Slectrome- wood, C, by which it is held in the hand; the other ter. end is clofed by a brafs cap, D; the diftance between the extremities of the fmall tube and that of the large one is filled with red wax, B, B; on the cap Dis fcrewed at pleasure, either a ring E, or a brafs hook F. The ring is ufed for applying the inftrument to the ball of a conductor, and the hook when it is hung to a ring on the cap D is a brass stem G, terminating by a knob. This ftem is bended, and the extremity of its knob must be directly beneath the line with which the graduated scale of the fmall tube com

mences.

Round the large tube is a brass-ring H, half of which extends to the length of twelve or fifteen lines in the form of a half tube P, applied against the fides of the tube. This gutter ferves to mark the degrees, by fliding along the graduated scale by means of a button beneath I. On the ring H is fixed one of the fmall electrometers invented by Sauffure, K, K, which is furmounted by a ftem V, on which stem is fixed at pleasure either a point L, or a ball M, of the fame fize as that which terminates the ftem G, oppofite which it is placed. The extremity of this point or ball must be placed immediately over the extremity of the half tube or fcale P, and horizontally to the centre of the ball, which terminates the ftem G.

At the top of Sauffure's electrometer is a small ring N, which ferves to connect it with the chain Z when required.

To explain the use of this inftrument by a fingle experiment, charge a Leyden jar, till the fpontaneous overflowing announces it to be faturated. Then place the ring E on the knob of this bottle, and cause the electrometer of Sauffure, armed with its point, to slide towards it. Obferve the degree at which the divergence of the thread ftream commences, and at that inftant suppress the point, and adapt in its place the ball M. Continue to advance the electrometer of Sauffure till the electric preffure of the atmosphere in the jar caufes the threads to diverge; again obferve the degrees, replace the point L, and close the shutters of the room; then continue to advance the electrometer till the luminous point appears, which again affords new degrees. Lastly, replace the ball M, and fix the chain Z to the fmall ring N; cause it to communicate with the exte rior coating of the jar, and advance the electrometer till the explofion takes place. Then comparing the different degrees, we may afcertain the comparative difference between the refpective methods.

As foon as thefe relative proportions have been once accurately ascertained by attentive obfervations, one of thofe methods alone will be fufficient for meafuring the intensity of electricity; and, in fact, if the body intended to be fubmitted to examination be little charged with the electric fluid, the diverging of the threads, by means of the point, will fix the limits of the electric atmofphere: if it be more, the preffure of the atmosphere on the ball M, which is fubftituted for the point, will indicate this quantity. In fhort, if the body be loaded with a confiderable mafs of electric matter, it will be fhown by the luminous point. If a Leyden jar, instead of being pofitively, is negatively electrified, the point indicates it at the fame time that it measures the elec. tric atmosphere, for instead of a luminous point, a ftar

will be obferved upon the ball of the jar, and another Electromeat the end of the point.

Let us now apply this electrometer to useful obfervations.

In order to connect the idea of a determinate quantity of fluid to each degree of the electrometer, it is neceffary to compare thefe degrees with the known quantities. Suppofe for inftance we have a jar, the coating of which is fix inches fquare; electrify it till a fpontaneous discharge takes place, and remark, by means of Henley's electrometer, at what degree this difcharge is effected. Again, electrify the jar, till it is nearly faturated, and measuring with this electrometer, obferve, that the luminous point appears for inftance at two degrees; then fay, that when the electrometer, applied to an electrified body, marks two degrees, the body contains fix inches fquare of electricity. Repeat this experiment with a plate of glafs, the coating of which is feven, eight, ten, or twelve fquare inches, and we may form a fcale of proportion, which is of the greatest utility in accurate experiments.

"In endeavouring to afcertain fome of these propofitions, (fays M. Cadet), I have made an obfervation which has convinced me of the utility of my electrometer in difcovering the capacity of electric apparatus. Having taken a jar from an electric battery, I electrified it, and measured it with a point which I paffed along a string of filk; on obferving the distance at which the luminous point appeared, I joined this jar to another of the fame fize, and imagined that by doubling the quantity of matter, the measure I had taken would alfo be doubled; on the contrary, however, the latter measure was not more than about one-third of the former I then added a third bottle; and ftill obtained nearly the fame refult; whence the following propofition appears to be established; namely, that the extent of the electric atmosphere is in an inverfe ratio to the quantity of fluid accumulated, Another obfervation which I have feveral times made, on measuring the electric atmosphere of a conductor, is, that the limits of this atmosphere form an elliptic figure around the body, nearly fimilar to that reprefented at fig. 7.

