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pointed inetallic substances. These things being here particularly refer were made under the observed, place a few pointed wires in the prime direction and superintendence of Mr. Watson, conductor of the machine; put the machine in who, as an eye-witness of them, drew up the action, and after the lapse of a few minutes the account to lay before the Royal Society. air of the room will become so impregnated with 391. The first attempt of these electricians electricity as to be very perceptible to the sense was to convey electric shocks across the river of smelling, and will readily affect a delicate Thames, availing themselves of the water of the electrometer, particularly if brought into the river as one part of the circuit through which the vicinity of the machine. The odor perceived on charge was to pass. This they accomplished on this occasion very much resembles that of oxygen the 14th and 18th of July, 1747, by fastening a gas, or of the atmospheric air in a very clear and wire all along Westminster-bridge, at a considerfrosty night.
able height above the water. One end of this 387. The charge of a jar is retained in the wire communicated with the coating of a charged electric.—This is proved in a very satisfactory phial, the other being held by an observer, who, manner by the following experiments, which in his other hand, held an iron rod, which he show that the coating of the Leyden jar has not dipped into the river. On the opposite side of quite so inuch to do with the charge as is gene- the river stood a gentleman, who likewise dipped rally supposed. The first is given by Mr. an iron rod in the river with one hand; and in Walker in his System of Familiar Philosophy, the other held a wire, the extremity of which ard is ira substance as follows :-Lay a plate of might be brought into contact with the wire of un or brass on your hand, and on it a plate of the phial. glass (rather larger than the metallic plate); on 392. When the discharge was made, the shock the glass lay another metallic plate, and let this was distinctly felt by the observers on both sides communicate with the prime conductor: 'thus of the river, but more sensibly by those who the glass may be charged. By the edge of the were stationed on the same side with the maglass disengage it from the two plates, and place chine; part of the electric fire having gone from two other plates in the same situation, upon and the wire down the moist stones of the bridge, under the glass. If now one knob of the dis- thereby making several shorter circuits to the charging-rod be made to touch the under plate, phial, but still all passing through the gentlemen and the other knob the upper plate, a discharge who were stationed on the same side with the will ensue the same as if the first plates had machine. This was, in a manner, demonstrated remained in their place.
by some persons feeling a sensible shock in their 388. The same principle is tnus illustrated by arms and feet, who only happened to touch the the Leyden jar; we give the process as directed wire at the time of one of the discharges, when by Mr. Singer :-Procure a jar with a double set they were standing upon the wet steps which led of moveable tin-coatings, either of which may be to the river. In one of the discharges made adapted to it at pleasure; the outer coating being upon this occasion, spirits were kindled by the a tin can large enough to admit the jar easily fire which had gone through the river. The within it; and the inner coating a similar can gentlemen made use of wires in preference to sufficiently small to pass readily in the inside of chains, as communicating a stronger degree of the jar. The charging wire of the inner coating electricity. should be surrounded by a glass tube covered 393. Their next attempt was to cause the elecwith sealing-wax, to serve as an insulating han- trical fluid to make a circuit of two miles, at the dle, by which the inner coating may be lifted New River at Stoke Newington. This they perfrom the jar when that is charged, without com- formed on the 24th of July, 1747, at two places; municating a shock to the operator. Arrange at one of which the distance by land was 800 the jar with its coatings, and charge it; it will feet, and by water 2000: in the other, the disact in every respect as an ordinary coated jar. tance by land was 2800 feet, and by water 8000. Charge the jar, and, without discharging it, The disposition of the apparatus was similar to remove the inner coating by its insulating handle; what they had before used at Westminsterif this coating, when removed, be examined, it bridge, and the effect answered their utmost will be found not at all, or but slightly electri- expectations. But as, in both cases, the observfied : lift the jar carefully from within its outer ers at both extremities of the chain, which tercoating, and examine that; it will evince nominated in the water, felt the shock as well signs of electricity.
