plates in one unvarying order, the zinc and copper | two simple gases of which it is composed are obtained. succeeding each other alternately throughout the series. When several troughs are connected together, as in figure 6, the apparatus is called a battery. The cells

Fig. 6.

are usually charged with acids diluted with water to a certain extent; muriatic acid being diluted with five parts, and sulphuric acid with fifty parts of water. By experiments, it has been ascertained that increase of galvanic power is not in the ratio of an increased size of plates, but in the ratio of an increased number. Several troughs of small plates will thus have greater power than one trough with a greater superficies of metal. It may be further mentioned, that if a battery is to consist of a certain number of square feet of plates, then, for producing calorific effects, or the ignition of metallic leaves and other combustibles, the plates ought to be large; for chemical effects, the size ought to be small, and the plates numerous; and for physiological effects, that is, for operating on the animal system, they ought to be made of an intermediate size.

The chemical changes effected by the electricity of galvanic action, are among the most remarkable phenomena in physical science. We shall instance a few of these facts, gathered from the best authorities. If a plate of zine, and another of copper, be immersed in very dilute sulphuric acid, without touching or communicating with each other, the zinc will be acted upon by the acid; part of the water will be decomposed, its oxygen combining with the zinc, and forming oxide of zinc, and its hydrogen will be disengaged in the form of gas from the surface of the zinc plate. The copper is not acted upon. If the metals be brought into contact, the oxidation goes on with greater rapidity and energy, although without the evolution of the same quantity of hydrogen gas from the oxidating surface. But, from the whole fluid, hydrogen is disengaged in quantity exactly corresponding to that of the oxygen derived from the water, and the greater portion of it rises in a copious stream of bubbles from the surface of the copper plate, which remains unacted upon as before.

If, however, an acid, such as nitric acid, capable of acting upon the copper as well as upon the zinc, be employed instead of the sulphuric acid, similar phenomena will take place, with this additional circumstance, that the action of the acid upon the copper will cease the instant the galvanic circuit is completed; and instead of nitrous gas being formed on the surface of the copper, which happens before the circuit is formed, only bubbles of pure hydrogen will make their appearance; and the copper is protected from all further action, the zine being, as in the former case, oxidated and dissolved with additional energy. It is on this principle that Sir Humphry Davy effected the protection of the copper sheathing of ships from the corrosion of sea-water, by placing in contact with it pieces of zinc or iron, on which sea-water exerts a greater chemical action than on copper. Among the simplest effects of galvanism upon fluid conductors, is the resolution of water into its two gaseous elements, oxygen and hydrogen. If the water employed be not perfectly pure, other substances besides the two components of water make their appearance at the two wires employed in the experiment. The apparent formation of these substances greatly puzzled the early experimentalists; but Sir Humphry Davy proved that, when the water is perfectly free from any foreign ingredient, only the

He also discovered, that, under the influence of voltaic electricity, neutral salts existing in any solution were decomposed, the acid portion being accumulated around the positive wire on the same points where oxygen was disengaged; while the bases, whether earthy, alkaline, or metallic, were at the same moment transferred, along with the hydrogen, to the negative wire.

Phenomena of a still more extraordinary nature presented themselves to Sir Humphry Davy in the further prosecution of these inquiries. It was discovered that the elements of compound bodies were actually con veyed, by the influence of the electric current, through solutions of substances, on which, under other circum stances, they would have exerted an immediate and powerful chemical action, without any such effect being produced. Acids, for example, may be transmitted from one cup, connected with the negative pole, to another on the opposite or positive side, through a portion of fluid in an intermediate cup, tinged with any of the vegetable-coloured infusions, which are instantly red dened by the presence of an acid, without occasioning the slightest change of colour. The same happens also with alkalies. If three cups be arranged, and connected with each other in a series by moistened cotton, the middle cup, and also the one next to the positive side of the battery, being filled with blue infusion of cabbage or of litmus, and the cup next to the negative side containing a solution of sulphate of soda, on the series being placed in the voltaic circuit, a red tinge will soon be perceived in the water of the positive cup, which will become strongly acid. It is evident that the sul phuric acid so transferred must have passed through the fluid in the middle vessel, but without affecting the coloured solution in its passage. By reversing the connexions with the poles of the battery, a similar transfer of the alkali will be made: it will be collected in the tinged water of the negative cup, which it will render green; but the intermediate portion of fluid will not, either in this or in the former case, exhibit any trace of the substance which is carried through it by the influence of electricity. Cohesion, however, where powerful, as might have been expected, intercepts the transmission of the substance. So powerful is this myste rious agent, that the minutest portions of a substance, acted upon by either of the wires, is collected around it.

