Nature's Teachings

A good example of this property may be found in a lighted stick, which, if rapidly whirled round, appears to form a continuous circle of fire. The reason of this is, that the impression made on the retina by the fiery point does not cease until the stick has again come round in its course.

Then there are those well-known chromatic tops, in which are inserted pieces of bent wire. When the top is spun these pieces of wire assume exactly the appearance of transparent jugs, vases, glasses, and similar articles. A very pretty illustration of this principle is given by a little machine, which is made to revolve rapidly by means of a multiplying wheel.

Upon its surface are fixed little pins, with polished globular steel heads, and, when the handle is turned, these heads form the most beautiful and intricate figures with exact accuracy.

Another toy, called the Thaumatrope, or Wonder-turner, is equally ingenious and beautiful, and is sufficiently simple to be made by any one with a slight knowledge of drawing. A disc of white cardboard is cut, and upon each side of it is portrayed some object. If the disc be caused to revolve rapidly, these two subjects will be seen at the same time, the image of each being held on the retina long enough to allow the other to take its place.

Some very beautiful combinations may be made by means of this instrument. For example, a horse may be on one side, and a man on the other, and, by spinning the disc, the man will be seen mounted on the horse. Then we may have a boat on one side, and a rower with his oars on the other. Similarly a mouse can be put into a trap, or a bird into a cage.

The reader must remember that these subjects must be drawn as if they were upside down with regard to each other, so that the man who is to ride the horse is drawn as if he were standing on his head, and the mouse which is to enter the trap looks as if it were lying on its back.

The most simple manner of spinning the disc is by means of two threads, each being inserted near the edge of the disc, and exactly opposite each other.

A very ingenious modification of the Thaumatrope is made by inserting at one side of the disc two strings, of which one is elastic. It is evident, then, that by lengthening or shortening the elastic string, the axis can be changed, and the objects on the opposite sides placed in positions relatively different from each other. Thus the jockey may be made to jump on and off his horse, the bird to go in and out of its cage, the mouse to enter the trap, and so on. This simple invention allows of infinite combinations, so that a tree may be made to sprout, a man to move his limbs, and a bird to flap its wings. It was invented, I believe, by Dr. Paris, author of “Philosophy in Sport made Science in Earnest.”

On the right hand of the illustration are seen three figures, each representing a means of obtaining an ocular delusion through the principle of which we are now treating.

The lower figure is called the Zoetrope, or Wheel of Life. As the reader may see, it consists of a hollow cylinder, revolving on a centre, and having within it a series of figures. When the wheel revolves, and the figures are viewed through the slits, each figure seems to be in lifelike motion, whence the name of Zoetrope. In the present case the figures are those of boys jumping over posts.

The mode in which this effect is produced is as follows:—Suppose that a boy were really to jump over a post, he would go through a series of motions, and his body be placed in a certain series of positions, before he cleared the post. Supposing, then, that several points were chosen in his course, and his body drawn as it would appear at these points, and the drawings placed in their proper order in the Zoetrope, it is evident that the figures must appear in movement. Before the retina loses the image of the boy standing in front of the post, it takes in that of the boy stooping, with his hands on the top of the post, and so on until he has reached the ground on the opposite side.

Another mode of producing the same effect, called the Phantasmascope, is seen above the zoetrope. In this case the images are placed on the inside of the disc, which is held opposite a mirror, and the figures viewed through the slits.

The last of these figures is the rather complicated one, like the back of an “engine-turned” watch. This is called the Chromatrope, or Wheel of Colour, and is always a favourite object in a magic lantern. It consists of two circular plates of glass, one upon the other, and painted in variously coloured curved lines, as seen in the illustration. When the image is thrown upon a screen, and the glass plates turned in opposite directions, a most singular and beautiful effect is produced. The lines, unless the eye follows them very closely, disappear, and torrents of coloured spots seem to pour from the centre to the circumference, or vice versâ, according to the direction in which the glass wheels are turned. So perfect is the illusion, that it is almost impossible to believe that the movement is only circular, and not spiral.

Now we will pass from Art to Nature. The figure on the left hand of the same illustration represents part of one of the Wheel Animalcules, so called because they look exactly as if the fore-part of their bodies were furnished with two delicate wheels, running rapidly round, and evidently moving or stopping at the pleasure of the owner.

Soon after the powers of the microscope became known, these Wheel-bearers were discovered, and for a long time they were thought to have a pair of veritable revolving wheels upon their heads. They were naturally held in high estimation, as, although almost every kind of lever can be found in the animal world, a revolving wheel had never been seen. However, as the defining powers of the microscope improved, the so-called wheels were found not to be wheels at all, but stationary organs, and that their apparent revolution was nothing but an optical delusion.

