalk, and, when they are sufficiently developed, the footstalk elongates itself until the flower rests on the surface of the water, where it is safely anchored by its spiral cable, the coils yielding to the wavelets, and keeping the flower in its place.

Meanwhile the tiny male flowers are being developed at the bottom of the river, and are attached to very short footstalks. When they are quite ripe they disengage themselves from their footstalks, and rise to the surface of the river. Being carried along by the stream, they are sure to come in contact with the anchored female flowers. This having been done, and the seeds beginning to be developed, the spiral footstalk again coils itself tightly, and brings the seeds close to the bed of the stream, where they can take root.

There are other numerous examples, of which any reader, even slightly skilled in botany, need not be reminded, most of them being, in one form or another, modifications of the leaf or the petal, which, after all, are much the same thing. The vine and passion-flower are, however, partial exceptions.

I may here mention that soon after the failure of the first Atlantic telegraph cable, an invention was patented of a very much lighter cable, enclosed in a tube of india-rubber, and being coiled spirally at certain distances, so that the coils might give the elasticity which constitutes strength. The cable was never made, its manufacture proving to be too costly; but the idea of lightness and elasticity, having been evidently taken from the spiral tendrils of the bryony, was certainly a good one, and I should have wished to see it tried on a smaller scale than the Atlantic requires.

As a natural consequence, after the cable comes the Anchor, which in almost every form has been anticipated by Nature, whether it be called by the name of anchor, kedge, drag, or grapnel.

On the accompanying illustrations are shown a number of corresponding forms of the Anchor, together with a few others, which, although they may not necessarily be used in the water, are nevertheless constructed on the same principle—i.e. for the purpose of grappling.

One of the most startling parallels may be seen on the right hand of the illustration, the figure having been drawn from an old Roman coin. On the other side of the same illustration may be seen an anchor so exactly similar in form, that the outline of the one would almost answer for that of the other. This object is a much-magnified representation of a spicule which is found on the skin of the Synapta, one of the so-called Sea-slugs, which are so extensively sold under the name of Bêche de Mer. It forms one of the curious group called the Holothuridæ.

Each of these anchors is affixed to a sort of open-worked shield, as shown above, and on the left hand; and it is a curious fact that in the various species of Synapta the anchor is rather different in form, and the shield very different in pattern. They are lovely objects, and I recommend any of my readers who possess a microscope to procure one. They need a power of at least 150 diameters to show their full beauties.

An ordinary Grapnel is here shown, and in the corresponding position on the opposite side is an almost exactly similar object, except that it is double, having the grapnel at both ends of the stem. This is a spicule of a species of sponge, and is one of the vast numbers of which the sponge principally consists.

Next to the sponge-spicule is a still more perfect example of a natural Grapnel. This is the head of an internal parasite called Echinococcus, which holds itself in its position by means of the circle of hooks with which the head is surrounded. These hooks are easily detached, and have a curious resemblance to the claw of the lion or tiger.

On the left-hand side is a representation of a parasitic crustacean animal called Lernentoma, which adheres to various fishes, and is mostly found upon the sprat, clinging to the gills by means of its grapnel-shaped head.

On the right hand of the accompanying illustration is an ice-anchor, copied from one of those which were taken out in the Arctic expedition of 1875. Opposite is the skull of the Walrus, the tusks of which are said to be used for exactly the same purpose. Below are ice-hooks, also used for the same expedition.

The next illustration exhibits a butcher’s hook and a common porter’s hook, by which he lifts sacks on his back; and opposite them are some sponge-spicules, the similarity of which in form is so remarkable that the former might have been copied from the latter.

Our next sketch shows a remarkable example of similitude in form. There are certain small anchors called Kedges, which are very useful for mooring a boat where no great power of resistance has to be overcome, and a large anchor would be cumbersome. One of these is called, from its shape, the “Mushroom Kedge,” and is very useful, as, however it may be dropped, some part of the edge is sure to take the ground. This Kedge is shown on the right hand of the illustration, and the Mushroom, from which its shape was borrowed, is seen on the left.

We now come to some more examples of the principle of the Grapnel, some of which are applied to nautical, and others to terrestrial objects.

