MAGNETISM is supposed to have been first rendered useful about the end of the twelfth, or at least very early in the thirteenth, century, by John de Gioja, a handicraft of Naples, who noticed the peculiar attraction of metals, and iron in particular, towards certain ma.s.ses of rude ore; the touch of which communicated to other substances of a ferruginous nature, especially iron or steel bars, the property of attraction: these touched bars he observed to have a peculiar and similar tendency towards one particular point; that when suspended in equilibrio, by means of threads around their centres, they invariably turned towards the same point; and that, when placed in a row, however adversely directed, they soon disposed themselves in perfectly parallel order. In this instance he improved upon the property long known to, but not comprehended or applied to use by, the ancients, who considered the loadstone simply as a rude species of iron ore, and curious only so far as it might serve to amuse.

Gioja being possessed of a quick understanding, and of a strong mind, was not long in further ascertaining the more sensible purposes to which the magnet might be appropriated. He accordingly fixed various magnets upon pivots, supporting their centres in such a manner as allowed the bars to traverse freely. Finding that, however situated within the reach of observation and comparison, they all had the same tendency, he naturally concluded them to be governed by some attraction, which might be ultimately ascertained and acted upon. He therefore removed into various parts of Italy, to satisfy himself whether or not the extraordinary impulse which agitated these bars, that had been magnetized by friction, existed only in the vicinity of Naples, or was general. The result of his researches appears to be, that the influence was general, but that the magnets were rendered extremely variable, and fluctuated much, when near large ma.s.ses of iron. The experiments of Gioja gave birth to many others, and at length to a trial of the magnetic influence on the surface of the water. To establish this, a vessel was moored out at sea, in a direction corresponding with that of the magnet; and a boat, having a magnet equipoised on a pivot at its centre, was sent out at night in the exact line indicated thereby; which, being duly followed, carried them close to the vessel that was at anchor. Thus the active power of attraction appeared to be established on both elements, and in the course of time the magnet was fixed to a card, marked with thirty-two points, whereby the mariner's compa.s.s was presented to us. The points to which the magnet always turned itself, being generally in correspondence with the meridian of the place where it acted, occasioned the extremities of the bars to be called poles. Succeeding experiments proved, that the magnetic bar never retained an exactly horizontal position; but that one of its poles invariably formed an angle with any perfect level, over which it was placed: this was not so very measurable in a short bar, but in one of a yard in length was formed to give several degrees of inclination. This, which is called "the dip of the needle," (or magnet,) seems to indicate that the attracting power is placed within the earth. What that attracting power is, we cannot determine; some consider it to be a fluid, while others conjecture it to be an immense ma.s.s of loadstone, situated somewhere about the north pole. The difficulty is, however, considerably increased by the known fact of the needles of compa.s.ses not always pointing due north; but in many places varying greatly from the meridional lines respectively; and from each other at different times and places.

The facility with which a meridional line may be drawn by solar observation, and especially by taking an azimuth, fortunately enables navigators to establish the variation between the true northern direction, and that indicated by the magnet attached to the card of the compa.s.s.

Nevertheless, we have great reason to believe, that, for want either of accurate knowledge of the prevalent variations, or from inattention thereto, many vessels, of which no tidings were ever heard, have been cast away; it being obvious, that a false indication of the northern point, in many places amounting to nearly the extent of twenty-five degrees, must produce so important an error in a vessel's course, as to subject her to destruction on those very shoals, rocks, &c. of which the navigator unhappily thinks he steers perfectly clear. To obviate such danger, as far as possible, all modern sea-charts have the variations of the compa.s.s in their several parts duly noted down; and in reckoning upon the course steered by the compa.s.s, an allowance is usually made for the difference between the apparent course by the compa.s.s, and the real course, as ascertained by celestial observation. Under circ.u.mstances so completely contradictory, the principle of magnetism must remain unknown: we know not of any hypothesis which strikes conviction on our minds, or which seems to convey any adequate idea of the origin, or _modus operandi_, of this wondrous influence. All we can treat of is, the effect; also of the appearances which guide our practice, and of the manner in which the attractive power may be generated and increased. In regard to the latter point, namely, the generation and increase of the magnetic attraction, we shall endeavour to give a brief but distinct view of what relates thereto: observing, that where volcanic eruptions are frequent, and in those lat.i.tudes where the Aurora Borealis is distinctly seen, the needle or magnet is sensibly affected.

