Part 81

We have already stated, that every magnet has two poles; that is, one end is called the north, the other the south pole: the former being considered as capable of attraction; the other, as we shall infer from the subjoined explanations, being far more inert, if at all possessed of an attractive power. When two magnets are brought together with their north poles in contact, they will, instead of cohering, be obviously repelled to a distance corresponding with their respective powers of attraction, when applied individually to unmagnetized needles. The south poles will, in like manner, repel each other; but the north pole of one, and the south pole of the other, will, when approximated, be evidently attracted, and will cohere so as to sustain considerable weights. Iron is the only metal, hitherto known, which is capable of receiving and communicating the magnetic power; but quiet, and the absence of contact, in some respects, are indispensably necessary towards its perfect retention. Thus, when a bar has been impregnated, however abundantly, with the magnetic principle, if it be heated or hammered, the power of attraction will be dissipated; or if a tube filled with iron filings have their surface magnetized, by shaking the tube the magnetic influence will likewise be lost. In some respects the magnetic influence resembles caloric; for it very rapidly communicates to iron, devoid of magnetism, a certain portion of its own powers; which, however, appear to be reproduced instantaneously. As various small fires under one large vessel will thereby heat it, and cause the water it contains to boil, though neither of them individually would produce that effect; so, many weak magnets may, by being united, communicate a power equal to its own, and be made to create an accumulated power, larger than that contained by either of them individually.

There is, however, a seeming contradiction to be found in some authors, who recommend that the weakest magnets should be first applied,--and those more forcible, in succession, according to the power they may possess; the reason assigned being, that the weaker magnets would else, in all probability, draw off some of the accumulated power from the new magnet. But of this there appears no danger, since experience proves that magnets rather gain than lose efficiency by contact, not only with each other, but even with common iron. In fact, the magnetic power may at any time be created by various means: the friction of two pieces of flat and polished bars of iron, will cause them for a short time to attract and to suspend light weights. Soft iron is more easily influenced, but steel will retain the influence longer. Lightning, electricity, and galvanism, being all of the same nature, equally render iron magnetic. It is also peculiar, that when two or more magnets are left for any time with their several north poles in contact, the whole will be thereby weakened; whereas, by leaving a piece of common iron attached to a magnet, the latter will acquire strength. It is also well known that some pieces of steel quickly receive the magnetic influence, while others require considerable labour, and after all are scarcely impregnated. The oxide of iron cannot be impregnated, and those bars that have been so, when they become partially oxydized, lose their power. Hence we see the necessity of preserving the needles of compasses from rust.

Magnets have the power to act notwithstanding the intervention of substances in any degree porous between them and the body to be acted upon: thus, if a needle be put on a sheet of paper, and a magnet be drawn under it, the needle will follow the course of the magnet. The peculiar affinity of the loadstone for iron, is employed with great success, by those who work in precious metals, for the separation of filings, &c. of iron from the smaller particles of gold, &c. A magnet being dipped into the vessel, in which the whole are blended, will attract all ferruginous particles.

To communicate the magnetic power to a needle, let it be placed horizontally; and with a magnet in each hand, let the north pole of one, and the south pole of the other, be brought obliquely in contact over the centre of the needle: draw them asunder, taking care to press firmly, and preserving the same angle or inclination to the very ends of the needles, which should be supported by two magnets, whose ends ought to correspond in polarity with those of the needle. Observe to carry the magnets you press with clear away from the ends of the needle, at least a foot therefrom; repeat the friction in the same manner several times, perhaps six, eight, or ten, and the needle will be permanently magnetized; and, as we have already stated, by using other magnets in succession, the powers of the needle will be proportionably increased.