when they stood with their rods fixed into the 389. Let the jar be now fitted up with the earth twenty feet from the water, as when they other pair ot moveable coatings; apply the dis- were put into the river; it occasioned a doubt, charger, and an explosion and spark will follow, whether the electric circuit was formed through which clearly proves that the accumulation is the windings of the river, or a much shorter way, retained by the attractive power of the glass, and by the ground of the meadow; for the experithat the coatings are only useful as conductors ment plainly showed that the meadow-ground, to the charge.
with the grass on it, conducted the electricity 390. Velocity of the electric fluid.-Although very well. we have already made some passing remarks on 394. From subsequent experiments they were this subject, the following detail will, we doubtfully convinced that the electricity had not in not, be found interesting to the admirers of the this case been conveyed by the water of the electrical science. Sereral electricians of dis- river, which was two miles in length, but by land, tinguished merit made experiments on the where istance was only one mile; in which velocity of the electric fluid; those to which we space, however, the electric matter must neces
sarily have passed over the New River twice, tricity and sound. For this purpose they fixed and bave gone through several gravel-pits, and a upon Shooter's Hill, and made their first expelarge stubble-field.
riments on the 14th of August, 1747; a time 395. On the 28th of July, they repeated the when, as it happened, but one shower of rain experiment at the same place, with the following had fallen during five preceding weeks. The variation of circumstances :—The iron wire was, wire communicating with the iron rod which in its whole length, supported by dry sticks, and made the discharge, was 6732 feet in length, and the observers stood upon original electrics; the was supported all the way upon baked sticks : effect was, that they felt the shock much more as was also the wire which communicated with sensibly than when the conducting-wire had lain the coating of the phial which was 3868 feet upon the ground, and when the observers had long, and the observers were distant from each likewise stood upon the ground, as in the former other two miles. experiment. Afterwards, every thing else re 400. The result of the explosion demonstrated maining as before, the observers were directed, to the satisfaction of the gentlemen present, that instead of dipping their rods into the water, to the circuit performed by the electric matter was put them into the ground, each 150 feet from four miles, viz. two miles of wire and two of dry the water. They were both smartly struck, ground, the space between the extremities of the though they were distant from each other above wires; a distance which, without trial, as they 500 feet.
justly observed, was too great to be credited. Å 396. Their next object was to determine whe- gun was discharged at the instant of the explother the electric virtue could be conveyed through sion and the observers had stop-watches in their dry ground; and, at the same time, to carry it hands, to note the moment when they felt the through water to a greater distance than they had shock: but as far as they could distinguish, the done before. For this purpose they pitched upon time in which the electric matter performed that Highbury Barn, beyond Islington, where they vast circuit might have been instantaneous. In carried it into execution on the 5th of August, all the explosions where the circuit was made of 1747. They chose a station for their machine considerable length, it was observed that though almost equally distant from two other stations, the phial was very well charged, yet that the fur observers upon the New River, which were snap at the gun barrel, made by the explosion somewhat more than a mile asunder by land, was not near so loud as when the circuit was and two miles by water.
formed in a room: so that a by-stander, says 397. They had found the streets of London, Dr. Watson, though versed in these operations, when dry, to conduct very strongly for about would not imagine from seeing the flash, and forty yards; and the dry road at Newington hearing the report that the stroke at the extremity about the same distance. The event of this trial of the conducting wire could have been consianswered their expectations. The electric fire derable; the contrary whereof, when the wires made the circuit of the water, when both the wêre properly managed, he says, always hapwires and the observers were supported upon pened. onginal electrics, and the rods dipped into the 401. Still, these philosophers were desirous to river. They also both felt the shock, when one ascertain the absolute velocity of electricity at a of the observers was placed in a dry gravelly pit, certain distance; because though in the last exabout 300 yards nearer the machine than the for- periment, the time of its progress was certainly mer station, and 100 yards distant from the river: very small, if any, they were desirous of knowfrom which the gentlemen were satisfied, that ing, small as that time might be, whether it was the dry gravelly ground had conducted the elec- measurable: and Dr. Watson had contrived an tricity as strongly as water.