Previously to earthquakes, as well as during their action, and while the northern lights are in full display, no reliance can be placed on the compa.s.s; the card of which will appear much agitated. This has given rise to the opinion held by some, that the power is a fluid: to this, however, there appear so many objections, that we are more disposed to reject than to favour it, although under the necessity of confessing, that we are not able to offer one that may account satisfactorily for the various phenomena attendant upon magnetism.

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 acc.u.mulated 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 a.s.signed being, that the weaker magnets would else, in all probability, draw off some of the acc.u.mulated 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 compa.s.ses 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 pa.s.sing 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 compa.s.ses to points differing from the latter; and as the indications of compa.s.ses 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 lat.i.tude at least, varied more than half a degree since its depressive tendency was first discovered by Norman.

By means of the mariner's compa.s.s,

Tall navies hence their doubtful way explore, And ev'ry product waft from ev'ry sh.o.r.e; 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' a.s.suage; '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' a.s.sault 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 compa.s.s 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 pa.s.sed 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 quant.i.ties, 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 gla.s.ses, and employed gla.s.s 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 gla.s.s 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, pa.s.sed 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 lat.i.tude. 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 Regiomonta.n.u.s 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 part.i.tion, 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 pa.s.sing 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 amus.e.m.e.nt. 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, pa.s.sed 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 pa.s.sage 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 versa_; 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 pa.s.sage, 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.

The performances of Vaucanson were imitated, and even exceeded, by M. de Kempelin, of Presburg, in Hungary. The androides constructed by this gentleman in 1769, was capable of playing at chess. It was first brought over to England in 1783, and has often been exhibited since that period.

It is thus described: The figure is as large as life, in a Turkish dress, seated behind a table, with doors three and a half feet long, two deep, and two and a half high. The chair on which it sits is fixed to the table, which is made to run on four wheels. It leans its right arm on the table, and in its left hand holds a pipe; with this hand it plays after the pipe is removed. A chess-board of eighteen inches is fixed before it. The table, or rather chest, contains wheels, levers, cylinders, and other pieces of mechanism, all of which are publicly displayed. The vestments of the figure were then lifted over its head, and the body was seen full of similar wheels. There is a little door in its thigh, which is likewise opened: and with this, and the table also open, and the figure uncovered, the whole is wheeled about the room. The doors are then shut, and the automaton is ready to play; but it always takes the first move. At every motion the wheels are heard; the image moves its head, and looks over every part of the chess-board. When it checks the queen, it shakes its head twice; and thrice in giving check to the king. It likewise shakes its head when a false move is made, replaces the piece, and makes its own move, by which means the adversary loses one. M. de Kempelin exhibited his automaton at Petersburg, Vienna, Paris, and London, before thousands, many of whom were mathematicians, and chess players, and yet the secret by which he governed the motion of its arm was never discovered. He valued himself upon the construction of a mechanism, by which the arm could perform ten or twelve moves. It then needed to be wound up like a watch, after which it was capable of continuing the same number of motions. This automaton could not play unless M. de Kempelin, or his a.s.sistant, was near it to direct its movements. A small square box was frequently consulted by the exhibiter during the game, and in this consisted the secret, which the inventor declared he could communicate in a moment. Any person who could beat M. de Kempelin at chess, was sure of conquering the automaton.

