Image unavailable: WHEEL ANIMALCULE. PHANTASMASCOPE. CHROMATROPE. ZOETROPE.WHEEL ANIMALCULE. PHANTASMASCOPE. CHROMATROPE. ZOETROPE.
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, likethe 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, orvice 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.
Nowwe 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 scientificallyLimnias 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.
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.
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 ofmaking 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.
Theadvent 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.
Onthe 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.
Image unavailable: NEST OF PIED GRALLINA. NEST OF OVEN-BIRD. PRIMITIVE EARTHENWARE.NEST OF PIED GRALLINA. NEST OF OVEN-BIRD. PRIMITIVE EARTHENWARE.
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.
Belowthis 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 horizontalbough, 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.
Wenow 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.
Onthe 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. Theglobe 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.
Image unavailable: NESTS OF EUMENES. ANCIENT NECKED POTTERY.NESTS OF EUMENES. ANCIENT NECKED POTTERY.
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 isTrypoxylon 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.
AnotherSouth 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 isformed 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.
Wewill 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.
Image unavailable: HIP-JOINT. SPINES OF SEA-URCHIN. VERTEBRÆ OF SNAKE. BALL-AND-SOCKET JOINT OF MICROSCOPE.HIP-JOINT. SPINES OF SEA-URCHIN. VERTEBRÆ OF SNAKE. BALL-AND-SOCKET JOINT OF MICROSCOPE.
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.
Onthe 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.
Atthe 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 exquisitelyadjusted 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.”
Theupper 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 thatits 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.
Thelegs 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.
Anothermost 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.
Image unavailable: STRAIGHTENED TOGGLES. FENCERS. BENT TOGGLES. PRINTING-PRESS.STRAIGHTENED TOGGLES. FENCERS. BENT TOGGLES. PRINTING-PRESS.
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.
Wenow 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 onewho 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.
Anotherform 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, whenup 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.
Importance of Leverage in Crushing Power.—Nut-crackers a Lever of the Second Order.—The Chaff-cutting and Tobacconists’ Machines.—Jaws of various Animals.—The Wolf-fish or Sea-wolf.—The Rolling-mill and its Action.—Gunpowder-mills and Granulating Machine.—The “Jacob’s Ladder.”—The Mangle and its various Adaptations.—The Grindstone.—Primitive Grindstones of the Savage Races.—The Kafirs and the Inhabitants of Palestine.—Ceasing of the Millstone.—“Facing” of Millstones.—Tusk of the Elephant and its Structure.—Its Facings always preserved.—Power of Self-renewal.—Pressure of Atmosphere.—The Napier Coffee Machine.—The Cupping Instrument.—The Pneumatic Peg.—The Magdeburg Hemispheres.—Plane Surfaces of Glass or Metal.—Suckers of the Cuttle-fish.—Foot of the Water-beetle.—The Limpet.—The Star-fish and its Mode of Progression.—The Sucking-fish and the Fables connected with it.—Its real Structure.—Modification of the Dorsal Fin.—The Gobies and Lump-fish.—The Gecko and Tree-frog.—The Lampern and the Medicinal Leech.—Seed Dibbles and Drills.—Labourers versus Machinery.—Natural Dibble of the Grasshopper.—The Daddy Long-legs.—Drills and Dibbles of the Ichneumon-flies.—A wonderful Specimen from Bogotá.—The Pelecinus and its Mode of laying Eggs.
Importance of Leverage in Crushing Power.—Nut-crackers a Lever of the Second Order.—The Chaff-cutting and Tobacconists’ Machines.—Jaws of various Animals.—The Wolf-fish or Sea-wolf.—The Rolling-mill and its Action.—Gunpowder-mills and Granulating Machine.—The “Jacob’s Ladder.”—The Mangle and its various Adaptations.—The Grindstone.—Primitive Grindstones of the Savage Races.—The Kafirs and the Inhabitants of Palestine.—Ceasing of the Millstone.—“Facing” of Millstones.—Tusk of the Elephant and its Structure.—Its Facings always preserved.—Power of Self-renewal.—Pressure of Atmosphere.—The Napier Coffee Machine.—The Cupping Instrument.—The Pneumatic Peg.—The Magdeburg Hemispheres.—Plane Surfaces of Glass or Metal.—Suckers of the Cuttle-fish.—Foot of the Water-beetle.—The Limpet.—The Star-fish and its Mode of Progression.—The Sucking-fish and the Fables connected with it.—Its real Structure.—Modification of the Dorsal Fin.—The Gobies and Lump-fish.—The Gecko and Tree-frog.—The Lampern and the Medicinal Leech.—Seed Dibbles and Drills.—Labourers versus Machinery.—Natural Dibble of the Grasshopper.—The Daddy Long-legs.—Drills and Dibbles of the Ichneumon-flies.—A wonderful Specimen from Bogotá.—The Pelecinus and its Mode of laying Eggs.
