Nature's Teachings

CHAPTER V.
THE PRINCIPLE OF THE SPRING.—THE ELASTIC SPRING.—ACCUMULATORS.—THE SPIRAL SPRING

Springs and their various Structure.—The Elastic Spring.—The Boy’s Catapult and its Powers.—The Pistolograph, its Principle, and Uses to which it can be put.—Leaf-rolling Caterpillars, and their Way of Work.—The Carriage Spring.—The Horse’s Hoof and its complex Structure.—Fungi and their united Power.—The Chinese Cross-bow.—The ancient Balista.—Skull of the Crocodile.—Bones of young Children.—The Spiral Spring and its many Uses.—The Toy-gun.—The Needle-gun.—Valved Brass Instruments.—Watch and Clock Springs.—The Bed Spring.—Parallels in Nature and Art.—Buffers of Railway Carriages.—Spring Solitaires.—The Bell Spring.—Spiral Springs in Vegetable Tissues.—Poison Cells of various Marine Animals.—Effects of the Spiral Springs.

Elastic Springs

HERE we come upon a subject so large, that it is difficult to define its exact requisite limits. The principle of the elastic spring pervades all Nature, and the numerous adaptations in Art are closely, though perhaps not directly, attributable to the wide distribution of the spring in Nature.

There is, for example, the simple elasticity which enables a tree, when bowed by the wind, to spring back so soon as the pressure is removed, and which, indeed, is the power which enables a bow to propel an arrow. Then there are spiral springs innumerable, many of them so minute that they can only be seen by the aid of the microscope, and there are many springs which exhibit their elasticity by their power of extension and shortening, just as is done with the elastic fabrics which are so much in vogue at the present day, and which seem so necessary to ordinary comfort that we feel disposed to wonder how our forefathers managed without them.

We will now proceed to examine some of these springs in detail.

There is one form of elastic spring which has of late years become more familiar than agreeable, namely, the toy which is learnedly called a “catapult,” though it has little in common with the ancient weapon whose name it bears.

As may be seen by reference to the illustration, it consists of one or more india-rubber straps attached to a fork-like handle, and carrying a small pouch in which is contained the missile. Although it is not remarkable for accuracy, it can throw a stone or a bullet a considerable distance, and its power can be very quickly increased by adding to the number of the straps. Thus a catapult has been made which was capable of sending a small pistol bullet through a wooden board, so that the child’s toy might really become a dangerous weapon.

Indeed, cases are known where the catapult has hurled a stone with fatal effect upon human beings. In my own neighbourhood there are many examples of glass being pierced by stones thrown from catapults just as if they had been subjected to bullets shot from firearms, the holes being quite small and round.

The power of accumulating force by increasing the number of springs was utilised by Mr. Scaife, when he invented his wonderful photographic machine which he termed the “Pistolograph,” on account of the sound which was produced when the portrait was taken.

The idea was simple enough, though the practice of it was not so easy. He wished to be able to take a photograph with an exposure of the least possible time, and thus to attain freedom and action, instead of the dull stiffness which generally characterizes photograph portraits. The mode which he adopted was by introducing a peculiarly sensitive film, which would take an impression in a mere moment, and then arranging the machine so that an exposure of more than a moment was impossible.

This was done by covering the lens with an exactly fitting door, revolving on a pivot. The axis on which the door revolved was attached to a number of india-rubber bands, exactly like those which are used for confining papers. As the power of the springs increased with their number, it naturally followed that the rapidity of the revolution was in exact ratio with the number of the bands, so that the duration of exposure to light could be measured with tolerable accuracy.

So wonderfully well did this plan succeed that photographs of eclipses were taken with perfect accuracy, a matter of great importance when time has to be considered. Horses were also taken at full gallop, so as to display their action, and the crowning achievement was the photographing of a cannon in the act of firing, and the bursting of a charged shell. So rapid is the action of the instrument, that in several cases where a cannon or mortar had been photographed, even the track of the ball or shell is visible.

It necessarily followed that when the springs caused the circular cover to revolve with such rapidity, they made it close with a sharp report, and so gave rise to the name of the machine. Moreover, as it had to be used for rapidly moving objects, it was not fixed on a pedestal, but was held in the hands, while aim was taken at the object, just as with a pistol. When the observer thought that he had his aim correct, he touched a trigger, round spun the cover, and the photograph was taken.

On the right hand of the illustration is seen the Catapult, made with several springs, and on the left is shown an example of the Accumulator as formed by Nature.