"An interesting class of experiments are due to Mr Crosse, on the employment of electricity, in a state of high tension, to form mineral and other substances. There is a cavern near Broomfield, of which the vault is covered with arragonite, and carbonate of lime, and fine crystals. The water which drips from this vault holds in solution ten grains of carbonate of lime, and a little sulphate of the same to each pint. A glass filled with this water was submitted to the action of a battery consisting of 200 pairs of plates, and at the expiration of ten days the negative pole was found to have formed rhomboidal crystals of carbonate of lime, accompanied by some gas-bubbles, and in less than a month after, the wire was covered with regular and irregular crystals; whence it follows that the bicarbonate was decomposed into carbonate and carbonic acid gas. He also let the water drop on a piece of brick subjected to a current from 100 five-inch plates, the brick being supported by a funnel which conducted the water into a vessel below; after four or five months the brick near the negative pole of the battery was covered with carbonate of lime, while near the positive pole were disposed prismatic crystals of arragonite; and the same experiment being repeated with fluosilicic acid, regular hexahedral pyramids, similar in all respects to quartz. were obtained; those which were left in a dry place acquired sufficient hardness to scratch glass; the others had not that power, and gradually lost their transparency. In his varied experiments of this nature, he has succeeded in forming, by means of the galvanic battery, the following minerals :-carbonate of lime, arragonite, quartz, protoxide of copper, arseniate of copper, and its blue and green carbonates, phosphate

of copper, carbonate of lead, chalcedony, &c."-Penny | retain their contractility. The convulsions are so geneCyclopedia.

ral, as often to impress the spectator with a belief that the animal has been restored to the power of sensation, and that it is suffering the most cruel torture. The eyes open and shut in their sockets spontaneously, as if re-endued with vision; the nostrils vibrate, as in the act of smelling; and the movements of mastication are imitated by the jaws. The experiments which are calculated to produce the greatest terror and astonishment are those made upon the bodies of recently executed criminals; but for any account of these operations we cannot afford room in our limited pages.

Why compounds, when placed in a galvanic circuit, tre decomposed, and why their elements collect, some around the positive and others around the negative pole of the battery, are questions which have never been satisfactorily solved. Sir Humphry Davy suggested the theory that all bodies possess natural elecirical energies, which are inherent in them, whether they are in a state of combination or not. Oxygen, clorine, iodine, and acids, according to the theory, are naturally negative; while inflammables, as hydroges, sulphur, &c., and metals, are naturally positive. Hence, when the combinations of these substances are subverted by the galvanic influence, the substances are evolved in the electric state natural to them; and as it is a law of electricity that bodies in oppote states attract each other, the oxygen, being neive, is immediately attracted by the positive wire, while the inflammable or metallic base, being naturally psitive, is attracted by the negative wire. In this way, the uniform appearances of these bodies at their particular poles are accounted for. Thus, if hydrogen is naturally positive, and oxygen naturally negative, acarding to the laws of electricity, they must attract each other; and if these opposite states are sufficiently evated to give them an attractive force superior to the power of aggregation, they may be expected to combine; and, in like manner, other bodies, whose particles are in different states, may from this cause be united together. If a body, also, whose electrical Galvanism has latterly been applied to the protection energy exceeds that of one of the substances combined, of plants from worms and slugs, as appears from the be brought to act upon these, it may expel that ingre- following notice in a Liverpool newspaper :-" The prodient, and take its place; and this may be the cause of tector consists of a conical ring of zinc about four inches what is called decomposition from elective affinity. in height, the top end flanked off about a quarter of an The agency of the galvanic apparatus, then, in pro-inch, and cut into numerous vandyked points; and imducing decomposition, it is conceived, is this that the mediately under is a ring of copper neatly fitted. The two wires placed in contact with the compound are in bottom of the zine ring is pressed into the soil until the sates of electricity more intensely elevated than the lower edge of the copper ring is an inch and a half ratural states of the two ingredients; hence the attrac- above the surface, care being taken to enclose within of these two highly electrified points overcomes the ring the stems of such plants as require them, that subsisting between these ingredients: they are otherwise the mullusca will find a road to them by the separated, and immediately drawn to the respective stems. The mollusca may crawl up the zinc with impoles the positive constituent to the negative wire, punity, but on coming in contact with the copper, will and the ingredient which is naturally negative to the receive a galvanic shock and fall to the ground. The positive wire. apparatus acts in wet or dry weather, and is always in operation. Its appearance is like a flower-pot, and it is cheap and durable. After a trial of twelve months by Mr Cuthbert, the inventor, he found that not a plant to which it was applied was injured.”