"This doubtlefs arifes from the electrified body fufpended in a chamber, being nearer to the earth than the ceiling; but it would be a curious experiment to measure it at an equal diftance from every attracting body, in order to obferve whether the fluid has not really a tendency to defcend towards the earth, rather than in any other direction. It is my intention to repeat this experiment, as I confider it of great importance to afcertain whether electricity gravitates towards the globe.

"From these first attempts, I conceive my electrometer would be well adapted for meafuring the abfolute capacity of Leyden jars, and alfo their capacity with regard to their fize, or to the quality of the glafs of which they are conftructed; for the latter, by its greater or lefs denfity, abforbs a greater or lefs quantity of fluid."

IV. Lawson's ELECTROMETER. This is a fimplified improvement on Brooke's fteelyard electrometer, and fhould have been defcribed when that inftrument was mentioned, instead of Mr Adams's; but it did not occur, to us till after that sheet was printed.

The

ter.

Fig. 7.

Electrome

ter.

Fig. 8.

"Some time ago it ftruck me that fome additions to Brooke's electrometer might be made, so as to fit it for a good discharging electrometer to measure the repulfion between two balls (of a certain fize) in grains, and alfo effect the difcharge of a battery at the fame time. The inftrument known by the name of Cuthbertfon's dif charging electrometer, (See ELECTRICITY, N° 203.) was at that time the beft, and indeed the only inArument for discharging batteries or jars by its own action, then made; but I think this will be found, in the essentials, and in the theory and ufe, a more perfect inftrument.

"On the bafis (fig. 8.) is fixed the glafs pillar G, fupporting the hollow brass ball B. I is a light graduated brass tube, divided (from the weight W towards the ball B) into 30 parts, reprefenting grains. W is a fliding weight. L, a light brafs ball fcrewed to the end of the tube I. On the other end of which tube adjusts the heavy counterbalance ball C, the tube I and its two balls being fufpended at their common centre of gravity by a filk line in the centre of the ball B, the mechanifm of which is fhewn in fig. 9. The brafs ball F is ftationary, and of the fame fize as the ball L; and is fixed by, and adjusts close to, the ball L, or at any lower ftation between that and the ring r. The brass tube to which the ball A is fixed is divided into inches, halves, and quarters: (a more minute divifion is unneceffary and improper). The divifions begin, or the line o is marked on the faid tube at the ring r, when the three balls A, L, F, are close together. The ring r serves as an index, as the divifions pafs in fucceffion into the glass tube P on lowering the ball A. The hook H is fcrewed into the bafe of P. The quadrant, or Henley's electrometer, Q, is fupported in a long brafs ftem, to keep it out of the atmosphere of the lower part Fig. 9. of the inftrument. Fig. 9. fhows the internal conftruction of the ball B, fig. 8. In the first place the ball fcrews in half, horizontally. The light tube I paffes through the ball, and is fufpended nearly in the centre of it by fome filk twift, s, which small filk twift is fixed into the eye of the adjufting wire, a, part of which wire is filed fquare and goes through the fquare hole h. The nut n fcrews on a, and ferves to adjust the light tube I vertically. The light plates PP are of copper, and move freely on the wire w w fomewhat like a hinge, and reft on the copper wires CC, ferving to make the direct communication between the infide and out of the battery or jar. NN are notches ferving to let the tube I defcend when the discharge is made. Into the tube Z the glafs pillar is ground. Note, that at the bottom of the notch N is a piece of brafs filled with a Y, and fo placed as to keep the centres of the balls L and F, fig. 8. under each other when they come close together.