AS we are on the subject of leverage, we will take some examples of levers in Art and Nature, without, however, even attempting to exhaust the topic.
On the right hand of the illustration is shown a very familiar example of a lever, namely, nut-crackers, with a nut between them. This useful implement is simply an adaptation of levers of the second kind, the power being represented by the human hand, the weight by the nut, and the fulcrum being the joint of the instrument.
The common chaff-cutter, which is worked by hand, is another familiar example of this kind of lever, and so is the knife used by tobacconists in cutting cake Cavendish into threads,and by druggists for similar purposes. In these instruments the point of the knife is jointed to some fixed object, and becomes the fulcrum; the hand of the cutter supplies the power, and the weight is the object which is being cut. It will be seen that, by increasing the length of the handle, very great power can be obtained.
Image unavailable: JAWS OF WOLF-FISH. NUT-CRACKERS.JAWS OF WOLF-FISH. NUT-CRACKERS.
Exchanging the power for weight, we have in the common tongs, whether used for the coals or for sugar, a leverage of a similar character, the weight moving over a greater space than the power. A good example of this is to be found in the deltoid muscle of the human arm. The muscle, which furnishes the power, contracts about an inch, and, so doing, moves the hand over some forty inches of space. It has been well stated that if a man is able to hold in his hand, and with extended arm, a weight of twenty-five pounds, the muscle must be exerting a power of forty times as great,i.e.about a thousand pounds.
Thereis little doubt that, in such Crushing Instruments as have been mentioned, the idea has been taken from the jaws of sundry animals. We know, for example, that with ourselves, if we desire to crack a walnut or a filbert in our teeth, we always put it as far back as possible, so as to make the leverage as powerful as possible. No one would ever dream of cracking a nut with his front teeth, an act which would be verymuch like that of trying to break a piece of coal by pinching it with the tongs.
The left-hand figure of the illustration represents part of the jaws of the Wolf-fish, or Sea-wolf, as it is sometimes called, and a very wonderful crushing machine it is. The Sea-wolf (Anarrhicas lupus), sometimes called the Sea-cat, or Swine-fish, is tolerably common on our coasts, and, as it sometimes attains a length of seven feet, and is proportionately stout and muscular, the power of its bite may be estimated. The fish in question feeds chiefly on crustacea and hard-shelled molluscs, and is therefore furnished with an apparatus which can crush their shells. Extremes meet. The Sea-anemones, which are mere films of animal matter, and can be torn in pieces with the finger and thumb, can seize, swallow, and digest a crab or an oyster in spite of the thick and strong shells in which they are enclosed. So can the Sea-wolf, and fishes of a similar character. But nothing intermediate can touch them, and it is curious to reflect that such opposite means should produce a similar effect.
On reference to the illustration, the reader will see how exact is the parallel between the Nut-crackers and the Sea-wolf’s jaws, both being worked on the same principle, and both being furnished with a series of projecting points, which are used for the purpose of preventing the escape of the object which is to be crushed. The terrible grasping power of the crocodile, the dolphin, and other predacious creatures can be explained on the same principle.
Wenow come to another variation of the Crushing Machine,i.e.that in which the motion is constant, and not intermittent, as is the case with those machines which have just been mentioned.
Perhaps some of my readers may have visited those great iron-works in which huge masses of iron are rolled into plates of greater or less thickness, or are cut up into strips as easily as if they were butter.
The mechanism is in its principle simple enough. The cylindrical rollers are placed nearly in contact, and forcedtowards each other by mechanical means, such as levers, screws, or springs, or all three combined. These cylinders revolve in opposite directions, and, if any object be placed between them, they draw it through them, and present it on the other side in a flattened condition.
Image unavailable: JAWS OF SKATE. CRUSHING-MILL AND ROLLER.JAWS OF SKATE. CRUSHING-MILL AND ROLLER.