The wheels are, in fact, two discs, around the edges of which are set certain hair-like appendages, called “cilia,” from a Latin word signifying the eyelashes. Each of the cilia has an independent motion of its own, and, as they bend in rapid and regular succession, they produce an effect on the eye similar to that of a revolving body. As for the animal itself, they produce a double effect, either acting as paddles, and forcing the animal through the water, or, when it is affixed to some object, causing a current which drives into its mouth the minute beings on which it feeds.

The particular species of Wheel-hearer whose mouth is here shown is called scientifically Limnias ceratophylli. It derives the latter name from the fact that it is mostly found on the submerged stems and leaves of the Hornwort (Ceratophyllum), which is very common in ponds and slow streams. The creature is, however, to be found on the water-growing plants, and Mr. Gosse, in his “Evenings with the Microscope,” gives a very full and graphic account of itself and its habits.

He specially mentions the use of the wheels, and, by dissolving a little carmine in the water, had the pleasure of seeing the coloured granules swept into the mouth by the current caused by the cilia through the jaws, and so into the stomach.

USEFUL ARTS

CHAPTER I.
PRIMITIVE MAN AND HIS NEEDS.—EARTHENWARE.—BALL-AND-SOCKET JOINT.—TOGGLE OR KNEE JOINT

Contrast between Savagery and Civilisation.—Manufacture of Weapons.—Earthenware of Art.—Sun-baked Vessels.—Earthenware of Nature.—Nest of Pied Grallina.—Analogy with the Babylonish Brick.—Nest of the Oven-bird.—A partitioned Vessel.—Necked earthenware Vessels.—Nests of Eumenes, Trypoxylon, and Pelopœus.—Proof of Reason in Insects.—The Ball-and-socket Joint.—“Bull’s-eye” of Microscope.—The human Thigh-bone.—Vertebræ of the Serpents and their Structure.—The Sea-urchin and its Spines.—Legs and Antennæ of Insects.—The Toggle or Knee Joint, and its Use in the Arts.—The hand Printing-press and the Toggle-joint.—The human Leg and Arm.—Power of the natural Toggle-joint.—Fencing and Boxing.—Heads of Carriages.—“Bowsing” of Ropes.—Leaf-rolling Caterpillars.

IN the primitive ages of Man the aids to civilisation were very few and very rude. Some of them, especially those which relate to hunting and war, have already been mentioned, and we now have to deal with some of those which bear upon domestic life.

Here we are in some little difficulty, for it is not very easy to draw the line where domestic life begins, or the mode in which it shall be defined. We may at all events connect domestic life with a residence of some sort, and may, in consequence, neglect all such primitive savages as need no domestic implements.

Such, for example, are the few surviving Bosjesmans of Southern Africa, not one of whom ever made a tool or an implement, or looked beyond the present day. The genuine Bosjesman can make a bow and poison his arrows, and he can light a fire; but there his civilisation ends. He cannot look beyond the present hour, he has not the faintest notion of making a provision for the future, nor did his wildest imagination ever compass the idea of a pot or a pan.

He kills his prey, and, if hunger be very pressing, he will eat it at once without waiting for the tedious ceremony of cooking; or at the best will just throw the meat upon the fire, tear it to pieces with his teeth, and swallow it when it is nothing but a mass of bleeding flesh, charred on the outside, and absolutely raw within. The Bosjesman has not even a tent which he can call his own, any bush or hole in the ground answering for a house as long as he wants it, and then being exchanged for another.

As far as we know, the only trace of civilisation in the Bosjesman is his manufacture of weapons, and even his bow and arrows are of the rudest and clumsiest forms. Nor is it likely that he will ever advance any further; for, as is the wont of all savage tribes, he is disappearing fast before the presence of superior races, and will shortly be as extinct as the Tasmanians, the last of whom died only a few years ago.

Earthenware

The advent of real civilisation seems to depend largely upon the construction, not of weapons, but utensils, and the most useful of these are intended either for the preparation or the preservation of food. That such vessels should be made of earth is evident enough, and it is worthy of remark that the rude earthenware pot of the naked savage and the delicate china of Sèvres should both be products of the earth, and yet be examples of the opposite ends of civilisation.

The most primitive earthenware vessels were simply baked in the rays of the sun, the use of fire for hardening them being of later date. Rude and simple as they are, some of these vessels possess tolerable strength, and can answer every purpose for which they are intended. I possess several pots made by the aborigines of the Essequibo district. They are very thick and heavy in proportion to their dimensions, and are still so fragile that I have been obliged to bind them with string whenever they are moved.