The effects of galvanism upon the functions of secretion are the most remarkable as well as the most inexplicable. That it acts especially, and in a peculiar manner, upon the gastric juice, a fluid essentially subservient to the process of digestion, there can be no doubt. Perhaps the various functional parts of the body form a sort of galvanic battery, by which a regular circulation of this subtile and mysterious fluid is kept up. On the supposition that such is the case, galvanism has been applied with good effect in medicine, in the cure of nervous disorders. Tic doloureux, which is a chronic derangement in the nervous energy, has been subjected to the influence of galvanic currents, and these, in particular cases, have completely removed the complaint. It is perhaps necessary, by way of precaution, to say that all such applications ought only to be made under the special direction of a skilled medical practitioner.

With respect to the physiological effects of galvanic action, it may be observed that the shock received by the human body from the voltaic pile is similar to that resulting from a large electrical battery very weakly charged. Twenty pair of plates are generally sufficient to give a shock which is sometimes felt in the arms. With a hundred pair, it extends to the shoulders. A continued flow of the current through the body is accompanied by a continued aching pain. The impression made upon some of the nerves of the face when they form part of the circuit, is accompanied by the sensation of a vivid flash of light. When a piece of zinc and a piece of copper are placed, the one above and the ather below the tongue, which must be in a moist state, peculiar taste is experienced. This is supposed to arise from the saliva of the mouth having been decomposed by the galvanic action, and not merely the effect of a direct impression of the electric current on the Derves of the tongue. When the current of voltaic electricity is made to pass along a nerve distributed to any of the muscles of voluntary motion, they are thrown into violent convulsive contractions. The susceptibility of some animals is very great, and numerous curious experiments may be performed with them. If an earthWorm be placed upon a crown piece which lies upon a plate of zinc of larger size, it will suffer no inconvenieace as long as it remains in contact with the silver only; but the moment it has stretched out its head, and touched the zinc, so as to complete the galvanic tirele, it suddenly recoils, as if it had felt a severe shock. If the battery be powerful, small animals may be easily killed. Striking effects are produced by galvanism in the muscles of an animal after death, as long as they

Electrotyping. In 1839, the galvanic principle, in relation to the deposition of metal from a metallic solution, was applied by Mr Thomas Spencer of Liverpool to the multiplying of plates of engraved copper, medals, &c. The nature of this most ingenious discovery, which was first brought into public notice at a meeting of the Liverpool Polytechnic Society (Sept. 12, 1839), will be best understood by describing the process which is now ordinarily pursued.

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We take a trough or box, which may be represented by fig. 7. This box is divided lengthwise by a thin partition P, composed of sycamore, that being a porous and durable material. C is a copper plate suspended in one of the cells by a wire attached to an upper rod of metal R, traversing the mouth part of the box. In the other cell is similarly placed a plate of zinc, nearly the size of the copper. The zine is similarly suspended by a wire from the traversing rod above. A wire passing over direct from the copper to the zinc, would answer the same purpose of communication, but the plan of an intervening rod with

Fig. 7.

Plaster casts (Mr Barclay proceeds to mention) are, next to seal impressions, most easy of attainment. To electrotype from these, it is necessary to soak them in melted white wax, stearine, or tallow, which is thus Various other objects may be multiplied by this kind best effected :-Take a shallow vessel, in which put a of electrotyping, as it has been named; for example, little wax, and hold it over the flame of a lamp; when dies for seals, medals, plaster-casts, &c. Mr Barclay, melted, drop in the plaster cast, face upwards, taking a seal-engraver in Gerrard Street, Soho, London, has care the wax does not overflow the surface; in a short carried the practice of electrotyping metal seal stamps time, by keeping it warm, the wax will ascend in the to great perfection. A small tract which he has pub-plaster, and when it is observed to have equally perJished on the subject, furnishes the following observa-vaded the surface, it must be removed and placed on a tions on the method to be pursued. It will be noticed piece of blotting-paper, to absorb the superfluous wax, that he multiplies the dies or seals from impressions which it will better effect by being kept warn for a taken in sealing-wax :-" The paper on which the im-short period. It must then be laid by for twelve hours pressions are to be taken should be thick and soft, like at least, after which time it may be well brushed with that on which music is printed, dried over the light, a soft brush and black-lead, without fear of injury. To and spread flat-the wax should not be put into the attach the copper wire, use melted bees-wax at the light, or allowed to flame; when on the paper, it must back of the cast, having a bent portion of the wire near be kept fluid, while by stirring to the required size and the surface, with which to make the connexion with the gradually diminishing the heat, all bubbles are re-black-leaded surface, or the wire may be made to surmoved: when nearly cool, make the seal of the same round the cast. As in the case of the wax impression, temperature as the wax, or sufficiently warm as to be varnish the wire and the parts of the cast on which no fe on the back of the hand. If the scal be too | deposit is required. Having equally oiled the subject,