"When the inftrument is adjusted, which is done by placing the weight W, fig. 8. at o on the line of grains, and then forewing or unfcrewing the counterbalance ball C, till the tube I rifes flowly into its horizontal pofition; then fet the ball A at the diftance from the ball L that you choose, and the weight W placed at the divifion or number of grains that you with the repulfive power of the electricity to arrive at before the difcharge

V. Hauch's ELECTROMETER. Fig. 10. contains a re- Fig. 10. prefentation of this electrometer, and the different parts of which it confifts. OP is a board of dry mahogany, twelve inches in length and four in breadth, which ferves as a fland for the inftrument. In this board are faftened two maffy glafs pillars, M and N, which fupport the two brafs caps or rings GG, with the two forks of tempered fteel KK fcrewed into them. The two rings GG are well covered with varnish.

In the ring is fastened a brass rod, which terminates in a ball E of the fame metal, and an inch in diameter. The length of the rod and ball together is four inches and a half.

A very delicate beam AB, the arms of which are of unequal length, moves on a short triangular axis (a knife edge) of well tempered fteel, on the fork K of the pillar M. It is feventeen inches in length, and so constructed that the short arm forms a third, and the long one twothirds of the whole beam. The short arm of brafs fur. nifhed with the ball B, exactly of the fame fize as the ball E, is divided into forty-five parts equivalent to grains. The long arm A is of glafs covered with copal varnish, and ends in an ivory ball A, into which is fitted an ivory hook R, deftined to fupport the ivory fcale H. In order to render the infulation more complete, this scale is sufpended by three hairs.

A very delicate beam CD, eleven inches in length, moves on an axis like the former, on the pillar N, though not here fhewn. This beam is proportioned in the fame manner, one arm being a third and the other two-thirds of the whole length. The long arm of brafs is furnished at the end with a ball D, and divided into thirty parts correfponding to grains. The fhort arm of glafs terminates in a long roundish plate C, covered with copal varnish. The fteel forks are fhewn by the fections of the two brafs caps FF, as are alfo the two knife edges L, L. By these caps the escape of the electric matter is partly prevented.

A brafs ring Q, capable of being moved along the fhort arm of the upper beam AB, fhews by means of marks determined by trial and cut out on the beam, the number of grains which must be placed in the fmall fcale to reftore the equilibrium of the beam, at each distance of the ring Q from the point of fufpenfion.

On the long arm CD of the lower beam there is alfo a moveable ring S, which, like the ring Q, fhews in grains, by its diftance from the point of fufpenfion, the power requifite to overcome the preponderance of LD in regard to LC.

The power neceffary for this purpose will be found, if

the

ter.

Electrome- the shell H, which weighs exactly fourteen grains, be fuffered to fink down on the glafs plate C, and the ring s be pushed forwards till both the arms of the beam are in equilibrium. The part of the beam on which the rings has moved, is divided into fourteen parts, fo that marks the place where the ring s muft ftand when the beam, in its free flate, is in equilibrium; and 14 ftands at the place where the rings again reftores a perfect equilibrium when the fhell H is laid on the glafs plate C. Each of these parts, which are divided into quarters, indicates a grain. The lower divifions of the fcale will be found with more accuracy, if quarters of a grain be put in fucceffion, into the fhell H (after it has been laid on the plate C), and the ring s be moved between each quarter of a grain until the perfect equilibrium be restored. This place on the beam is then to be marked, and you may continue in this manner until the 30th part of a grain be given. Both fcales, for the fake of diftinctness, are only divided fo low as quarters of a grain; though the inftrument is fo delicate, and muft abfolutely be so, that 1-20th of a grain is fufficient to destroy the equilibrium.

The two glafs pillars M and N, together with the fteel forks affixed to them, are fo fitted into the stand, that both the beams lie parallel to each other as well as to the rod GE. In this pofition of the beams AB, the balls B and E are just in contact. The smallest glafs pillar N is of fuch a height that the ball of the beam CD ftands at the distance of exactly four lines from the ring G, and cannot move without touching the latter. The fmall fhell H is fufpended in fuch a manner that there is a distance of exactly two lines between it and the fhell C. In each of the brafs rings GG is a small hole, that the inftrument may be connected with the two fides of an electric jar. I is a brass wire, with a hollow bit of ivory, a, destined to fupport the beam CD, which is neceffarily preponderate at D, in order to prevent oscillation between the discharges to be examined by the inftrument.

