Means and Appliances.

IN this chapter we will take some miscellaneous appliances of force both in Art and Nature.

In the accompanying illustration is shown the Cassava Press of Southern America, a most effective and simple instrument for extracting the juices of the root. These juices are poisonous when raw, but, when properly boiled and cooked, they make an excellent sauce.

The press in question is an elastic tube made of flat strips of cane woven together exactly like the “Siamese Link,” which will be presently described. The cassava root, after having been scraped until it resembles horseradish, is forced into the press until it can hold no more. The result is, that the tube is shortened and thickened, being widest in the middle.

It is then hung by its upper loop to the horizontal beam of a hut. A long pole is passed through the lower loop, the short end is placed under a projecting peg on the upright post of the house, and a heavy weight attached to the longer end. A powerful leverage is thus obtained, the tube is forcibly shortened, and the juice exudes through the apertures of the woven cane.

When it begins to run slowly, a woman seats herself at the end of the pole, so as to increase its weight. I must mention here that in the illustration the press is too near the middle of the pole. This is because the exigences of our page do not admit of the requisite length. But if the reader will kindly assume the end to which the stone is attached to be three or four times longer, he will have an idea of the great power which is exerted upon the cassava.

On the left hand of the illustration is the same cassava press as seen when empty, and both figures, as well as that of the pot for receiving the juice, are taken from specimens in my collection.

On the right hand of the following illustration is the Siamese Link, which caused such a sensation when it first came out.

A finger is inserted at each end, and, when the owner attempts to withdraw them, the Link contracts, and the harder the pull, the tighter is the hold. If the fourth instead of the first finger be employed, the hold of the Link is exceedingly strong.

The only mode of release is by pushing the fingers together, when the Link will relax. It should then be held by the remaining fingers of one hand, so that it shall not contract again, and the finger of the other hand comes out at once.

An ingenious robbery was once committed by means of the Siamese Link. A man of good address struck up an acquaintance with a jeweller. One day he produced a Siamese Link, and challenged him to get his fingers out when once they were in. So the jeweller was told to put his hands behind his back, and push his little fingers as far in as he could.

This he did, when the treacherous friend made a clean sweep of all the rings, brooches, ear-rings, and such jewellery as was within his reach, while the unfortunate jeweller was vainly tugging at the Link. This only occupied a few seconds for a practised hand, and the thief quietly opened the door, shut it, and was lost in the passing crowd before the jeweller could recover from his surprise.

On the left of the same illustration is a view of the muscles of the human leg, which, as the reader will see, are curiously like the distended cassava press. Although the mode of applying the force differs, the principle is the same.

In the latter case an external force is applied to the press, but in the latter an internal, or rather a central, force is applied to the bones. It is evident that if a similar process were carried on with the cassava press, and the central portion forcibly distended, the supports at either end would be drawn powerfully towards each other. Substitute the muscle for the press, and the bones for the poles, and this is muscular action.

Here we have a diagram which speaks for itself, as far as muscular action is concerned, but there is another point to which we shall presently pass.

The muscle of the arm is seen running along the bone, passing over the elbow, where it is held down by a tendinous band, and, by its contraction, enabling the arm to be bent so as to uphold a considerable weight. The mechanical analogy between this arrangement and the common Steelyard is too evident to need any explanation except inspection of the diagram.

There is, however, another point which is worthy of consideration. The muscle does not proceed at once from the shoulder to the wrist, but passes under the tendinous band above mentioned, and so produces a change of direction when the arm is bent.

There is a more complicated arrangement of a similar character in the human hand, a diagram of which is given in the left-hand figure of the accompanying illustration.

The fingers are, of course, moved by a set of tendons, and the muscles, from which these tendons spring, are attached to the fore-arm (I purposely omit the scientific titles, though they would be much easier to write). Any of my readers can prove this for themselves.

Let him first grasp the upper arm firmly, and bend the limbs, and he will at once find that the swelling of the muscle shows the source of power.