EXTRAORDINARY PIECES OF CLOCK-WORK.--Amongst the modern clocks, those at Strasburg and Lyons are very eminent for the richness and variety of their furniture, and for their motions and figures. In the former, a c.o.c.k claps his wings, and proclaims the hour, and an angel opens a door, and salutes the Virgin; while the Holy Spirit descends on her, &c. In the latter, two hors.e.m.e.n encounter, and beat the hour on each other; a door opens, and there appears on the theatre the Virgin, with Jesus Christ in her arms; the Magi, with their retinue, marching in order, and presenting their gifts; two trumpeters sounding all the while to proclaim the procession.

These, however, are excelled by two which were lately made by English artists, and sent as a present from the East India Company to the Emperor of China. These clocks are in the form of chariots, in which are placed, in a fine att.i.tude, a lady, leaning her right hand upon a part of the chariot, under which is a clock of curious workmanship, little larger than a shilling, that strikes and repeats, and goes eight days. Upon her finger sits a bird finely modelled, and set with diamonds and rubies, with its wings expanded in a flying posture, and it actually flutters for a considerable time on touching a diamond b.u.t.ton below it; the body of the bird (which contains part of the wheels that in a manner give life to it) is not the bigness of the 16th part of an inch. The lady holds in her left hand a gold tube not much thicker than a large pin, on the top of which is a small round box, to which a circular ornament, set with diamonds not larger than a sixpence, is fixed, which goes round nearly three hours in a constant regular motion. Over the lady's head, supported by a small fluted pillar not bigger than a quill, are two umbrellas, under the largest of which a bell is fixed, at a considerable distance from the clock, and seems to have no connection with it; but from which a communication is secretly conveyed to a hammer that regularly strikes the hour, and repeats the same to the clock below. At the feet of the lady is a golden dog; before which, from the point of the chariot, are two birds fixed on spiral springs, the wings and feathers of which are set with stones of various colours, and appear as if flying away with the chariot, which, from another secret motion, is continued to run in a straight, circular, or any other direction; while a boy that lays hold of the chariot behind, seems also to push it forward. Above the umbrella are flowers and ornaments of precious stones; and it terminates with a flying dragon set in the same manner. The whole is of gold, most curiously executed, and embellished with rubies and pearls.

HEIDELBERG CLOCK.--At Heidelberg, in Germany, upon the town-house, was a clock with divers motions; and when the clock struck, the figure of an old man pulled off his hat, a c.o.c.k crowed, and clapped his wings, soldiers fought with one another, &c.: but this curious piece of workmanship, with the castle and town, were burnt by the French, who committed at the same time the most inhuman barbarities upon the people, when they took those garrisons, in the year 1693.

STRASBURG CLOCK.--At Strasburg, there is a clock, of all others the most famous, invented by Conradus Dasipodius, in the year 1573. Before the clock stands a globe on the ground, shewing the motions of the heavenly bodies. The heavens are carried about by the first mover, in twenty-four hours; Saturn, by his proper motion, is carried about in thirty years; Jupiter in twelve, Mars in two, the Sun, Mercury, and Venus, in one year; and the Moon in one month. In the clock itself there are two tables on the right and left hand, shewing the eclipses of the Sun and Moon from the year 1573, to the year 1624. The third table in the middle is divided into three parts. In the first part, the statue of Apollo and Diana shews the course of the year, and the day thereof, being carried about in one year; the second part shews the year of our Lord, and the equinoctial days, the hours of each day, the minutes of each hour, Easter-day, and all other feasts, and the Dominical Letter. The third part has the geographical description of all Germany, and particularly of Strasburg, with the names of the inventor, and of all the workmen. In the middle frame of the clock is an astrolabe, shewing the sign in which each planet is every day, and there are the statues of the seven planets, upon a round piece of iron, lying flat; so that every day the statue of the planet that rules the day comes forth, the rest being hid within the frames, till they come out by course at their day, as the sun upon Sunday, and so for all the week. And there is also a terrestrial globe, which shews the quarter, the half hour, and the minutes. There is also the skull of a dead man, and statues of two boys, one of whom turns the hour-gla.s.s when the clock has struck, the other puts forth the rod in his hand at each stroke of the clock.