Simple as they are, however, they are pleasing to the eye, chiefly, I presume, because they are made for a definite office, and fulfil it, and have no pretence about them. Then, as they are moulded by hand alone, without any assistance from machinery of any kind, even a wheel, the individuality of the maker is stamped upon them, and no two are exactly alike either in form, colour, or ornament. A couple of these rude vases are to be seen on the right hand of the accompanying illustration.

On the left hand of the same illustration are shown two examples of earthenware vessels made by birds, which are nearly, if not quite, as good as those made by the hands of civilised man.

The upper figure represents the nest of the Pied Grallina (Grallina Australis), a bird which, as its specific name implies, is a native of Australia.

This nest is formed chiefly of clay, but a quantity of dried grass is always mixed with it, and serves to bind it together. If one of these nests be broken up, and compared with the bricks of which ancient Babylon was built, it will be found that they are almost identical in material, and that both are merely baked in the sun. In form it so closely resembles an Essequibo jar in my possession, that if it were removed from the branch, and similarly coloured, it would not be easy to distinguish the one from the other.

Below this is the nest of the Oven-bird of South America (Furnarius fuliginosus), a bird allied to our common creeper. The drawing was taken from a specimen in the British Museum.

Like the nest of the Grallina, it is placed upon some horizontal bough, and fixed so firmly that it cannot fall except by being broken to pieces. Not being afraid of man, the Oven-bird often chooses a beam in some outhouse for a resting-place, and has been known to build even on the top of palings. As may be seen by reference to the illustration, the nest is a very conspicuous one, and concealment is almost impossible.

As in the Grallina nest, the material is remarkably hard and firm, as indeed is necessary, to allow it to withstand the effects of the rain-torrents which fall during the wet seasons of the year.

There is a curious analogy in this nest with many articles of earthenware. Not only among ourselves, but among uncivilised races, earthenware vessels are constructed with partitions, so as to divide one portion from another. If one of these nests be cut open, it will be found to have a sort of partition wall across the interior, rising nearly to the top of the dome, and so dividing it into two parts. The wall also answers another purpose—i.e. that of strengthening the entire structure. Within the inner chamber is the real nest, which is lined with a thick layer of feathers, the outer chamber being bare, and, as it is thought, being occupied by the male.

We now come to pottery of a more elaborate shape. Both in the Grallina nest and the earthen pot of the Essequibo Indian we have a vessel with a mouth nearly as wide as its greatest diameter, and with a lip which is very slightly turned over. There are, however, many varieties of pottery in which the neck is narrow and long, and the lip is boldly formed. Some examples of this form are given on the right hand of the accompanying illustration.

On the left hand are shown some nests of a solitary wasp belonging to the genus Eumenes. It is a British insect, but seems to have been little noticed, except by professed entomologists.

It especially haunts heather, and affixes to the stems of the plant its little globular nests, which are made of mud, and shaped as seen in the illustration. Perhaps some of my readers may have seen the “Napier Coffee Machine,” which draws the coffee into a glass globe furnished with a short neck. The globe is shaped exactly like the nest of our Eumenes, and, when I first saw one, I could not remember why its shape was so familiar to me.

As is the case with the birds’ nests which have been mentioned, the mud of which the walls are built is of a most tenacious character, and, when dried in the sun, can resist the heaviest rain. The cells are intended as rearing-places for the young, only a single egg being placed in each cell, which is then stocked with small caterpillars by way of food.

There is a South American insect also belonging to the solitary wasps, and remarkable for building a round nest exactly similar in material, and nearly identical in shape, with that of the Eumenes. Its scientific title is Trypoxylon aurifrons. The nest of this insect has a much wider mouth than that of the Eumenes, and exactly resembles the upper left-hand jar in the illustration.

Another South American solitary wasp, belonging to the genus Pelopœus, makes nests of similar material, but nearly cylindrical in shape instead of globular. The nest is built up of successive rings of moistened and well-kneaded clay, exactly as human houses are built by bricklayers. Indeed, the process of making a Pelopœus’ nest has been happily compared to that of building a circular chimney.

I may as well mention here that the name Pelopœus is formed from a Greek word signifying mud, and that the entire word may be translated as “mud-worker.”

As a proof that these insects possess reason as well as instinct, Mr. Gosse mentions that one of them, instead of making her nest for herself, utilised an empty bottle, and, after storing it with spiders, stopped up the mouth with clay. Finding, after an absence of a few days, that the nest had been disturbed, she removed the spiders, inserted a fresh supply, and then closed the mouth as before.