The right-hand upper figure represents the “Flesh-hook,” used for taking boiled meat out of the caldron, so familiar to us by the reference to it in Exodus xxvii. 3, and the still better-known allusion to its office in 1 Samuel ii. 13, 14. In the former passage, even the material, brass, which was really what we now call bronze, is mentioned, and it is a curious fact that all the specimens in the British Museum, from one of which the drawing was taken, are made of bronze. I need hardly state that the hollow handle is meant to receive a wooden staff.

On comparing this figure with that of the Eagle’s foot on the opposite side, the reader cannot but be struck with the exact resemblance between the two. Indeed, there is very little doubt that the flesh-hook was intentionally copied from the foot of some bird of prey. Perhaps the Osprey would have furnished even a better example than the Eagle, the claws being sharper and more boldly curved, so as to hold their slippery prey the better.

On the left hand of the next illustration is a figure of the seed-vessel of the Grapple-plant of Southern Africa, drawn from a specimen in my collection. The seed-vessel is several inches in length, and the traveller who is caught by a single hook had better wait for assistance than try to release himself. The stems of the plant are so slender, and the armed seed-vessels so numerous, that in attempting to rescue one portion of the dress, another portion becomes entangled, and the traveller gets hopelessly captured. Besides the hooks of the seed-vessels, the branches themselves are armed with long thorns, set in pairs. The scientific name of this plant is Uncinaria procumbens, the former word signifying “a hook,” and the latter “trailing.” It is also known by the popular name of Hook-plant.

In the late Kafir wars the natives made great use of this and other plants with similar properties, their own naked, dark, and oiled bodies slipping through them easily and unseen, while the scarlet coats of the soldiers were quickly entangled, and made them an easy mark for the Kafir’s spear. In this way many more of our soldiers were killed by the spears than by the bullets of their enemies.

Opposite to the Grapple-plant is shown the common Drag, which is utilised for so many purposes. Generally it is employed for recovering objects that have sunk to the bottom of the water, and its use by the officers of the Humane Society is perfectly well known, the Drag being sometimes affixed to the end of a long pole, like the flesh-hook already described, and sometimes tied to a rope.

It can also be used as an anchor, after the manner of a kedge, and has been often employed in naval engagements for the purpose of drawing two ships together, and preventing the escape of the vessel which is being worsted. My relative, the late Admiral Sir J. Harvey, K.B., used drags in this manner, and secured two French ships, one on either side, namely, L’Achille and Le Vengeur. The first was sunk, and the second captured.

NAUTICAL.
CHAPTER V.
SUBSIDIARY APPLIANCES.
Part III.—The Boat-hook and Punt-pole.—The Life-buoy and Pontoon-raft.

The Boat-hook and its varied Uses.—The Earth-worm and the Serpula.—Microscopic Boat-hooks.—The Life-belt.—Life-boats and their Structure.—Uses of Cork.—Wine Corks made serviceable.—The Life-collar.—Portuguese Man-of-war.—Captain Boyton’s Life-dress.—The Life-raft.—Victualling a Yacht and Boat.—The Janthina and its Air-vessels.—Cask-pontoon—Pottery-raft and its Uses.

AS all rowing men know, an indispensable appliance to the boat is the Boat-hook, which can be used either as a pole, wherewith to push the boat along, or as a grapnel, by which it can be drawn towards the shore or a ship. As the latter portion has been discussed at the close of the preceding chapter, we may proceed to the former.

Every one knows how a boat may be propelled by a pole pressed against the bank or the bottom of the water, and that there are certain boats, called punts, which are propelled in no other way.

Now, the punt-poles and boat-hooks, of which some examples are given in the accompanying illustration, have long been anticipated in Nature, there being many creatures which have no other mode of progression; such, for example, as the common Earth-worm, which pushes itself along by certain bristles which project from the rings of which the body is composed, and which have the power of extension and contraction to a wonderful extent. As, however, I shall advert to these in another part of the work, I will content myself at present with a single example, namely, the beautiful marine worm known as the Serpula.

This worm lives in a shelly tube, which is lined with a delicate membrane, up and down which it passes with ease, ascending slowly, but generally descending with such wonderful rapidity that the eye cannot follow its movements. The latter movement will be explained in a subsequent part of the book, and we will at present only treat of the former.