excellent method for that purpose. Accordingly, 398. From the shocks which the observers re on the 5th of August, 1748, the gentlemen met ceived, when the electric power was conducted once more at Shooter's Hill; when it was agreed upon dry sticks, they were of opinion, that, from to make an electric circuit of two miles, by sethe difference of distance simply considered, the veral turnings of the wire in the same field. The force of the shock, as far as they had yet expe- middle of this circuit they contrived to be in the nenced, was very little if at all impaired. When same room with the machine, where an observer they stood upon electrics, and touched the water took in each hand one of the extremities of the on the ground with the iron rods, the shock was wires, each of which was a mile in length. In always felt in their arms or wrists; when they this excellent disposition of the apparatus, in stood upon the ground, with their iron rods, they which the time between the explosion, and the felt the shock in their elbows, wrists, and ankles; shock might have been observed to the greatest and, when they stood upon the ground without exactness, the phial was discharged several rods, the shock was always felt in the elbow and times ; but the observer always felt himself wrist of that hand which held the conducting shocked at the very instant of making the explosre, and in both arkles.
sion. Upon this the gentlemen were fully satis399. The last investigation which these gen-fied, that through the whole length of this wire, tlemen made on this subject, and which required which was 12,276 feet, the velocity of the elecall their sagacity and address in the conduct of tric matter was instantaneous. it, was to try whether the electric shock was per 402. Notwithstanding all this surprising veloceptible at twice the distance to which they had city, it is certain, that both sides of a charged before carried it, in ground perfectly dry, and phial may be touched so quickly, even by the where no water was near; and also to distin conductors, tha the electric ma had guish, if possible, the respective velocity of elec- not time to make the circuit, and the phial will
remain but half discharged. If the upper plate state of equilibrium in them, and becomnes diof an electrophorus also is very suddenly touched vided among them in proportion to their form, with the finger, or any other conductor, a very ard principally to their extent of surface ; and small spark will be obtained on lifting it up; that hence a body that is charged with the fluid though a very strong one would be got if the fin- being in communication with the immense sur-, ger was kept longer upon it. But how this seem- face of the earth, will retain no sensible portion ing slowness can be reconciled with the immea- of it. surable velocity above mentioned, does not ap 407. Gay Lussac defines a paratonnerre to be pear. It is certain, indeed, that this fluid is a conductor which the electric matter prefers to considerably resisted in its passages through or the surrounding bodies, in order to reach the over every substance. It will even prefer a ground, and expand itself through it; and comshort passage in the air where it is violently re- monly consists of a bar of iron elevated on the sisted to one along a wire of very great length; buildings it is intended to protect, and descendo but here, as in every other case, it seems to di- without any divisions or breaks in its length, vide its force, and to break through several dif- into water or moist ground. When a paratonferent passages at once.
nerre has any breaks in it, or is not in perfect 403. The ainazing velocity of the electric fluid communication with a moist soil, the lightning, has recently given rise to some speculations on having struck it, flies from it to some neighthe subject of constructing electrical telegraphs; bouring body, or divides itself between the this idea, however, appears altogether chimerical, two, in order to pass more rapidly into the as has been proved by some experiments made earth. hy professor Barlow, of the Royal Military Aca 408. The most advantageous form that can be demy. By einploying wires of different lengths given to the extremity of a paratonnerre is that up to 840 feet, and measuring the energy of the of a sharp cone, and the higher it is elevated in electric action by the deflection produced in the the air, other circumstances being equal, the magnetic needle, he found that the intensity ra more its efficacy will be increased, as is proved pidly diminishes, and very nearly as the inverse by the experiments of M.M. de Romas and square of the distance. Mr. Barlow also ascer Charles. tained that the effect was greater with a wire of 409. It has not been accurately ascertained a certain size than with a finer one; but at the how far the sphere of action of a paratonnerre same time, that no advantage was gained by in- extends; but, in several instances, the more recreasing the diameter beyond a certain limit. mote parts of large buildings on which they have
404. We have thus gone through what we been erected, have been struck by lightning at consider as the essentials of electricity in ge- the distance of three or four times the length of neral; we have omitted several things which we the conductor from the rod. According, howconsider as heing now shsolete, and some also ever, to the opinion of Charles, a paratonnerre that are of too triflirg a nature to deserve a place will effectually protect from lightning a cirin any work pretending to respectability. It has cular space, whose radius is twice that of the been our aim to produce the most useful infor- height of the conductor. By increasing, theremation on every part of the subject, and to give fore, the altitude of a conductor, the space alsthe whole as much interest and life as the nature which it will protect is augmented in pre of a subject, purely philosophical, would admit. portion. It may, however, be adviseable, prior to closing 410. A current of electric matter, whether the present article, to furnish our readers with luminous or not, is always accompanied by heat, the latest facts in the science of electricity, and the intensity of which depends on the velocity many that follow are discoveries that are due to of the current. This heat is sufficient to make a the period that we are now writing.