Then let him do the same, but grasp the fore-arm, and he will find that the muscles are quiescent, showing that the former set of muscles belong to the entire arm, and not to the fingers, while the muscles of the lower arm have nothing to do with the bending of that limb.

Now let him grasp the fore-arm, and open and close the fingers, and he will feel a whole set of muscles rise, and swell and harden under his grasp. Next let him bend his hand inwards, and he will find that the fingers work perfectly well, though the direction of force is changed.

This is owing to a band of tendons passing across the wrist, under which the finger-tendons play. The course of the tendons is marked in the illustration by leaving them white.

The wondrous structure of the human hand and its multitudinous tendons can only be appreciated by actual dissection, but an idea of their variety and use may be obtained by watching the hands of a skilful pianoforte-player. This struck me forcibly the first time that I ever heard Thalberg play.

While on the subject of tendons, I may mention a curious case. A journeyman carpenter missed a blow with his axe, and struck his left hand at the junction of the thumb and wrist. The important tendon was severed, and the inner muscles, having no counteracting force, dragged the thumb into the hollow of the hand.

To all appearance, the man could no longer earn a living as a carpenter. But he would not be discouraged, and while he was in hospital he borrowed a book, and studied the anatomy of the human hand. By means of this knowledge he constructed a sort of semi-glove, in which he introduced pieces of watch-spring, that supplied the place of the lost tendon.

Not content with this, he studied Euclid for the purposes of his trade, so as to get the most possible out of a piece of wood of given dimensions, and be able to go straight to his mark by a problem, instead of doing it slowly and clumsily with a two-foot rule and a pair of compasses. When I saw him last he was a master carpenter in a large and increasing business.

Man has unconsciously imitated Nature in the invention of the Pulley, whereby the direction of force may be altered almost at will. In this case the cord takes the part of the working tendon, and the Pulley of the fixed tendinous crossbar. There is much matter of interest in the tendons, but, as our space is fast waning, I must resist the temptation of describing them.

In all machinery one of the chief objects of the machinist is to reduce friction as much as possible. He makes all the joints as smooth as tools can polish, and always introduces oil or some lubricating substance into the joints. Otherwise the engine rattles with a noise proportionate to its power, and wastes its force on the friction.

In my childish days a steam-engine of any kind used to rattle so loudly that conversation was almost impossible. Now they are made with such perfection, that the vast engines in use at the pumping stations of the metropolitan drainage are almost absolutely silent.

There is the enormous hall, filled with gigantic beams and rods, and cranks, and wheels. A single man turns a little handle, and the whole machinery starts into life. Beams rock, cranks and wheels revolve, rods slide up and down, and all in a silence which is nearly appalling in its manifestation of unassuming strength. Indeed, many a hand sewing machine makes far more noise than one of those giant engines, and all because in the latter friction is avoided as far as possible, every screw is well braced up, and every joint is kept well lubricated.

Here I may observe that few sewing machines get fair play. They rattle, they squeak, they become stiffer daily, they snap the thread, and then decline work altogether. And in almost every case this is done by neglect on the part of the owner, who does not lubricate every point of the machine which works upon another.

Ladies especially are very careless in this respect, and will mostly omit three or four of the oiling points. They might just as well omit them all, as a single unoiled point will disarrange the harmonious motion of the whole machine. I have often been called in as surgeon in such cases, and have almost invariably been able to point to several spots which needed oil, and did not get it. Sometimes, out of false economy, an inferior oil is used, which speedily clogs and hardens, and stops all movement. In such a case the best remedy is to apply paraffine liberally, and use it for a quarter of an hour or so. It will soon dissolve the clogged oil, which may be worked out by turning the handle or crank of the machine.

Of course the best remedy is to take the machine to pieces, polish the joints, lubricate them, and put it together again. But this is a perilous process, and an amateur, if he tries it, will generally find himself with half-a-dozen pieces for which he can find no place. Paraffine will answer every purpose, and I have released many a stiffened machine by its use.