Moreover, there are the statues of the Spring, Summer, Autumn, and Winter, and many observations of the moon.

In the upper part of the clock are four old men's statues, which strike the quarters of the hour; the statue of Death comes out at each quarter to strike, but is driven back by the statue of Christ, with a spear in his hand, for three-quarters; but in the fourth quarter, that of Christ goes back, and that of Death strikes the hour, with a bone in his hand, and then the chimes sound. On the top of the clock is an image of a c.o.c.k, which twice in the day cries aloud, and claps his wings. Besides, this clock is decked with many rare pictures: and being on the inside of the church, carries another frame to the outside of the wall, wherein the hours of the sun, the courses of the moon, the length of the day, and such other things, are set out with great art.

CLEPSYDRA--is a water-clock, or instrument to measure time by the fall of a certain quant.i.ty of water, and is constructed on the following principles.--Suppose a cylindrical vessel, whose charge of water flows out in twelve hours, were required to be divided into parts, to be discharged each hour. 1. As the part of time is to the whole time, Twelve, so is the same time Twelve to a fourth proportional Hundred-and-forty-four. Divide the alt.i.tude of the vessel into one hundred and forty-four equal parts: here the last will fall to the last hour; the three next above, to the last part but one; the five next, to the tenth hour; lastly, the twenty-three last to the first hour. For since the times increase in the series of the natural numbers 1, 2, 3, 4, 5, &c. and the alt.i.tudes, if the numeration be in a retrograde order from the twelfth hour, increase in the series of the unequal numbers 1, 3, 5, 7, 9, &c. the alt.i.tudes computed from the twelfth hour will be as the squares of the times 1, 4, 9, 16, 25, &c. Therefore the squares of the whole time, one hundred and forty-four, comprehend all the parts of the alt.i.tude of the vessel to be emptied. But a third proportional to 1 and 12, is the square of twelve, and consequently it is the number of equal parts in which the alt.i.tude is to be distributed, according to the series of the unequal numbers, through the equal interval of hours.

There were many kinds of clepsydrae among the ancients; but they all had this in common, that the water ran generally through a narrow pa.s.sage, from one vessel to another, and in the lower was a piece of cork, or light wood, which, as the vessel filled, rose up by degrees, and shewed the hour.

We shall in the next place make a few remarks on the INVENTION OF WATCHES.--The invention of spring or pocket watches belongs to the 17th century. It is true, we find mention made of a watch presented to Charles V. in the history of that prince: but this, in all probability, was no more than a kind of clock to be set on a table, some resemblance whereof we have still remaining in the ancient pieces made before the year 1670.

There was also a story of a watch having been discovered in Scotland, belonging to King Robert Bruce; but this we believe has turned out altogether erroneous. The glory of this very useful invention lies between Dr. Hooke and M. Huygens; but to which of them it properly belongs, has been greatly disputed; the English ascribing it to the former, and the French, Dutch, &c. to the latter. Mr. Derham, in his Artificial Clockmaker, says, roundly, that Dr. Hooke was the inventor; and adds, that he contrived various ways of regulation. One way was, with a loadstone; another with a tender straight spring, one end whereof played backwards and forwards with the balance, so that the balance was to the spring as the bob to a pendulum, and the spring as the rod thereof. A third method was, with two balances, of which there were divers sorts; some having a spiral spring to the balance for a regulator, and others not. But the way that prevailed, and which still continues to prevail, was, with one balance, and one spring running round the upper part of the verge; though this has a disadvantage, from which those with two springs, &c. were free, since a sudden jerk, or confused shake, will alter its vibrations, and disturb its motion.