The reader may probably be acquainted with the Leaf-rolling Caterpillars, of which there are so many. I had often inspected these curled leaves, and, on comparing them with the size of the caterpillars, had noticed that the muscular strength of the insect was quite inadequate to the work which was done. That much of it was owing to the “bowsing” system, which has already been described when treating of the Toggle-joint, was very probable, but that some other force must be employed was evident.

On unrolling a leaf, the hidden force was at once explained, and showed itself to be a system of accumulators exactly like those of the pistolograph or the catapult. The caterpillar spins successive belts of silken threads, and affixes them to the leaf, as shown in the illustration. These threads are nearly as elastic as the india-rubber bands of the catapult, and accordingly draw the leaf together. Another set of belts is added above the former, and, as they harden and contract in the air, they roll the leaf still further. The first row is then shortened and tightened, and a third and fourth row are added in the same fashion. So elastic are these belts, that if the leaf be carefully handled it can be almost wholly unrolled, and will spring back again as soon as the force is removed.

Another form of accumulated force may be seen in the ordinary Carriage Spring, one of which is shown in the illustration. It is made of a number of strips of elastic steel lying upon each other, and suffered to play upon each other by means of slots and rivets. The weight being placed in the centre, it is evident that this very ingenious spring is really an elastic girder, yielding to sudden pressure, and recovering itself when that pressure is removed.

Ingenious as is this spring, it has many parallels in Nature, one of which is here given.

It is popularly thought the hoof of the horse is a solid mass of horn destined to protect the feet against hard and rough ground. Such certainly seems to be the opinion of farriers, who, in shoeing horses, act exactly as if the horn of the hoof were structureless; whereas it is a marvel of complicated mechanism. On looking at the exterior of a horse’s hoof, it will be seen to be marked with a vast number of very fine, but easily visible longitudinal lines, looking as if they were scratches from a very fine needle. If the hoof be removed from the foot, and examined upon the interior, it will be seen that each of the apparent scratches signifies the edge of a very thin plate of horn, not so thick as the paper on which this book is printed. The hoof, in fact, is built up of multitudinous plates of horn, set side by side, and each acting as a separate spring. It is this beautiful structure which allows the horse to tread without a jar being sent through its whole system by every step which it takes.

A similar structure is to be found in all hoofed quadrupeds, and is especially noticeable in the case of the Elephant. All those who have watched the walk of an Elephant, no matter what its size may be, must have been struck with the curious noiselessness of its movements. Its weight may be measured by tons, and yet the enormous animal steps as noiselessly as a cat. On examining one of the hoofs, after it is removed from the foot, the cause of this marvellously silent tread is perfectly evident. The whole of the hoof is composed of nearly parallel horny plates, and by their united action they produce the required result.

Each plate in itself is very feeble, but, when united as they are at the ends, they afford mutual support to each other. Similarly the separate feathers in a couch would be crushed by a comparatively slight weight, but when a number are confined together they support each other, and form the soft, yielding couch with which we are so familiar. Horsehair, when used as the stuffing for a couch or chair, acts in the same way, and so do the fine filaments of wool when used under the name of “flock.”

Another good example of the power of accumulated force, although it has no direct relation to the spring, is the well-known fact that fungi, which are separately so fragile, are capable of lifting and retaining in the air stones so large that two men could hardly carry them. Were the stones laid down upon the fungi, the latter would be crushed, but, as they grow beneath the stones, they accumulate their powers, and slowly, but certainly, raise the weight from the ground.

This very principle of accumulated force has long been used in weapons of war, and I possess several examples of such weapons. One of them is a Chinese repeating Cross-bow, which was taken at the capture of the Peiho Fort, and was really a formidable wall-instrument, carrying a reserve of arrows, and delivering them with great rapidity. In point of fact, it consists of three bows, placed upon each other, and playing upon each other just as do the portions of a carriage spring. Such strength is thus obtained, that the bow cannot be drawn by hand, but is worked with a lever, as shown in the illustration. The whole machinery of the weapon, including the self-notching and self-supplying system, is very interesting, but is outside our present object. The very powerful bow of the ancient Balista was made on the same principle, and was strong enough to throw large stones and wooden beams.

I also have bows in my collection which are strengthened on the same principle, though not exactly in the same manner. There are several Indian, Chinese, and Japanese bows which are curved almost like the letter C, and have to be reversed when strung. These bows are of no very great size, but possess wonderful elasticity. They owe the latter quality to sundry layers of sinew which have been affixed to the back when wet, and which add enormously to the power of the bow, while they very little enlarge its dimensions.