metallic wire red hot, or to fuse or disperse it,
if sufficiently thin; and hence we may perceive ON PARATONNERRES, OR CONDUCTORS OF
the absurdity of some attempts which have been LIGHTNING.
lately made, to protect ships, by thin slips of 405. A very interesting report on the subject copper nailed to the masts. The heat of the of paratonnerres, has been presented to the Royal electric fluid scarcely raises the temperature Academy of Sciences by M. Gay Lussac. The of a bar of metal, on account of its large paper is divided into two parts ; one theoretical, mass; and no instance has yet occurred of an and the other practical, and the information con- iron bar, of rather more than half an inch tained in it may be reg led as the most perfect square, or of a cylinder of the same diameter, we possess on the subject.
having been fused, or even heated red hot by 406. The theoretical part is introduced with lightning. A rod of this size would, therefore, come general observations on electric matter, and be sufficient for a paratonnerre; but, as its stem of conductors ; that its velocity is at the rate of should rise from fifteen to thirty feet above the about 1950 feet per second ; that it penetrates building, it would not be of sufficient strength bodies, and traverses their substance, with un at the base to resist the action of the wind, equal degrees of velocity; that the resistance of unless it were made much thicker at that part. a conductor increases with its length, and may An iron bar, about three-quarters of an inch. exceed that which would be offered by a worse is sufficient for the conductor of the paratonbut shorter conductor; and that conductors of nerre. small diameter conduct worse than those of 411. According to Gay Lussac, a paratonlarger. The electric matter also tends always to nerre consists of two parts, the stem which prospread itself over conductors, and to assume a jects in the air above the roof, and the conductor,
which descends from the foot of the stem to the with bakers' ashes, rammed down as hard as ground. The stem he proposes to be a square possible, all round the conductor. In a dry soil, bar of iron, tapering from its base to the summit, or on a rock, the trench to receive the conductor in form of a pyramid, and for a height of from should be at least twice as long as that for a twenty to thirty feet, which is the mean length common soil, and even longer, if thereby it be of the stems placed on large buildings; the base possible to reach moist ground. Should the should be about two inches and a half square. situation not admit of the trench being much inIron being very liable to rust by the action of air creased in length, others, in a transverse direcand moisture, the point of the stem would soon tion, should be made, in which small bars of become blunt; and therefore, to prevent it, a iron, surrounded by ashes, are placed and conportion of the top, about twenty inches in length, nected with the conductor. In general, the should be composed of a conical stem of brass trench should be made in the dampest, and conor copper, gilt at its extremity, or terminated by sequently lowest spot near the building, and the a small platina needle, two inches long. In- water gutters made to discharge their waters over stead of the platina needle, one of standard it, so as to keep it always moist. Too great silver may be substituted, composed of nine precautions cannot be taken to give the lightning parts of silver, and one of copper. The platina a ready passage to the ground, for it is chiefly on needle should be soldered with a silver solder to this that the efficacy of a paratonnerre depends. the copper stem; and to prevent its separating 414. As iron bars are difficult to bend accordfrom it, which might sometimes happen, not- ing to the projections of a building, it has been withstanding the solder, it should be secured by a proposed to substitute metallic ropes in their small collar of copper. The copper stem is united stead. Fifteen iron wires are twisted together, to to the iron one,' by means of a gudgeon, which form one strand, and four of these form a rope, screws into each; the gudgeon is first fixed in about an inch in diameter. To prevent its rusting, the copper stem by two steady pins at right each strand is well tarred, separately, and, after angles to each other, and is then screwed into they are twisted together, the whole rope is tarred the iron stem, and secured there also by a steady over again with great care. Copper or brass
wire is, however, a better material for their con412. The conductor should be about three- struction than iron. If a building contain ary quarters of an inch square, and, as before stated, large masses of metal, as sheets of copper or reach from the foot of the stem to the ground. lead on the roof, metal pipes and gutters, iron It should be firmly united to the stem, by being braces, &c., they must all be connected with the tightly jammed between the two ears of a collar, paratonnerre, by iron bars of about half an inch by means of a bolt. The conductor should be square, or something less. Without this presupported parallel to the roof, at about six inches caution, the lightning might strike from the condistance from it, by forked stanchions, and after ductor to the metal (especially if there should be turning over the cornice of the building, without any accidental break in the former), and occasion touching it, should be brought down the wall, very serious injury to the building, and danger and to which it should be fastened by means of to its inhabitants. cramps. At the bottom of the wall, it is bent 415. Paratonnerres for Churches. — For a at right angles, and carried in that direction tower, the stem of the paratonnerre should rise twelve or fifteen feet, when it turns down into a from fifteen to twenty-four feet, according to its well.