Ball-and-socket Joint

We will now see how some of the most useful mechanical inventions have had their prototypes in Nature.

There is, for example, the well-known “Ball-and-socket joint,” without which many of our instruments, especially those devoted to optical purposes, would be impracticable.

The figure on the right hand of the illustration represents the “bull’s-eye” of my own microscope. It will be seen that there is a ball half sunk in a cup, so that it can be turned in any direction. In point of fact, the upper part of the ball is nearly concealed by another cup, but, in order to show the structure, the upper cup has been removed. Who was the inventor of the ball-and-socket joint I do not know, but I have little doubt that he must have had in his mind many natural examples of this joint, three of which are represented in the illustration.

On the left hand are seen the upper part of the human thigh-bone and that part of the hip-bone into which it fits.

The reader will see that at its upper end the bone takes rather a sharp turn, and is then modified into a ball. This ball fits into a corresponding socket, technically named the “acetabulum,” and is thereby endowed with freedom of motion in almost every direction. Generally we do not practise our limbs sufficiently to develop that full freedom, but those who have seen any good professional acrobats must have been struck with the wonderful mobility of which the human body is capable.

The socket is not a deep one, but dislocation of the hip is exceedingly rare, the bone being held in its place by three powers. The first is due to a short ligament, which, however, does not always exist, but, when it is present, is useful in retaining the bone in its place. Then there is the contractile power of the thigh muscles, which are always forcing the ball into the socket. Lastly, there is the pressure of the atmosphere, a force which is seldom taken into consideration, but which has great influence on many parts of the human frame. This part of the subject will be resumed when we come to treat of Atmospheric Pressure.

The arms are jointed to the shoulder-blades in a very similar manner, the upper arm-bone, or “humerus,” being furnished with a rounded end, and fitting into a cup-like cavity in the shoulder-blade, or “scapula.” This formation can easily be seen by separating the different bones of a shoulder of mutton.

At the bottom of the illustration are given two vertebræ of a snake, separated in order to show their structure. It will be seen that each joint has a ball in front and a socket behind, thus giving the creature that wonderful flexibility which is quite proverbial, and without which it could not seize its prey.

The following eloquent passage is taken from Professor Owen’s work entitled “The Skeleton and the Teeth:”—

“Serpents have been regarded as animals degraded from a higher type, but their whole organization, and especially their bony structure, demonstrate that their parts are as exquisitely adjusted to the form of their whole, and to their habits and sphere of life, as is the organization of any animal which we call superior to them.

“It is true that the serpent has no limbs, yet it can outclimb the monkey, outswim the fish, outleap the Jerboa, and, suddenly loosening the coils of its crouching spiral, it can spring into the air and seize the bird upon the wing: all these creatures have been observed to fall its prey.

“The serpent has neither hands nor talons, yet it can outwrestle the athlete, and crush the tiger in the embrace of its ponderous overlapping folds. Instead of licking up its food as it glides along, the serpent uplifts its crushed prey, and presents it, grasped in the death-coil as in hand, to its slimy, gaping mouth.

“It is truly wonderful to see the work of hands, feet, and fins performed by a modification of the vertebral column—by a multiplication of its segments with mobility of its ribs. But the vertebræ are especially modified, as we have seen, to compensate, by the strength of their numerous articulations, for the weakness of their manifold repetition, and the consequent elongation of the slender column.

“As serpents move chiefly on the surface of the earth, their danger is greatest from pressure and blows from above; all the joints are fashioned accordingly to resist yielding, and sustain pressure in a vertical direction; there is no natural undulation of the body upwards and downwards—it is permitted only from side to side. So closely and compactly do the ten pairs of joints between each of the two hundred or three hundred vertebræ fit together, that even in the relaxed and dead state the body cannot be twisted except in a series of side coils.”

The upper right-hand figure represents a portion of the shell of an Echinus, or Sea-urchin, together with two of the spikes.

The reader will remember that in the description of the Heart-urchin, and the mode in which it dug its way into the sand, the peculiar mobility of the spines was mentioned. How that mobility is produced we shall now see.

If a living Sea-urchin can be procured, and placed in a glass vessel filled with sea-water, it will at once be seen that its surface is thickly covered with spines. In some species these spines are as thick as ordinary drawing pencils; but in most of those which are found on our shores they are very slight, and scarcely longer than darning-needles. They are in almost perpetual motion, and generally have a sort of revolving movement, the base being the pivot.