If the creature be removed from the tube, and carefully examined, a number of projections will be seen, in each of which is a perforation. If the animal be pressed, a slight glass-like bristle passes through the perforation, and can easily be removed. If properly treated, and placed under a high power of the microscope, the tiny bristle resolves itself into the remarkable object which is shown on the left hand of the illustration.

It consists of a number of spear-like rods, each having a straight shaft, and a curved and pointed tip, deeply barbed on the inner portion of the curve. These curious bundles of spicules can be protruded or retracted at pleasure, and, as they are all directed backwards, it is evident that when they are pushed against the sides of the tube, either the points or the barbs must catch against the membrane which lines the tube, and so propel the animal upwards. When it wishes to descend, it uses another set of implements, and withdraws the first within their sheaths.

This is exactly analogous to the mode of progression employed by punters, who, after they have placed the pole against the bed of the stream, and run along the punt so as to push it as fast as possible, immediately withdraw the pole, and take it to the head of the punt, ready for another push. This, as the reader will see, is exactly the plan pursued by the Serpula in lengthening itself when it wishes to advance, and so to press its spicules against the sides of its tube, and in shortening itself and withdrawing the spicules ready for another push.

Another needful accessory of vessels now comes before us, namely, the capability of forming rafts or life-belts, which will float under any circumstances. Here, again, every human invention of which I know has been anticipated by Nature. Take, for example, the familiar instance of the cork life-belt and the cork edgings of the life-boat. Both are constructed on the same principle, i.e. the maintenance of cells which are filled by air instead of water, and are impervious to the latter.

The material most used for this purpose is cork, and life-belts constructed of it have long been in well-deserved use, the cork-bark having the property of holding much air and excluding water. Many of our life-boats are furnished with a broad and thick streak of cork, so that even if the boat be filled with water and upset, she will right herself and swim. I regret to say that many of the so-called “life-belts” which are offered for sale ought rather to be called “death-belts,” they having been found to be filled with hay and straw, with only a few shavings of cork just under the covering of the belt.

Indeed, so buoyant is this substance that a very efficient belt can be made by stringing together three or four rows of ordinary wine corks, and tying them round the neck like a collar. Under these circumstances it is simply impossible to sink, and though any one may collapse from exhaustion, drowning is almost out of the question. The now well-known cork mattress, which is used in many ships, is another example of the same principle.

Lately there has been invented a “life-collar,” which possesses similar advantages, but occupies less space when not wanted. It is nothing more than a tube of caoutchouc, which can be inflated at pleasure, and tied round the neck. The ordinary life-belt goes round the waist, and needs much more material without obtaining a better result, which is simply the keeping of the mouth and nostrils out of the water.

Perhaps the most buoyant of living beings is the Portuguese Man-of-war (Physalis pelagicus), which floats on the surface of the ocean like a bubble. It can at pleasure distend itself with air and float, or discharge the air and sink.

Now, there is a very remarkable swimming dress, which, though not entirely invented, was at least perfected by Captain Boyton, and which, as it enabled the wearer to cross from France to England under rather unfavourable circumstances, is clearly a most valuable invention.

Whether the inventor knew it or not I cannot say, but the Boyton life-dress is simply a modification of the Physalis, being capable of dilatation with air at will.

So much for the individual life-belt, and we will now pass to those which are intended to sustain more than one individual. It has almost invariably been found that when a ship has been wrecked on a rock, or stove in by the sea, that, although there may be plenty of boats, there is great difficulty in getting them into the water rightly.

Now, if parts of the ship itself could be made of materials which could not be sunk except by enormous pressure, and which might be released by a touch if the vessel were sinking, it is evident that many lives would be saved which have now been lost.

And if such movable parts of the vessel were supplied with water and provisions in air-tight cases, there is no doubt that the number of “missing” ships would be very greatly diminished. I remember an instance where a yacht was “hung up” on a mud-bank, whence there was no escape, for twenty-four hours, and there was one sandwich on board to be divided among the owner, two men, and a boy. Of course the boy had the sandwich, and the men sustained themselves as well as they could with tea, of which there was, fortunately, a canister on board. As it was, they were some thirty-six hours without food.