Many years ago, one of my schoolfellows, who had been brought up entirely under the care of some maiden ladies, was visiting a workshop, and must needs put his finger between two revolving rollers. Of course the hand was drawn between them, and simply squeezed flat. The machine was instantly stopped, and the hand extricated; and the strange thing was, that the crushed and shapeless hand afterwards recovered its full power, though not its shape, and was able to touch the keys of the piano.
The whole process of the Rolling-mill is singularly interesting, whether it be used for large or small objects.
Supposing that the grooved rollers of the illustration were cut across so as to present a number of points, it is evident that anything which got between them would be bitten to pieces, each piece being of a tolerably uniform shape.
This plan is now adopted in the granulation of gunpowder. After the future powder has emerged from the hydraulic press in the form called “press-cake,” it was formerly broken to bits with wooden or copper mallets, and then placed in a very peculiar kind of sieve. This was shaped like an ordinary sieve, but the bottom was made of cowhide, pierced with innumerable holes. A round pebble was placed in the sieve, and, when the latter was violently shaken backwards and forwards,the powder was driven through the holes by the pressure of the stone, and was afterwards separated into its various degrees of fineness.
I have only twice seen this process, and confess to have been in a very nervous state on both occasions. The sieve is whirled about with enormous velocity, and the pebble flies round as if it were a thing alive. Let but a broken needle or a fragment of stone get into the sieve, or even let the stone itself break asunder, and there will be an instantaneous explosion, which will hurl the house, the machinery, and the workmen into unknown regions.
Now, however, the mode of granulating powder is radically altered. There is a series of double cylinders, such as shown in the illustration, and each of them has the ridges cut into teeth in regular order. Thus the first set of rollers or cylinders merely bites the press-cake into convenient pieces, though seldom of the same weight.
The press-cake, thus bitten to pieces, is passed through a series of cylindrical sieves, each graduated with the utmost accuracy, and being turned by means of machinery. Being set on a slope, the powder runs by its own weight down them, and all those particles which cannot pass through the meshes are poured out untouched at the lower end.
The portions which are too large to pass the openings of the first sieve are then handed onwards by means of a machine called a “Jacob’s Ladder,” which consists of a series of little vessels or buckets strung on a tape, and revolving over a couple of wheels. The first set of buckets takes the coarsely bitten press-cake to the second set of rollers, the teeth of which are comparatively small. Thence it is passed over to a third set, and so forth, until it is delivered in any quality of grain which may be required.
The modern Mangle, again, affords a good example of this principle. The old obtrusive, costly, and cumbrous Mangle, which was nothing more than a heavy box of stones upon rollers, has given place to the modern system of duplex action in rollers, and one of the old Mangles is not easily to be seen, unless it be worked as a curiosity. In fact, it is nearly as obsolete as the spinning-wheel, which yet may be seen in some of our country villages, where scarcely one per cent, of the population has ever been in a town, and many of them, the womenespecially, make it their boast that they have never been beyond the outskirts of their village.
This clumsy machine is now replaced by the very simple invention which has been in vogue for some years, and which can not only release, but regulate, the pressure at any moment, by means of springs, levers, and weights. This machine is, in fact, exactly the same as that which is represented in the illustration, except that the rollers are quite smooth. They can be adjusted to almost any amount of pressure by levers and weights which are attached to the upper roller, and, when the linen has passed through them, it has undergone the double operation of wringing and mangling. This disposition of the rollers has long been anticipated in the jaws of the Skate which crush to pieces the shells of the whelks, periwinkles, &c., on which the creature feeds.
Beingon the subject of jaws and teeth as a mode of breaking to pieces objects which are placed between them, we will take those implements which grind to powder, or “triturate,” instead of breaking or flattening.
From the very earliest ages, and as soon as man had begun to discover the “staff of life,” the art of grinding naturally assumed an ever-increasing importance.
The first and most primitive mode of grinding corn and converting it into meal was that which was followed by Sarah, when she welcomed her husband’s guests, which we know, from internal evidence, was followed by the uncivilised races who formerly inhabited this island, and by many semi-savages of the present day.