a plaster cast may be made as follows:-Take fresh | markably ingenious devices, it was long in being heard of paster, and having a little water in a basin, drop popularly after science had established its capabilities. from between your finger the plaster into it, pour off Even now, it is one of those practical improvements the superfluous water, and then stir it gently; take a which, to a certain extent, remain under public suspihog-hair brush and brush a portion of the plaster well cion. Twelve years ago, Dr Ritchie made some atinto the subject, then pour as much as will make the tempts to complete the plan of an electric telegraph; required thickness. Coins and medals can be readily Sir Humphry Davy and others also engaged in a similar copied by means of sealing-wax impressions; if the undertaking. In 1837, the model of an apparatus for reef be very prominent, they are best attained from communicating by galvanic action, was exhibited by plaster casts; a coin can be silvered, or gilt, as here- Mr Alexander before the Society of Arts in Edinburgh; after described, or bronzed, by brushing it well with and this, as far as we know, was the first time the thing black-lead, then making it hot, and again brushing it. was brought in a tangible form before the public. Mr Various degrees of heat will give different tints; should Alexander's telegraph was in the form of a chest, conthe first attempt not give satisfaction, it may be well taining thirty copper wires, answering to the twentywashed with hot water and soap, and the process re-six letters of the alphabet, three points, and an asterisk pested. Having well black-leaded a wood-engraving, to denote the termination of a word. At one end, in take a strip of tin-foil, and bind it close round the sides, connexion with the wires, were keys like those of a carefully pressing the edge all round, to bring it in piano-forte, and underneath these were a pair of plates, contact with the black-leaded surface; then, with the zinc and copper, forming a galvanic trough at the wire attached to the zinc, which being long enough to other extremity of the wires were thirty steel magnets, surround the whole, bind it tight, and varnish as be- and, any one of these being affected by the electric fore. Wood, from its buoyancy, will float, unless a agency produced by touching the key, it was turned to árm, stout wire be used to retain it in its vertical posi- the right or left, and unveiled a particular letter. On Lon, which is essentially requisite; for, if it incline at removing the finger from the key, the magnet sprung an angle, with the lower part at the greatest distance back, and the letter was screened from observation. from the zinc, the new deposit will be formed in ridges. Thus any letter could be instantaneously exposed, or After this has once occurred, it will be impossible to words spelled letter by letter, according to the will of obtain an equal deposit; because the copper accumu- the operator. As galvanism requires a complete circuit lates only on the most prominent parts, and the hollows for its operation, it might be supposed that a duplication remain proportionately thin, as at the first deviation of the thirty wires would have been necessary, but by from an equal surface. This applies to every kind of a happy arrangement of Mr Alexander, with one return deposit, whether seals, medals, or copper plates. A wire to serve for all, this encumbering of the apparatus similar result will also take place in a weak solution, or was avoided. ma deep trough, from the liquid losing its particles of copper, and becoming lighter, rising in a regular channel to the surface; the deep trough giving space for a descent of the denser portion of the liquid containing the metal in solution. These copies from wood-enravings have an advantage above the ordinary profor obtaining duplicates for printing, being made perfect direct from the wood, whereas the stereotype copies frequently require re-touching by the engraver, rising from the friability of the plaster from which they are cast."