Then some people leave their machines untouched for days, or even weeks, and then wonder that they work stiffly. Every day the machine should he worked, if only for a few seconds, and then it will seldom stiffen. It is just the same with steamers. When they are in harbour, though the fires be out, and they are not meant to move for weeks, the engines are always turned round at least once daily.

Both these rules hold good in the animal kingdom.

To every joint there are attached certain glands that supply a kind of oily substance technically named “synovia,” which acts exactly the same part as the oil or grease of machinery. If these glands do not do their duty, and the supply of synovia be defective, the joints become stiff, painful, and crackle when they are moved.

Then, exactly as the joints of a machine become stiff from non-usage, so do those of a human being. We will take, for example, the Indian Fakirs who vow that they will not move some limb from a definite posture. At first the exertion is trying and painful, but by degrees the disused joints lose their faculty of motion, and, even if their owner wished to move a limb, he could not do it.

The right-hand figure of the illustration represents the lubrication of an ordinary sewing machine, and the left-hand figure is a section of the human knee-joint, showing the gland which supplies the synovia.

Perhaps some of my readers may think that such a subject as the “Lazy-tongs” is too trivial for a work which deals, however lightly, with science. But there may be some who know the inestimable benefit of Lazy-tongs under certain conditions.

There are many cases where a severe injury has occurred, or where rheumatism has fixed its tiger-claws in the joints, so that movement is all but impossible. There may be no one in the room to help the invalid, and even to stretch the arm over the table is as impossible as to jump over the house.

Then it is that the real value of the Lazy-tongs becomes manifested, and that it shows itself in the light of a supplementary limb. With a mere movement of the fingers it can be stretched across any table which is likely to be placed before an invalid, and seize the required object by the tongs at the further end.

The only drawback to its use is, that the instrument cannot be shortened without opening the tongs. But, if some plan could be devised whereby the tongs could retain their hold under those conditions, the instrument would be a perfect one.

Exactly such a Lazy-tongs we have in Nature, in the well-known “mask of the larva and pupa of the Dragon-fly.” It is called a mask because, when closed, it covers the face.

It chiefly consists of two flat, horny plates, hinged in each other like a carpenter’s two-foot rule, and being capable of extension to a considerable length. The end is widened, and furnished with two jaws, which take the part of the tongs in the instrument above described.

This curious apparatus is used for the purpose of securing prey.

I have kept many of these creatures, and watched their mode of feeding. As has already been mentioned, they have two modes of progression, i.e. walking by means of legs like those of ordinary insects; and driving themselves along by ejecting water from the tail, on the principle of the rocket. As far as I have seen, the latter mode is always used in taking prey. The Dragon-fly larva always lives at the bottom of the water, though it can force itself to the surface if needful. And, like the dreaded ground-shark, it seizes its prey from beneath.

Its favourite food is the larva of the whirlwig-beetle, a fat white grub, with a number of white, soft, feathery gills fringing its sides. In order to produce a current of air over these gills, the larva wriggles itself up to a height of several inches, and then sinks slowly down, with the white gills floating on either side.

Should a Dragon-fly larva be near, it sees the grub ascending, glides quietly under it without using its legs so as to cause alarm, waits for it to sink, darts out the mask, seizes it in the jaws, drags it to its mouth, and the grub is seen no more. So voracious are these larvÆ, that, if only two are kept in the same vessel, one is sure to devour the other.

Another good example of the Lazy-tongs is the Proboscis of the common House-fly. We have all seen these insects alight near sugar, or any other tempting food, unfold the proboscis, pour a drop of liquid in the sugar, dissolve it, suck it up, and then shut up the proboscis as if by hinges.

Another labour-saving machine is the Apple-parer, a comparatively modern invention. The principle is, that a knife is pressed lightly by a spring against a revolving apple, and set at such an angle that nothing but the outside peel can be removed. Where large numbers of apples have to be pared, as in making preserves or in hotels, this is a most useful invention.

When I first saw it at work, the operation seemed familiar to me, but I could not at first remember the parallel. At last it flashed across me that a Squirrel eating a nut was the natural parallel of the Paring Machine.