But no effect will result from the friction if the bars are rusty, or, indeed, not highly polished; their angles must be perfect, and their several sides and ends completely flat. It is, perhaps, one of the most curious of the phenomena attendant on this occult property, that the centre of every magnet is devoid of attraction; yet, that when a needle is placed in a line with a magnet, and within the influence of its pole, that needle almost becomes magnetic, or rather, a conductor, possessing a certain portion of attractive power: and it is no less extraordinary, that the magnet retains its power even in the exhausted receiver of an air-pump; which seems to be a formidable objection to its being influenced by any fluid. Perhaps the opinion entertained by many of our most popular lecturers on this subject, viz. that the earth itself is the great attractor, may be nearest the truth. We are the more inclined towards such an hypothesis, knowing that, at the true magnetic equator, the needle does not dip; and from the well-ascertained fact, that bars of iron, placed for a length of time exactly perpendicular, receive a strong magnetic power, their lower ends repelling the south, but attracting the north poles of magnets applied to them respectively. The direction of the dipping needle was ascertained by one Robert Norman, about two hundred and fifty years ago. He suspended a small magnetic needle, by means of a fine thread round its centre, so as to balance perfectly, over a large magnet: the south pole of the former was instantly attracted by the north pole of the latter. He found, that so long as the needle was held exactly centrical, at about two inches above the magnet, it remained horizontal; but so soon as withdrawn a little more towards one end than the other of the magnet, the equilibrium was destroyed, and that pole of the needle which was nearest to either pole of the magnet was instantly attracted, and pointed downwards thereto. By the magnetic equator, we mean a circle passing round the earth at right angles with the magnetic poles, which do not correspond with the geographical poles, as may be fully understood by the indications of all compasses to points differing from the latter; and as the indications of compasses vary so much both at different times and places, we may reasonably conclude, that the magnetic poles are not fixed. The variation of the dipping-needle has not, in our latitude at least, varied more than half a degree since its depressive tendency was first discovered by Norman.

By means of the mariner's compass,

Tall navies hence their doubtful way explore, And ev'ry product waft from ev'ry shore; Hence meagre want expell'd, and sanguine strife, For the mild charms of cultivated life. _Blacklock._

CHAP. LXXII.

CURIOSITIES RESPECTING THE ARTS, &c.

_Early Invention of several useful Arts--Automaton--Androides-- Extraordinary Pieces of Clockwork--Heidelberg Clock--Strasburg Clock--Clepsydra--Invention of Watches._

What cannot art and industry perform, When science plans the progress of their toil! They smile at penury, disease, and storm; And oceans from their mighty mounds recoil. When tyrants scourge, or demagogues embroil A land, or when the rabble's headlong rage Order transforms to anarchy and spoil; Deep vers'd in man, the philosophic sage Prepares with lenient hand their frenzy t' assuage; 'Tis he alone, whose comprehensive mind, From situation, temper, soil, and clime Explor'd, a nation's various pow'rs can bind, And various orders, in one form sublime Of polity, that 'midst the wrecks of time, Secure shall lift its head on high, nor fear Th' assault of foreign or domestic crime, While public faith, and public LOVE sincere, And industry and law maintain their sway severe. _Beattie._

EARLY INVENTION OF SEVERAL USEFUL ARTS.--Some useful arts must be nearly coeval with the human race; for food, clothing, and habitation, even in their original simplicity, require some display of ingenuity. Many arts are of such antiquity as to place the inventors beyond the reach of tradition; while several have gradually crept into existence without an inventor. The busy mind, however, accustomed to date the progress of science from some particular era, cannot rest till it finds or conjectures a beginning to every art. In all countries where the people are illiterate, the progress of arts is extremely slow. It is vouched by an old French poem, that the virtues of the loadstone were known in France before the year 1180. The mariner's compass was exhibited at Venice, A. D. 1260, by Paulus Venetus, as his own invention. John Goya, of Amalphi, was the first, who, many years afterwards, used it in navigation, and also passed for being the inventor. Though it was used in China for navigation long before it was known to the western nations, yet to this day it is not so perfect as in Europe. Instead of suspending it in order to make it act freely, it is placed upon a bed of sand, by which every motion of the ship disturbs its operation.

Hand-mills, termed _querns_, were early used for the grinding of corn; and when corn came to be raised in greater quantities, horse-mills succeeded. Water-mills for grinding corn are described by Vitruvius. Windmills were known in Greece and Arabia, so early as the seventh century; and yet no mention is made of them in Italy till the fourteenth. That they were not known in England in the reign of Henry VIII. appears from a household book of an earl of Northumberland, contemporary with that king, stating an allowance for three mill horses, "two to draw in the mill, and one to carry stuff to the mill." Water-mills for corn must in England have been of a late date.