area; the domes and steeples of churches, being 413. Since iron buried in the ground in im- usually much higher than the surrounding mediate contact with moist earth soon becomes objects, do not require so high a conductor as covered with rust, and is by degrees destroyed, buildings with extensive flat roofs. For the forthe conductor should be placed in a trough filled mer, therefore, their stems, rising from three to with charcoal, in the following manner. Having six feet above the cross or weather-cock, will be made a trench in the earth, about two feet deep, sufficient, and being light they may easily be a row of bricks is laid on their broad faces, and fixed to them without injuring their appearance, on thern cthers on edge; a stratum of bakers' or interfering with the motion of the vane. ashes (bra se de boulanger) is then strewed over 416. Paratonnerres for Powder-Magazines.-the bottom bricks, about two inches thick, on These require to be constructed with the greatest which the conductor is laid, and the trough then care. They should not be placed on the buildfilled up with more ashes, and closed by a row ings, but on poles at from six to ten feet disof bricks laid along the top. Iron thus buried tance. The stems should be about seven feet in charcoal, will undergo no change in thirty long, and the poles of such a height, that the Vears. After leaving the trough, the conductor stem may rise from fifteen to twenty feet above passes through the side of the well before alluded the top of the building. It is also advisable to to, and descends into the water to the depth of have several paratonnerres round each magazine. at least two feet below the lowest water line. If the magazine be in a tower, or other very lofty The extremity of the conductor usually termi- building, it may be sufficient to defend it by a mates in two or three branches, to give a readier double copper conductor, without any paratonpassage to the lightning into the water If there nerre stem. As the infinence of this conductor be no well at hand, a hole must be made in the will not extend beyond the building, it cannot ground, with a six-inch auger, to the depth of attract the lightning from a distance, and will about ten or fifteen feet, and the conductor passed yet protect the magazine, should it be struck. to the bottom of it, placing it carefully in the 417. Paratonnerres for Ships. The stem of a Curtre of the hole, which is then to be filled up paratonnerre for a ship, consists merely of a
coprer point, screwed on a round iron rod, 421. By certain changes of the surface, it was entering the extremity of the top-gallant mast. found that the inten ity of electricity produced An iron bar, connected with the foot of the was much affected. A plate of gold, plunged round rod, descends down the pole, and is ter in nitric acid for a few moments, and then washed minated by.a crook or ring, to which the con in several fresh portions of water, produced a ductor of the paratonnerre is attached, which, in development of electricity much greater than this case, is formed of a metallic rope, connected before, the water still becoming negative. The at its lower extremity with a bar or plate of same plate, plunged into
solution of potassa metal, and which latter is connected to the cop- and then washed, lost in a great measure its per sheathing on the bottom of the vessel. Small power of becoming electrified by contact with vesseis require only one paratonnerre; large A plate of platinum offered similar reships should have one on the main-mast and sults. It is supposed, that these effects may another on the mizen-mast.