After such an experience the owner had special lockers made in the yacht and her boat, containing biscuit, potted meats, water, wine, spirits, tobacco, tea, an “etna” for heating the water, and matches. Of course these were on a smaller scale in the boat; but several thick rugs were also stowed away, in case of being separated from the yacht at night. It so happened that they were never needed; but the sense of security which they imparted was worth ten times the expense and trouble, which included a careful inspection of all the stores before each voyage.

In Nature there is just such a raft as is needed, capable of carrying a heavy freight, and which cannot be upset. And it is rather remarkable that it has been unconsciously imitated in various parts of the world.

This is the singular apparatus attached to the Violet Snail (Janthina communis), which is common enough in the Atlantic, and derives its name of Violet-shell from its beautiful colour. The chief interest, however, centres in the apparatus which is popularly called the “raft,” and which sustains the shell and eggs. It is made of a great number of air-vessels, affixed closely to each other, and by the curious property of bearing its cargo slung beneath it instead of being laid upon it.

Beneath the raft are the eggs, or rather, the capsules which contain the eggs, and at one end is the beautiful violet shell itself. The floating power of the raft is really astonishing, and even in severe tempests, when it is broken away from the animal, the raft continues to float on the surface of the waves, bearing its cargo with it.

On the opposite side of the illustration are two examples of rafts constructed so exactly on the same principle as that of the Violet Snail, that they both might have been borrowed from it.

The upper is the kind of raft which has often been constructed by sailors when trying to escape from a sinking ship, or by soldiers when wishing to convey troops across a river, and having no regular “pontoons” at hand. It is made simply by lashing a number of empty casks to a flooring of beams and planks.

The amount of weight which such a structure will support is really astonishing, as long as the casks remain whole, and to upset it is almost impossible. Even cannon can be taken across wide expanses of water in perfect safety, and there is hardly anything more awkward of conveyance than a cannon, with its own enormous and concentrated weight, and all the needful paraphernalia of limber, ammunition (which may not be wetted, and of immense weight), horses, and men.

Yet even this heterogeneous mass of living and lifeless weight can be carried on the cask-raft, which is an exact imitation of the living raft of the Violet Snail.

Beneath the cask-pontoon is to be seen a sketch of a very curious vessel which is in use on the Nile, and I rather think on the Ganges also, though I am not quite sure. It is formed in the following manner:—

In both countries there are whole families who from generation to generation have lived in little villages up the river, and gained their living by making pottery, mostly of a simple though artistic form, the vessel having a rather long and slender neck, and a more or less globular body.

When a man has made a sufficient number of these vessels, he lashes them together with their mouths uppermost, and then fixes upon them a simple platform of reeds. The papyrus was once largely used for this purpose, but it seems to be gradually abandoned.

He thus forms a pontoon exactly similar in principle with the cask-pontoon which has just been described. Then, taking his place on his buoyant raft, he floats down the river until he comes to some populous town, takes his raft to pieces, sells the pots and reeds, and makes his way home again by land.

WAR AND HUNTING.
CHAPTER I.
THE PITFALL, THE CLUB, THE SWORD, THE SPEAR AND DAGGER.

Analogy between War and Hunting.—The Pitfall as used for both Purposes.—African Pitfalls for large Game, and their Armature for preventing the Escape of Prey.—Its Use in this Country on a miniature scale.—Mr. Waterton’s Mouse-trap.—Pitfall of the Ant-lion, and its Armature for preventing the Escape of Prey.—The Club and its Origin.—Gradual Development of the Weapon.—The “Pine-apple” Club of Fiji.—The Game of Pallone and the “Bracciale.”—The Irish Shillelagh.—Clubs and Maces of Wood, Metal, or mixed.—The Morgenstern.—Ominous Jesting.—Natural Clubs.—The Durian, the Diodon, and the Horse-chestnut.—The Sword, or flattened and sharpened Club.—Natural and artificial Armature of the Edge.—The Sword-grass, Leech, and Saw-fish.—Spears and Swords armed with Bones and Stones.—The Spear and Dagger, and their Analogies.—Structure of the Spear.—The Bamboo as a Weapon of War or Hunting.—Singular Combat, and its Results.

THE two subjects which are here mentioned are practically one, the warfare being in the one case carried on against mankind, and in the other against the lower animals, the means employed being often the same in both cases.