The ancients had mirror glasses, and employed glass to imitate crystal vases and goblets; yet they never thought of using it in windows. In the thirteenth century, the Venetians were the only people who had the art of making crystal glass for mirrors. A clock that strikes the hours was unknown in Europe till the end of the twelfth century. And hence the custom of employing men to proclaim the hours during night; which to this day continues in Germany, Flanders, and England. Galileo was the first who conceived an idea that a pendulum might be useful for measuring time; and Huygens was the first who put the idea in execution, by making a pendulum clock. Hook, in 1660, invented a spiral spring for a watch, though a watch was far from being a new invention. Paper was made no earlier than the fourteenth century; and the invention of printing was a century later. Silk manufactures were long established in Greece, before silk-worms were introduced there. The manufacturers were provided with raw silk from Persia; but that commerce being frequently interrupted by war, two monks, in the reign of Justinian, brought eggs of the silk-worm from Hindoostan, and taught their countrymen the method of managing them.

The art of reading made a very slow progress. To encourage that art in England, the capital punishment for murder was remitted, if the criminal could but read, which in law language is termed _benefit of clergy_. One would imagine that the art must have made a very rapid progress when so greatly favoured: but there is a signal proof of the contrary, for so small an edition of the Bible as six hundred copies, translated into English in the reign of Henry VIII. was not wholly sold off in three years. The people of England must have been profoundly ignorant in Queen Elizabeth's time, when a forged clause, added to the twentieth article of the English creed, passed unnoticed till about sixty years ago.

The discoveries of the Portuguese on the west coast of Africa, afford a remarkable instance of the slow progress of the arts. In the beginning of the fifteenth century, they were totally ignorant of that coast beyond Cape Non, in 28 degrees, north latitude. In 1410, the celebrated Prince Henry of Portugal fitted out a fleet for discoveries, which proceeded along the coast to Cape Bajadore, in 26 degrees, but had not courage to double it: and seventy-six years elapsed before this was done by Bartholomew Diaz, in 1486!

Description of AN AUTOMATON.--This is a machine, so constructed by means of weights, levers, springs, wheels, &c. as to move for a considerable time, as if it were endued with animal life. According to this definition, clocks, watches, and all machines of that kind, may be ranked as a species of automata. But the word is most commonly applied to such machines as are made in the form of men and other animals, at the same time that their internal machinery is so contrived, that they seem voluntarily to act like the animals they represent. Archytas of Tarentum, who lived A. C. 400, is said to have made a wooden pigeon that could fly. It is also recorded, that Archimedes made similar automata; that Regiomontanus made a wooden eagle, which flew forth from the city of Nuremburg, met the emperor, saluted him, and returned; also that he made an iron fly, which flew out of his hand at a feast, and returned again after flying about the room. Dr. Hook made the model of a flying chariot, capable of supporting itself in the air. Many other surprising automata have been exhibited in the present age. M. Vaucanson made a duck, which could eat, drink, and imitate exactly the voice of a natural one; and what is still more surprising, the food it swallowed was evacuated in a digested state, or at least considerably altered, on the principles of solution. The wings, viscera, and bones, were so formed, as greatly to resemble those of a living duck; and the actions of eating and drinking shewed the strongest resemblance, even to muddling the water with its bill.

M. de Droz, of la Chaux de Fonds, in the province of Neuchatel, has also executed some curious pieces of mechanism. One was a clock, presented to the king of Spain, which had, among other curiosities, a sheep that imitated the bleating of a natural one, and a dog that watched a basket of fruit, and which barked and snarled if any one attempted to take it away; if it was actually taken, it would bark till it was restored. A son of this gentleman has also made some extraordinary pieces, particularly an oval gold snuff-box, about four inches long, three broad, and one and a half thick. It is double, having an horizontal partition, with a lid to each of its parts. One contains snuff; but in the other, as soon as the lid is opened, there rises up a very small bird, (for it is only three-quarters of an inch from the beak to the extremity of the tail,) of green-enamelled gold, sitting on a gold stand, which immediately wagging its tail and shaking its wings, and opening its bill of white-enamelled gold, pours forth a clear melodious song, capable of filling a room of twenty or thirty feet square with its melody. The same gentleman exhibited an automaton in England, of the figure of a man, as large as life. It held in its hand a metal style, under which was a card of Dutch vellum. A spring was then touched, and the internal machinery being thus set a-going, the figure began to draw elegant portraits, and likenesses of the king and queen facing each other; and it was curious to observe, with what precision the figure lifted up its pencil, in the transition of it from one point of the picture to another, without making the least blunder whatever; for instance, in passing from the forehead to the eye, nose, and chin, or from the waving curls of the hair to the ear, &c. The first card being finished, the figure rested, until a second was completed, and so on through five separate cards put to it, on all of which it delineated different subjects, but five or six was the extent of its surprising powers.