Now, if we take a dried shell of the Sea-urchin, we shall find that the spines will come off with a touch, and, indeed, to preserve one with all the spines complete is a most difficult business. Let us, therefore, pull one from its attachment, and examine its base. This will be found to be swollen into a cup-like form, as seen in the illustration; and, if we look at the spot whence it came, we shall see that there is a little, rounded, polished prominence, exactly fitting into the cup, just as the ball of the human thigh-bone fits into the acetabulum. It has also its ligament to keep it in its place, and its same set of muscles that move it, and is altogether a most wonderful piece of mechanism. There are in some species of Echinus about four thousand of these spines.

The legs of an insect afford excellent examples of the ball-and-socket principle, the socket being on the body, and the ball on the base of the leg. Some of our largest insects—such, for example, as the common Stag-beetle—exhibit this principle very well. I have now before me a Stag-beetle which has been dead for many years, and is quite dry and hard. Yet I can rotate the legs almost as freely as if the beetle had been just killed, so easily do the joints work. Even the antennæ, which are affixed to the head by a similar joint, move about by their own weight on merely changing the position of the insect.

These are only a few of the many natural examples of the Ball-and-socket joint, but they are sufficient for our purpose.

The Toggle or Knee Joint

Another most useful invention now comes before us, called the Toggle-joint, or Knee-joint, the latter name being given to it on account of its manifest resemblance to the action of the human knee.

This joint is shown in the illustration. It consists of two levers, jointed together at one end, and having the other ends jointed to the objects which are to be pressed asunder. It will be seen that if the centre of the Toggle be pushed or pulled in the direction of the arrow, so as to straighten the levers, the amount of pressure upon them is enormous. Such an apparatus as this combines simplicity and power in a wonderful manner, and is greatly used in machinery, especially in presses, where the force is required to be great, but not of long duration.

An ordinary two-foot rule, when bent, affords a good example of the Toggle-joint, and will exert a wonderful amount of force.

The illustration represents one of the common printing-presses that are worked by hand. When the workman draws the handle horizontally, he causes the two portions of the Toggle to approach a straight line. The upper half of the Toggle being jointed to the fixed beam above, and the other half to the movable plate or “platen” below, it is evident that the latter will be pressed downwards with enormous force. Indeed, so great is the power of this instrument, that a man of moderate strength can exert a pressure of many tons.

We now proceed from Art to Nature, and take first the human knee, being the joint from which this piece of mechanism has derived one of its names.

If the reader will look at the figure of the fencers, he will see that the arm and leg are both Toggle-joints. In the one who is standing on the defence they are bent, and in the other, who has just made a longe, the Toggles of the right arm and left leg are straightened. It is by the straightening of these joints, and not by the action of stabbing, that the rapidity and force of a thrust are achieved.

It is just the same in boxing. No one who has the least knowledge of sparring strikes a round-handed blow, for, putting aside the ease with which it is parried or avoided, it has scarcely any force in it. When a boxer hits “straight from the shoulder,” he not only straightens the Toggle-joint of his left arm, but that of his right knee also, so that the force of the blow comes quite as much from the leg as the arm.

It is by the right use of this joint that a small man, provided he be an expert boxer, will easily conquer an ignorant opponent who far surpasses him in size and weight. I have seen in a sparring-match a man not only knocked down, but fairly lifted off his feet, by a blow from a smaller opponent. The blow took effect under the chin, and, as the boxer hit exactly the right moment in straightening both limbs, a very great force was exerted with little apparent effort. I do not know which of the two combatants was the more astonished, the one to find himself on his back without exactly knowing how he got there, and the other to see his antagonist prostrate without exactly knowing how the thing was done.

The jointed apparatus by which the heads of carriages are raised or lowered is a good example of the Toggle, and exemplifies the force which a comparatively slight piece of machinery can exercise.

Another form of the Toggle-joint is the process called by sailors “bowsing” of rope. If a rope be fastened at both ends, and then pulled in the middle, the ends are drawn forcibly towards each other. This plan is mostly adopted in getting up sails. When a sail, say the mainsail of a cutter, has to be hoisted as far as it will go, the last few inches are always very obstinate. The word is then given to “bowse.” The rope, or haulyard, is no longer pulled at the end, but a turn is taken round the cleat, so that it does not give way. The rope is then forcibly pulled away from the mast, when up goes the gaff a little higher. In this way, by repeated bowsings, the gaff is coaxed, so to speak, up the mast, and forced into its place.

Some of the leaf-rolling caterpillars act in a similar manner, by alternately bowsing and shortening their lines. As, however, their mode of working will be described under another heading, we will say no more of them at present.