Another bow, made by the natives of Vancouver’s Island, has the back strengthened by a number of cords spun from sinew fibres, and possessing the strength and elasticity to which we are accustomed in the strings of the harp, guitar, or violin.

We will now turn to a parallel in Nature. This is to be found in the lower jaw of the Crocodile, as is pointed out by Professor Owen, in his work on the “Skeleton and the Teeth.”

All persons who have a smattering of anatomy are aware that even in the human body the most solid bones of the adult were originally composed of several pieces, and that they only become fused together in course of time. The jaw-bones, for example, were once so composed, and in the Crocodile the junction is never completed, the pieces of bone remaining separate, but being pressed firmly against each other during life.

I have now before me the skull of a Gangetic Crocodile, in which, although the animal was an adult when killed, the bones of the long lower jaw are so loose that unless they were tied together the jaw would fall to pieces.

This analogy between Art and Nature is thus described by Professor Owen in the work which has just been mentioned:—

“The purpose of this subdivision of the lower jaw-bone has been well explained by Conybeare and Buckland, by the analogy of its structure to that adopted in binding together several parallel plates of elastic wood or steel to make a crossbow, and also in setting together thin plates of steel in the carriage spring.”

Dr. Buckland also adds: “Those who have witnessed the shock given to the head of a Crocodile by the act of snapping together its thin, long jaws, must have seen how liable to fracture the lower jaw would be were it composed of one bone only.... The splicing and bracing together of thin flat bones of unequal length and of varying thickness afford compensation for the weakness and risk of fracture that would otherwise have attended the elongation of the parts.”

A good example of the value of this structure of bone may be found in young children. Before they are old enough to take care of themselves they are perpetually falling down, and never hurting themselves. I have seen a little girl of five years old roll from top to bottom of a lofty staircase. It looked as if the child must be killed, but she was only giddy with her many revolutions, and a little bruised about the elbows. The reason of this curious immunity from injury is, that the bones, especially those of the skull, are not completely united, and so act on the principle of the compound spring.

The Spiral Spring

This subject is so large, and there are so many examples, both in Art and Nature, that it is not very easy to make selections which will sufficiently answer the purpose.

The upper left-hand figure of the illustration represents the ordinary Spiral Spring made of wire, and used for its power of resuming its shape when compressed. In early childhood most boys have had practical experience of this spring in the toy guns and cannons with which they are supplied. The spring is compressed by the ramrod, and held in its place by a catch. If a pellet be placed in the gun, and the catch released by pulling the trigger, the spring flies back to its former shape, and drives the pellet.

An exactly similar spring is used in the well-known “Needle-gun,” the spring driving a needle through the explosive mixture, and so igniting the charge.

Our brass instruments would be very badly off without the spiral spring, which is placed under the pistons. The elasticity allows the pistons to be pressed down, and when the fingers are raised the pistons spring up again.

Another form of this instrument is seen on the right of the ordinary spring. This is used in the manufacture of spring mattresses and couches, and is made thinner in the centre, so as to allow of greater elasticity.

Below them is the spring which is used for watches and clocks, one end being fastened to the rim of the barrel, and the other to the pivot. When the latter is turned the spring becomes “wound up,” and, when released, keeps the works going by pressing against them. Of the “pall-and-ratchet” wheel, by which the movements are retarded, we shall treat in another place.

On the left hand of the illustration are a few figures of the Spiral Spring as seen in Nature.

On the extreme left of the group is a spiral cell taken from the flower-stem of the Water-lily. As the reader will see, it is composed of a number of fibres laid parallel to each other, and twisted into a hollow spiral. In order to exhibit its shape the better, the spiral has been partially uncoiled.

On the extreme right is a corresponding spiral cell from the common Lily, in which the spring power is given by two fibres twisted in opposite directions. The reader will now understand and admire the mechanism by which these plants attain their great strength and elasticity, the stems being made of myriads of these spiral fibres.

The oval body on the upper part of the illustration is a poison-cell of a marine polyp, and is given here as an example of an animal spiral spring, the others all belonging to the vegetable world.

We shall see more of its structure a little further on, and will not now examine it in detail.