Mr Smee, whose researches in electro-galvanism are wal known to the philosophical world, has suggested a still more extraordinary kind of electrotyping, namely, the making a copperplate engraving without an engravag in the first instance. He describes it in a paper in Philosophical Magazine, No. 105, from which we extract the following passage :-" First, draw the requred subject upon a smooth copper plate, with any thick varnish or pigment insoluble in water, and then pose the plate in the usual way to the influence of current, when first copper will be thrown down apon the uncovered parts and will gradually grow over the drawing, and the electrotype, when removed, will be ready for printing. Very thick oil paint should be ed, else sufficient depth will not be obtained to hold mk. As an additional advantage to its cheapness, this method does not require the artist to reverse the gn. An opposite effect to this may be produced by placing a piece of copper similarly drawn upon at the ygen end of the battery, when the metal will be acted on, leaving a drawing in basso-relievo." Electric Telegraphs.—Galvanism, and its twin-prine electro-magnetism, have performed other wonders application to the arts. One of the most interesting their powers in this respect, is that of transmitting telegraphic signals through wires to any assignable distance. The general principle on which such an operation founded, is that of causing the galvanic current to defeet or turn a needle poised on a centre, and by certain arrangements the needle is made to point to any letter adial-plate. The discovery of this kind of telegraphic action is by no means new. From a passage in Arthur Young's Travels in France, published in 1787, it appears to have been at that period known, and to some extent practised, by a M. Lomond. But like many other re

Since this time, considerable improvements have been effected on the mechanism of electric telegraphs, by Professor Wheatstone and Mr Cook, one material object having been the reduction of the number of wires, which has been effected with a surprising degree of skill. A writer in Chambers's Edinburgh Journal (July 25, 1840) thus describes what he saw of the process on the occasion of a visit to the professor's classroom at King's College, London:-"The professor showed two varieties of the apparatus, one being the latest invention, and the most deeply interesting from its simplicity. It may be briefly described as consisting of two small galvanic troughs or batteries; four lengths of copper wire; an object resembling a brass clock, with a small opening or dial on the surface sufficient to show a single letter at a time; close by this case of mechanism stood an upright pivot of brass about three inches high, having a circular top inscribed with the letters of the alphabet all round, and from each letter a spike pointing outwards like the spokes from a capstan. The whole stood on a table, except the wires, which, being four miles in length, and warped in numerous convolutions through the vaults of the college, were observable only at their extremities in connexion with the apparatus.

With respect to the principle of the process, it will suffice to state, that the electricity or galvanic property generated in the batteries, was made to proceed along the wires, and in its passage to affect the mechanism in the case. In the construction of this mechanism, the great merit of the invention consists. It is a beautiful combination of brass wheels, and other details, the object of which is to produce a desired letter or figure at the exterior opening or dial. To bring any particular letter into view, the capstan is turned by the finger till the metal point projecting from a similar letter upon it, is made to touch a corresponding point near the side of the case. Thus, there is a sympathy, as I may call it, between the letters in the case and the letters on the capstan. A touch of the point opposite L, will bring L into view on the dial, and so on with any other letter. Nothing can be more perfect, or apparently simple. To appearance, the letters can be exposed at the rate of two in every moment of time. A lady, turning the capstan with her finger, brought into view the word London, in the time it could be uttered letter by

It being thus ascertained, by practical working, that the electric telegraph can perform all that its designers have proposed, it only remains that it should be spread in different directions over the country, or at the least laid in communication from London along the great lines of thoroughfare.

The method of working the apparatus will be readily understood. At each extremity of the line of rope for it would work both ways-there would be an office for receiving and communicating intelligence, at a price conformable to the extent of the message. Being dispatched from one end, the communication would be instantaneously received at the other by an officiating clerk, and forthwith made known by a note to the party concerned. Thus, intelligence of the rise and fall of stocks, foreign news, orders for goods, or any other species of communication of an urgent nature, might, with the utmost facility, and at a trifling cost, be transmitted to any imaginable distance."