have a distant analogy with the facts observed 418. The late ingenious Mr. George Sing r by M. M. Thenard and Dulong, that a new plain his excellent work on electricity, proposed to tina wire, which would not heat in a current of have conductors fixed to the surfaces of masts, lıydrogen gas and air, acquired this property and the electric fluid conveyed by means of by being previously plunged for a few minutes strips of metal, over the deck and the sides of in nitric acid, and then washed. The property the vessel ;
but this arrangement on many of the wire continued for above twenty-four accounts is highly objectionable, and the mode hours; and M. Becquerel says, that the plate of proposed by Gay Lussac, or perhaps that com- gold preserved its power of becoming strongly monly adopted in the British navy, of conveying electrified in contact with water, for several the electric fuid from the mast-head to the sur hours. face of the water, in a direct line, by means of a series of long copper links, is the best which has ON THE ELECTRICAL ACTIONS PRODUCED BY hitherto been devised.
THE CONTACT OF FLAMES AND METALS. 419. It is allowed from experiment, that the stem of a paratonnerre effectually defends a 122. In place of making a complete metallic circle of which it is the centre, and whose radius circuit, as in Seebeck's experiment; or one in is twice its own height. According to this rule, which the circuit was by water or acid, as in the a building sixty-feet square, requires only a Voltaic pile; the metals used were connected stem of fifteen or eighteen feet raised in the by a flame only, and their states ascertained centre of the roof. A building of 120 feet, by by the electrometer. The flames used were those the same rule, would require a stem of thirty resulting from the combustion of alcohol, hyfeet, and such are sometimes used; but it is drogen gas, or a sheet of paper. When a plate better, instead of one stem of that length, to of platina was placed on the cap of the elecerect two of fifteen or eighteen feet, one placed at trometer, and heated by one of the flames before thirty feet from one end of the building, the other mentioned, if the temperature was a red heat or at the same distance from the other end, and above, the metal became negative, but below a consequently sixty feet from each other. The red heat it became positive. On trying the elecsame rule should be followed for three or any tricity of the flame, by making it rise from a greater number of paratonnerres. A plate is piece of wet wood on the cap of the instrument, given in the Annals of Philosophy to illustrate and holding the platina in it, the reverse, as exthis interesting subject more particularly. pected, was found to be the case.
423. A copper wire gave the same results, ELECTRO-MOTIVE ACTION OF WATER ON
and generally it appeared that all the metals bad METALS.
the property just described ; thus any metal, 420. M. Becquerel has endeavoured to ascer- plunged into a fame of bydrogen gas, becomes tain experimentally the electrical effects pro- negative or positive according as the temperature duced by the contact of water and metals. The is higher or lower, and communicates the coneffect is so small as to be easily mistaken for, or trary electricity to the fame. confounded with, those due to electricity pro 424. If the fame by which the plate of metal duced accidentally during the performance of on the cap of the instrument is heated, be the experiments, by contact of various parts of touched by a piece of wet wood instead of being the apparatus, or in other ways: but taking insulated, the effects are more distinct : but every possible precaution, and testing his re- if, instead of touching it with wet wood, it sults in all ways, he arrived at the conclusion be touched with a plate of the same metal as that zinc, iron, lead, tin, copper, &c., communi- that on the electrometer, the two portions of cated positive electricity to water; whilst pla- metal are found in different states : that heated tina. gold, silver, &c., gave it negative electricity. to redness being negative, and the one heated to Water is therefore positive with the metals which a less degree positive. The same effects are are most positive, and negative with those which obtained if the two plates be of different inelala. are least positive. It operates, therefore, upon They are also produced if the flame urged by a oxidable metals as alkalies do in their conduct blow-pipe be used. with acids, when there is no chemical action. 425. These phenomena may be supposed to The same phenomena take place even when a result either from the friction of the flame on the little sulphuric acid is presert, and the iron and metals, or from an electro-motive action. M. zinc are acted upon, so that chemic ac in Becquerel inclines to the latter opinion, conceiving this case did not prevent the production of elec- it improbable that the tranquil Aame of alcrhol tricity by the contact of inetals and water can produce friction sufficient to suffice for the