ANDROIDES.--This is an automaton, in the figure of a man, which, by virtue of certain springs, &c. duly contrived, walks, and performs other external functions of a man. Albertus Magnus is recorded as having made a famous androides, which is said not only to have moved, but to have spoken. Thomas Aquinas is said to have been so frightened when he saw this head, that he broke it to pieces; upon which Albert exclaimed, "_Periit opus triginta annorum!_"

Artificial puppets, which, by internal springs, run upon a table, and, as they advance, move their heads, eyes, or hands, were common among the Greeks, and from thence they were brought to the Romans. Figures, or puppets, which appear to move of themselves, were formerly employed to work miracles; but this use is now superseded, and they serve only to display ingenuity, and to answer the purposes of amusement. One of the most celebrated figures of this kind, was constructed and exhibited at Paris, in 1738; and a particular account of it was published in the memoirs of the academy for that year. This figure represents a flute-player, which was capable of performing various pieces of music, by wind issuing from its mouth into a German flute, the holes of which it opened and shut with its fingers: it was about five and a half feet high, placed upon a square pedestal four and a half feet high, and three and a half broad. The air entered the body by three separate pipes, into which it was conveyed by nine pairs of bellows, that expanded and contracted, in regular succession, by means of an axis of steel turned by clock-work. These bellows performed their functions without any noise, which might have discovered the manner by which the air was conveyed to the machine.

The three tubes, which received the air from the bellows, passed into three small reservoirs in the trunk of the figure. Here they united, and, ascending towards the throat, formed the cavity of the mouth, which terminated in two small lips, adapted in some measure to perform their proper functions. Within this cavity was a small moveable tongue, which by its motion, at proper intervals, admitted the air, or intercepted it in its passage to the flute. The fingers, lips, and tongue, derived their proper movements from a steel cylinder, turned by clock-work. This was divided into fifteen equal parts, which, by means of pegs, pressing upon the ends of fifteen different levers, caused the other extremities to ascend. Seven of these levers directed the fingers, having wires and chains fixed to their ascending extremities, which, being attached to the fingers, made them to ascend in proportion as the other extremity was pressed down by the motion of the cylinder, and _vice versâ_; then the ascent or descent of one end of a lever produced a similar ascent or descent in the corresponding fingers, by which one of the holes of the flute was occasionally opened or stopped, as it might have been by a living performer. Three of the levers served to regulate the ingress of the air, being so contrived as to open and shut, by means of valves, the three reservoirs above-mentioned, so that more or less strength might be given, and a higher or lower note produced, as occasion required. The lips were, by a similar mechanism, directed by four levers, one of which opened them, to give the air a freer passage, the other contracted them, the third drew them backward, and the fourth pushed them forward. The lips were projected upon that part of the flute which receives the air, and, by the different motions already mentioned, modified the tune in a proper manner. The remaining lever was employed in the direction of the tongue, which it easily moves so as to shut or open the mouth of the flute. The just succession of the several motions, performed by the various parts of this machine, was regulated by the following simple contrivance.

The extremity of the axis of the cylinder terminated on the right side by an endless screw, consisting of twelve threads, each placed at the distance of a line and a half from the other. Above this screw was fixed a piece of copper, and in it a steel pivot, which, falling in between the threads of the screw, obliged the cylinder to follow the threads; and, instead of turning directly round, it was continually pushed to one side. Hence, if a lever was moved, by a peg placed on cylinder, in any one revolution, it could not be moved by the same peg in the succeeding revolution, because the peg would be moved a line and a half beyond it by the lateral motion of the cylinder.

Thus, by an artificial disposition of these pegs in different parts of the cylinder, the statue was made, by the successive elevation of the proper levers, to exhibit all the different motions of a flute-player, to the admiration of every one who saw it. Another figure, constructed by the same artist, Vaucanson, played on the shepherd's pipe, held in its left hand, and with the right beat upon a drum.