letter, although the idea had to travel through four | It is the intention of the Great Western Railway Commiles of wire. pany to carry the tube along the line as fast as the In the transmission of the electric influence through completion of the rails takes place, and ultimately the wires of this or any other apparatus, distance is of throughout the whole distance to Bristol. The machi no consequence as respects time, for electricity is sup-nery, and the mode of working it, are so exceedingly posed, with some degree of probability, to travel with simple, that a child who could read would, after an the velocity of light, or 192,000 miles in the space of a hour or two's instruction, be enabled efficiently to transsecond. In point of fact, therefore, no longer time mit and receive information.' would be occupied in transmitting intelligence to the uttermost ends of the earth, than would be required for sending it across a room or a table. Distance is a matter for consideration only as regards expenditure of galvanic force. The electric agency has a tendency to weaken in its progress, according to circumstances, and this must necessarily be provided for by increasing the number of batteries to the desired amount and power. It has been supposed that the difficulty of perfectly isolating and preserving the wires from injury in their course, would be an insuperable bar to their establishment on an effective footing; but fears need be no longer entertained on this score. Each of the four wires in the above apparatus, is wrapped round with a well-rosined thread, and the whole are then tied together with a cord possessing a similar coating, so as to present the appearance of a tightly-bound rope. This it is proposed to place in a small iron tube, like that used for bringing gas into houses, and the tubes, united to any length, are laid below the ground, or in a wooden case on the surface, to preserve them from injury. Yet another difficulty here presents itself. What if the rope, or any particular wire, should be fractured somewhere in its course? How would the precise point of injury be discoverable? This the professor has likewise provided for, as far as it possibly He proposes that there shall be a signal-case val of every few miles along the whole line, and therefore should any injury be sustained by the wires, it will be speedily discovered in what portion it has taken place, and a new and complete section of rope inserted in connexion with the other pieces. To avoid a very remote chance of delay in the transmission of intelligence from this cause, it would be easy to lay two sets of wires, one of which could be employed while the other was in course of being repaired.

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Still more lately the galvanic principle has been applied to the regulation of clocks, with a view to preserve a uniformity of motion in all the clocks in a town, or in a public office, to which wires may be led. The manner in which this is accomplished is now (or was lately) exhibited at the Polytechnic Institution in London.

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ELECTRO-MAGNETISM.

BEFORE noticing this electric quality, it seems necessary to give a short explanation of Magnetism, or the preperties of the Magnet. Anciently, there was found in Magnesia, in Asia, a certain kind of iron ore, in which the remarkable property was discovered of attracting other kinds of iron or steel; this ore afterwards reThe capabilities of the principle have been fully ceived the name of loadstone, but from Magnesia, the tested in a practical manner on the line of the Great place in which it was originally found, we derive the Western Railway. In September 1839, when the wires terms magnet and magnetism. Latterly, loadstone ore of the electric telegraph were carried as far as West has been discovered in Siberia, Sweden, Piedmont, the Drayton, a distance of fifteen miles, the following ac- kingdom of Naples, and various places in North Ame count was given of it in one of the London papers :- rica. This magnetic iron ore, which is of an excellent The space occupied by the case containing the ma-quality for making steel, is of a dark colour, and genechinery (which simply stands upon a table, and can be rally occurs crystallised in the form of regular octaremoved at pleasure to any part of the room) is little hedrons; its attractive quality is strengthened by exmore than that required for a gentleman's hat-box. The posure to the air. It has likewise been found that telegraph is worked by merely pressing small brass meteoric stones, which are composed of iron and nickel, keys (similar to those of a keyed bugle), which, acting possess a strong magnetic virtue resembling the loadby means of galvanic power upon various hands placed stone of the earth. upon a dial plate at the other end of the telegraphic line, as far as now opened, point not only to each letter of the alphabet (as each key may be struck or pressed), but the numerals are indicated by the same means, as well as the various points, from a comma to a colon, with notes of interrogation and interjection. There is likewise a cross (+) upon the dial, which indicates that where this key is struck, a mistake has been committed in some part of the sentence telegraphed, and that an erasure is intended. To a question-such, for instance, as the following: "How many passengers started from Drayton by the ten o'clock train?"-the answer could Independently of attracting iron, magnets possess the be transmitted from the terminus to Drayton and back extraordinary property of polarity. When a small mag in less than two minutes. This was proved on Satur-netic bar is poised at the centre, so as to be free to move day. This mode of communication is only completed in any direction, one end points towards the north pole as far as West Drayton station, which is about 13 of the earth and another towards the south. It is true, miles from Paddington. There are wires (as may be there are variations in the direction at different parts imagined) communicating with each end, thus far com- of the globe, but with these slight exceptions, the mag pleted, passing through a hollow iron tube, not more netic needle, as it is called, offers one point to the north than an inch and a half in diameter, which is fixed and another to the south. Hence the application of the inches above the ground parallel with the compass to navigation. (See the Article OCEAN.) From about two or three feet distant from it. what will be immediately mentioned, no room is left for

Although the ancients were acquainted with the attractive property of the loadstone, it was left for the moderns to discover that the property could be commu nicated to the iron which the magnetic stone attracted. Since this important discovery was made, artificial magnets, composed of bars or slips of iron, have been easily constructed; and these possess all the attractive virtues of the loadstone itself. Besides iron, a few other metals are susceptible of being attracted, such as pure cobalt and nickel; but the power is weak and of no avail in the arts.