The two remaining figures represent the remarkable objects called Antherozoids, i.e. the living creatures of anthers. They exist in vast numbers in the non-flowering plants, and inhabit those parts which correspond with the anthers of the flowering plants. When placed in water they have a curious way of coiling and twisting themselves spirally, so as to make their way through the water in a tortuous, but tolerably rapid, course. This movement is effected by the contraction and expansion of the spirally twisted filament. The upper figure represents a group of Antherozoids in their cells, and the lower is a much more magnified figure of a single Antherozoid as it appears when free, and in the act of moving through the water.

On the accompanying illustration are many examples of Spiral Springs, both natural and artificial. We will take these in their order.

The upper left-hand figure represents the “Buffer,” by which the carriages of railway trains are prevented from jarring against each other.

Perhaps some of my readers may be old enough to remember the days of the old railway carriages that were connected by short chains, and furnished with buffers that were merely padded. As the train started a separate jerk was given to every carriage by the tightening of the chains, and, as it stopped, all the carriages bumped against each other in a most unpleasant manner. Now, however, the buffers are furnished with powerful springs, and are pressed strongly against each other by means of screw-bolts, so that they form one continuous line.

In fact—and here is another analogy between Art and Nature—a train, when properly made up, bears a close resemblance to a human spine, the carriages being analogous to the vertebræ, and the spring buffers to the elastic cartilages between the vertebræ.

Nowadays, owing to this arrangement, the whole train moves together, and can be started and stopped so gently that the passengers are hardly aware of movement or stoppage. For example, one of my friends was in a train which came into collision with some obstacle. The carriages in front were dashed to pieces, and several of the passengers killed. His carriage, however, which was nearly at the end of the train, and had the benefit of all the springs, was hardly shaken, and the inmates did not know for some little time that an accident had occurred.

Below the buffer is a Wheel Spring, made exactly on the same principle, but set perpendicularly instead of horizontally.

The two figures beneath the wheel spring represent an object very familiar to us, namely, a Spring Solitaire, one figure showing it as open, and the other as closed. In this article the clasp is held in its place by a spring, and is only released by pressure.

Below the solitaire is a very prosaic application of the Spiral Spring, namely, that by which a house-bell is kept in vibration after the force of the pull has ceased, and which renders the bell, as Dickens happily remarks, so greedy to ring after it has been pulled.

I made and employed a spring of a similar character in closing the door of my parrot’s cage. Polly is a wonderfully clever bird, and a capital talker. First, she had a cage with upright bars, two of which could be slid upwards by way of a door. She soon found out the trick of the bars, and used to escape, carefully replacing the bars afterwards.

When she was transferred to a metal cage, she discovered that the door slid upwards, and began at her old tricks. So I took a piece of galvanised iron wire, coiled it into a spiral spring, fastened one end to the upper part of the door, and the other by a hook to a staple at the bottom of the cage. Consequently, when Polly lifted the door, and loosened her grip for a fresh hold, the door closed itself again. So, after awhile, Polly gave up the door, and now never tries to open it.

Passing to the upper right-hand corner of the illustration, there is shown a portion of Moss as it appears when magnified, and discharging its spores. When they are ripe a vast number of little spiral springs are let loose, and shoot the sporules into the air.

Below the moss are four figures, which are, in fact, the same object differently magnified, and seen from different points of view. These peculiar organs are technically termed “cnidæ,” from a Greek word which signifies a nettle. The appropriateness of the name we shall presently see.

I have already mentioned that the tentacles of various marine animals are furnished with poison-cells. The object of these cells is to capture and kill the prey, and the mode of doing so is very remarkable.

On the right and left of the illustration are two such bodies, in which is seen a sort of elastic wire coiled spirally, apparently without regularity, but really possessing a most beautiful order. That on the left is the poison-cell of a Madrepore, and the other is the same organ in a Corynactis. No sooner is the tentacle touched than the poison-cells are mechanically acted upon. They are turned inside out, and the coiled spring darts forth with wonderful violence.

Slight as is the dart, so fine that it cannot be seen except with the aid of a tolerably powerful microscope, it is a terrible weapon. Although it is projected with sufficient force to bury itself to its base even through so tough an object as the human skin, it could inflict but little injury, and would, indeed, scarcely be felt. But it carries with it a most irritant poison, which is apparently contained in the little capsule. These cnidæ are very plentiful in the tentacles of the Stinging Jelly-fish, or Stanger, as it is often called, and are charged with a terrible poison.