Nothing could be simpler than the machinery used, and nothing could cause a greater waste of muscular power. Two stones were employed, a large one upon which the grain was placed, and a smaller which was held in the hands, and used for grinding the corn to powder, just as the painters of the last century used to grind their colours. The Kafirs of Southern Africa use this simple mill, and so exactly do they keep unconsciously to the customs of long-perished natives, that if one of their mills were buried for a few years and dug up again, it might be mistaken for one of the ancient “querns.”As the stone held in the hand was rounded, it naturally wore a rounded hollow in the lower stone, and this made the process of trituration easier. Perhaps some of my readers may have noticed that when a chemist makes up a prescription, and is obliged to reduce one of the ingredients to powder, he always does so by rubbing, and not by pounding, as is generally believed. He works the pestle round and round the mortar with a kind of twisting motion, and thus obtains a powder much too fine to have been produced by any amount of pounding.
Image unavailable: TOOTH OF ELEPHANT. GRINDSTONE.TOOTH OF ELEPHANT. GRINDSTONE.
The labour of this operation is necessarily very severe, and therefore the Kafir of the present day, as did his predecessors of the long-lost races, declines to do it himself, but hands it over to the women. In Palestine, as in other parts of the world, a simple mill has been invented, which takes away much of the labour, and, above all, releases the grinder from the obligation of leaning with her fall weight upon the upper stone. In this mill the stones are similar. The upper is moved backwards and forwards round a pivot, and the grain is passed between them by means of a conical aperture in the upper stone, which answers the purpose of our “hopper.”
In order to work this mill, two women are required, sitting opposite each other, with the mill between them, holding the same handle, and assisting each other in turning the stone backwards and forwards. No one who has not seen this operation can fully appreciate the force of the saying that “two women shall be grinding at the mill; the one shall be taken, and the other left.”
It is worthy of remark that, even at the present day, the custom of grinding corn is carried out in Palestine as it was so many centuries ago, and that it is repeated in Southern Africa among the Kafir tribes. In both parts of the earth the first sound of early morning is caused by the millstones of the grinding women, and the amount and duration of the noise afford a sure test of prosperity. Cessation of the millstones signifies adversity and a thin population, as has been said by a writer who lived not very far from three thousand years ago. Speaking of tribulation, he mentions that “the grinders cease because they be few, and that the doors shall be shut in the streets when the sound of the grinding is low.”
After awhile improvements were gradually introduced into the business of grinding, not the least of which was covering its surface with ridges, instead of leaving it entirely smooth, as it had been formerly. Millers of the present time know the value of these ridges, and the additional grinding power which this “facing” gives to a stone. One of these stones is represented in the illustration, so as to show the system on which the ridges and grooves are constructed.
Now, passing from Art to Nature, we find that the whole system of the millstone, its movement and its ridged surface, existed in the times when man had not yet come upon earth.
The reader is probably aware that among the tooth-bearing animals there are three types of teeth. First come the incisors, or cutting teeth, which occupy the front of the jaw, and find their fullest development in the rodent animals, such as the beaver, the squirrel, the rabbit, and the rat. Next them come the canine or piercing teeth, which are so highly developed in all the cat tribe. Lastly, there are the molar or masticating teeth, so called from a Latin word signifying a millstone, because their office is to grind food.
As it is with these last that we have now to treat, we will say nothing about the others.
The molar teeth find their greatest development in the Elephant, the structure of whose molars is exactly like that of our modern millstones. There is certainly one very great difference. When the surface of a millstone is rubbed away,the stone must be re-faced, and sooner or later is worn out altogether, and must be replaced with a new one. This, however, is not the case with the Elephant’s molar teeth, which not only keep their facing perfectly sharp, but have the faculty of renewing themselves as fast as they are worn away.
How these important objects are attained we shall now see.
If the reader will refer to the upper left-hand figure of the illustration, he will see that its surface is for the most part round, with irregularly oval figures, close and thick at one end, and almost disappearing at the other. These are the “facings” of the Elephant’s tooth, and they are formed as follows:—
The tooth, which is of enormous size, is not solid, but is composed of a number of plates laid side by side, like a pack of cards when set on their edge. Each of these plates is composed of a hard external layer of enamel, and an internal layer of comparatively soft bony matter. A slice of badly made toast affords a familiar parallel, the half-charred outside representing the enamel, and the soft, sodden interior being analogous to the bony matter. In order to show the arrangement of these plates, a side view of part of the tooth is given on the same illustration. Sometimes, when the teeth of fossil elephants are discovered, these plates all fall asunder, the material which connected them having been dissolved away in the earth.