After splitting the shell and extracting the kernel, the Squirrel takes the latter between its fore-paws, presses it against its upper incisor teeth, and makes it revolve rapidly. In a second or two the kernel is perfectly peeled, and is then eaten.

In this case the incisor teeth of the Squirrel take the part of the knife, the muscles of the leg that of the spring, and the sharp edges of the upper teeth that of the knife. The structure of the Rodent teeth has already been explained in page 233.

The wonderful effects of water in breaking up the hardest rock have already been described. We will now proceed to another branch of the same subject.

Perhaps some of my readers may have wandered along our rocky coasts, and have seen how large masses of rock are continually detaching themselves, though they are so hard that a cold chisel is needed to make any impression upon them.

Then they fall into the sea, and are rolled backwards and forwards until they become smoothed and rounded, and are called pebbles, while the portion that is rubbed off them is called sand. The phenomenon is well shown in the wonderful Pebble Ridge of North Devon.

The real agent is ice.

We all know that, when water freezes, it expands considerably. This accounts for two phenomena.

First, as it expands, it becomes lighter than water, and consequently floats on the surface.

Next, there are few of us who have not seen water-bottles cracked by the freezing of the water. The most common, and perhaps the most unpleasant, example of this propensity is the bursting of water-pipes in the winter, followed by a flooding of the house when the thaw comes.

This is caused by the expansion of the frozen water, which will burst not only a thin leaden tube, but a stout iron vessel. Care should therefore be taken, at the beginning of winter, to cover up all exposed portions of leaden pipes, and there will then be no danger. There was one pipe in my house that was always bursting, but after I covered it with two or three layers of carpet placed loosely over each other, so as to entangle the air and form a non-conductor, the pipe has never frozen, and the water supply has been uninterrupted by the severest frosts.

I am told that a still better plan exists, especially in places where the pipes cannot be thoroughly protected by external wrappings. Let six inches or so of the leaden pipe be removed, and its place supplied by a vulcanised india-rubber tube.

The ice must expand somewhere, and chooses the spot where least resistance is offered to it. Consequently, it expands in the india-rubber tube, but does not break it, and, when the thaw comes, there is no overflow of water.

Man utilises this power of ice in stone-splitting. Instead of taking the trouble to cut the stone by manual labour, the workmen bore a series of holes, fill them with water, insert tightly a wooden plug to prevent the ice, when formed, from oozing out of the holes, and leave the rest for the frost to do.

A like effect is produced in the warm weather by substituting similar plugs, but quite dry, having been baked for hours in an oven, for the purpose of driving out every particle of moisture. These plugs are hammered into the holes as deeply as they will go, and there left. Even if there be no rain, the nightly dews make their way into the pores of the dry wood, and cause it to swell with such irresistible force that the stone is split with scarcely any manual labour on the part of the workmen.

Yet another plan for cutting hard stones. Some of my readers may be aware that a singularly ingenious instrument has been invented for cutting boles in granite and other hard rocks. It is called the Diamond Drill, because its tip is armed with uncut diamonds.

It is necessary that the diamond should not be cut, as the natural edges are needed. A glazier’s diamond, for example, is always set as it came out of the mine. The stories that are told about cutting out panes of glass with a diamond ring are all absurd. A diamond, when it has once passed through the hands of the jeweller, cannot cut glass. It can scratch glass, but not one whit better than a flake of ordinary flint.

It is found that the Diamond Drill works with wondrous rapidity, cutting away the stone with ease, and suffering scarcely any damage itself. The tube to the end of which the diamonds are fixed is generally made in telescopic fashion, so as to allow it to penetrate deeply into the rock, without the necessity of shifting the machine by which it is turned. I need hardly say that its rate of speed is very great indeed.

Our old friend, the Gad-fly, again affords an example of a parallel.

The ovipositor is tubular, telescopic, and furnished at the top with five little hard, sharp, scaly knobs, which act the same part as the diamonds of the mining tool. Even the scoop-like shape of the tip, and the telescopic shaft, are almost identical in both instances.