As is the case with all such poisons, its effects differ according to the constitution of the being that is poisoned. There are some persons, for example, who care no more for the sting of a bee than for the prick of a needle, and there are those whom a single bee-sting will bring almost to the gates of death. So with the tentacles of the Stinging Jelly-fish and those of the Portuguese Man-of-war, and there are persons who are scarcely affected with the sting of the scorpion.

So it is with nettles. When I was a boy at school it was thought necessary to wear an oak-leaf, or at least a portion of an oak-leaf, on the 29th of May, and all who did not possess this talisman might be flogged with nettles by those who did. As the school was situated in the north of England, where the oak puts forth its leaves late in the season, it was no easy matter to obtain a veritable oak-leaf, and we used to take any leaf that we could procure, and cut it round the edges into the similitude of a suitable oak-leaf.

The effect of the nettles upon the boys was most curiously diversified. Some cared nothing whatever for them; others suffered sharp but brief pangs; while others, of whom I was one, endured the most lancinating pain at the time, and for hours afterwards a hot, burning, fevered skin, and a heavy, dull ache, accompanied by throbbings of the brain so violent that it appeared as if the head would burst asunder at every heart-beat.

The fact of this inequality has been throughout life a valuable lesson to me, i.e. that a punishment which will nearly, if not quite, kill one man, will be no punishment at all to another.

Of course I cannot answer for the effects of these very minute cnidæ upon others, but I can state that they nearly killed me, and that if I had been forced to swim another hundred yards, I should have collapsed, sunk, and had a coroner’s jury return a verdict of “Found drowned in consequence of cramp.”

On me the effects were as follows:—First a slight, and then a severe, tingling on the parts which had been struck. Then sharp, darting pangs. Then a sudden shock as if a bullet had passed through the breast from one side to the other. Consequent collapse, and suspension of the office of both heart and lungs. I once had to walk nearly two miles after being stung by one of these dread animals, and how often I fell before reaching my lodgings I dare not say, but certainly once in every two hundred yards.

Even after partial recovery I should not have known my own face. It was that of an old and wearied man of seventy, grey, wrinkled, and withered; and many months elapsed before I felt myself sure that the weird-like bullet would not drive through my breast, and leave me lying on the ground gasping and speechless.

These dreaded tentacles can sting as fiercely when separated from the animal as when they are conjoined to it, as I can also testify from personal experience.

I have a natural alacrity in damaging myself, and there is scarcely a representative bone in the body that I have not fractured or dislocated, or both. Fortunately the cerebral vertebræ have hitherto escaped. I have broken the right leg, right arm, two ribs, and right collar-bone; dislocated the right ankle, and smashed nearly every bone of the right hand. At present, the damage to the left side is restricted to two ribs; and I hope that the Genius of Ossifraction may now be content with his work.

But I equally seem to have a natural affinity for the tentacles of the Stangers, which deliver their envenomed darts just as fiercely when they are separated from the Medusa as when they are connected with it.

A curious example of this fact befell me in the present year (1875). Seeing that there had been a steady southern gale, which made Lundy Island and Hartland and Baggy Points indiscernible, I dreaded my old foes, and, instead of bathing from the “Pebble Ridge,” took to the great “Nassau” Baths at Westward Ho. I sadly missed the roll of the waves, and the placid rapture of lying with outspread arms as the vast Atlantic billows came rolling in, flinging up the great grey boulders as if they were corks, and letting them roll down the ridge again with a thundering, and yet soothing, sound. Three miles or more inland may the thunder of the Pebble Ridge be heard; and at night, even though a storm be raging, tearing the leaves off the trees in whirling showers, flinging great branches into the air like ostrich plumes, and howling so that one person can hardly hear another speak, the dull, low, continuous thunder of the Pebble Ridge is heard over all. I have often remained awake at Bideford, simply on account of the deep roar of the Pebble Ridge, as the rising tide rolled its vast waves along the coast from Baggy Point, through Westward Ho and Clovelly, to Hartland.

When there is a heavy sea, the “undertow” of these waves is so great that even had no such things as Stangers existed, I should not have ventured upon the Pebble Ridge. One of my friends, a strong swimmer, was nearly drowned off that ridge by the undertow; and not long before I visited Westward Ho a promising young man lost his life within a few yards of that treacherous shore.

Much against my will, I went to the new bath, which is always supplied with a running current of sea-water; and I had hardly swum the length of the bath before I felt the familiar nettle-like sting in my foot. Fortunately it was only caused by a small fragment of a Stanger’s tentacle, which had been severed from the animal and pumped into the bath, and no harm ensued.