When, however, we look upon the upper surface of a recent tooth, we see it present the appearance which is shown in the illustration. The elongated oval marks are the edges of the hard enamel plates, while the spaces between them are filled with the soft bony matter. It will be evident, then, that if two teeth such as these be in opposite jaws, and perform the task of grinding food, their surface will always be well “faced.” Owing to the different hardness and density of the enamel and bony substance, the latter will wear away with comparative rapidity, leaving the former to project slightly, and thus to preserve the facing of the natural mill.
This is, indeed, but a modification of the beautiful animal mechanism which keeps the teeth of a rodent animal always sharp, and always bevelled off at the proper angle. If we could invent some plan whereby, in our millstones, we couldmake the facing of much harder material than the stone, we should make an advance in the miller’s art that would render the millstones of the future as far superior to those of the present as are our present millstones to the hand “quern” of the Kafir women.
Yet another improvement has to be made. Would it be possible to construct a millstone which should not only retain its facing, but possess the power of renewing itself in proportion as it is worn out? This property is found in the Elephant’s tooth, and the illustration will give a tolerably good idea of the simple and beautiful mechanism by which it is brought into operation.
The tooth, instead of being one solid mass, consists, as I have already stated, of a series of plates set side by side. These plates are so constructed that they are more worn away in front than behind. In proportion as they are worn, a new tooth is built up behind the old one, and gradually pushes off the old one. Now, if we could only construct millstones with such properties, we should possess an absolutely perfect instrument.
Thereare many useful inventions which depend on the weight of the atmosphere and the creation of a more or less perfect vacuum. There is, for example, the common Pump, which raises water simply by the action of the atmosphere. A pipe passes into the water, and in that pipe an air-tight piston is inserted. When the piston is drawn upwards a vacuum is formed, and the water is at once forced into it by the pressure of the atmosphere.
Then there is the graceful and useful Napier Coffee-making Machine, consisting of a glass globe, and vase of the same material.
Coffee and boiling water are put into the vase, and some hot water into the globe. The two are then connected with the tube, and under the globe is placed a spirit-lamp. Presently the water in the globe boils, expelling the air and filling the globe with steam. The lamp is then removed, and the steam in the globe is condensed, leaving a vacuum. The pressure of the atmosphere then comes to bear upon the coffee in the vase,which is forced through the tube into the globe, producing beautifully clear and well-flavoured coffee.
Surgeryemploys the weight of the atmosphere in the operation called “Cupping,” now rarely employed, but formerly in such constant use that scarcely any man who had attained middle age had not undergone it. The operation was intended for the purpose of removing the blood from some definite spot. Persons, for example, who appeared to have a tendency to apoplexy were regularly cupped between the shoulders twice a year,i.e.in the spring and autumn.
The mode of performing the operation is as follows:—A vase-shaped glass vessel called a cupping-glass is placed close to the skin. The flame of a spirit-lamp is then introduced for a moment in the glass so as to expel the air, and the glass is rapidly placed with its mouth downwards on the skin. If this be done with sufficient rapidity, the partial vacuum in the cupping-glass causes it to adhere to the skin, which is forced into it by atmospheric pressure, as shown in the illustration. The blood is, of course, drawn towards the surface by the same means.
The glass is then quickly removed, and a little brass instrument applied, which, at the touching of a spring, sends out a number of small lancet-blades so formed as to make very slight cuts. The glass is again applied, and rapidly becomes filled with blood from the cuts, the air having forced it in exactly as it forces the coffee in Napier’s machine.
Inthe upper right-hand corner of the illustration is shown the Pneumatic Peg, a comparatively recent invention, and useful in cases where much strength is not required. The base of the peg is fitted with a sort of cup made of india-rubber. When this base is pressed against a smooth and flat surface, such as a pane of glass, the air is forced out of the cup, and a vacuum formed. The pressure of the atmosphere then causes the cup to adhere to the glass with sufficient force to enable objects to be suspended from it.
The boy’s well-known toy, the Sucker, is made on exactly the same principle. A piece of leather, generally circular, though the shape is not of much consequence, has a hole bored throughits centre, so as to allow a string to be attached. The leather is then soaked in water until it is quite soft. If it be firmly pressed on any smooth object, such as a stone, the air is forced from under it, and it becomes capable of sustaining a weight in proportion to its dimensions. As the air has a pressure of about fifteen pounds on every square inch, it is easy to calculate the weight which it will uphold, a margin being left for imperfection of vacuum.