It may be readily comprehended that, when the beam AB has moved, A muft pafs over twice the space that B does; and that in the beam CD, the cafe is the fame in regard to C and D. If AB be therefore connected with the external, and CD with the internal fide of a battery, but in such a manner that the inftrument is at a fufficient diftance beyond the electric atmosphere; and if the battery be charged, the repulfive effect of the electric power will oblige the ball B to feparate from the ball E; the fhell L must therefore naturally fink down with double velocity, fo that when the ball B rifes a line, the fhell H muft fink two when it reaches this depth it will touch the shell C, and the lat ter, by the power excited in it, will be obliged to fink, by which D muft naturally again afcend in a double proportion to the finking of C; fo that when C has fallen two lines, D must have afcended four, and D that moment touches the ring by which the two fides of the battery are connected with each other, and difcharges the battery.

But as the attractive electric power between unlike atmospheres, under like circumstances, is at least as ftrong as its repulfive power between like atmospheres, it would thence follow, that the electric power, inftead of repelling the ball B from the ball E, would rather attract D, and by its contact with G, promote the dif

2

ter.

charging; by which the inftrument would fail of its Electrome object, and be subjected to the temperature of the atmosphere like all other electrometers; and, befides this, the electric power could no longer be determined by weight. To obviate this inconvenience, the inftrument, in all electrical experiments, must be applied in fuch a manner that the power with which the ball D is attract ed by AB may exceed in ftrength the power required to repel the ball B from the ball E. For this purpose the rings must always be removed two divifions farther On CD, towards D, than the ring Q is shifted on AB towards B. If, for example, an electric force were required equal to eight grains, according to this electrometer, the ring Q must be removed to the place where 8 ftands, and the ring s to the place marked 10. The repulfive power will then naturally repel the balls B and E before G is in a condition to attract the ball D, as a power of two grains would be neceffary for this purpofe, befides that of the eight already in action. The fhell H with its weight of fourteen grains, will eafily overcome the preponderance of LD or LC, as it amounts only to ten grains, and therefore nothing exists that can impede the discharging.

When the ring 1, according to the required power, is removed fo far towards D, that the fhell H is not able by its weight to deftroy the preponderance of LD in regard to LC, the active power of the shell H muft be fo far increased by the addition of weights, that it can act with a preponderance of four grains on the plate C. If, for example, an electric power of 14 grains be required, the ring I must be removed to 16, by which LD refts upon a, with a preponderance of 16 grains in regard to LC. Now, to make H act on the plate C with a preponderance of four grains, it must be increased to 20 grains, that is, fix grains weight more must be added, as it weighs only 14; which fix grains are again laid upon LB; and therefore the ring Qis fhifted to 20, as the ftrength of the repulfive power is pointed out by 14 grains.

If an electric power of 25 grains be required, the rings must be removed to 27, and the weight of 17 grains be put into the hell H, in order to produce a preponderance of four grains in regard to s. These 17 grains are added to the required power of 25 grains, and the ring is pushed to 42, &c. In this manner the repulfive power always acts before the attractive power can.

It may be readily perceived that the faults and inconveniences common to all the electrometers hitherto employed, and which have been already mentioned, cannot take place here; because the discharging is performed by immediate connection between the pofitive and negative electricity in the inftrument itself, without any external means being employed.

One of the most effential advantages of this inftrument is, the certainty with which the fame refult may be expected when the experiment is repeated. From the fame degree of electric power, whatever be the temperature of the atmosphere, it will always be neceffary to commence the feparation of the two balls B and E from each other, the quantity of coated glass and the diftance of the ring Q from the axis L being the fame.

Another no lefs important advantage of this inftrument is, that in an experiment where the same electric power,

ter.

Electrome- power, often repeated, is neceffary to afcertain the refult with accuracy; fuch, for example, as the charging a battery through acids, water, &c.; the fame degree of precaution is not neceffary as is indifpenfably fo in any other electrometer, as the perfon who puts the machine in motion has nothing to do but to count how often the electrometer discharges itself; and the inftrument may be inclosed in a glass case, or prevented in any other manner from external contact, or any other circumstances which might render the experiment uncertain.

Pbil.

Magaz vol. iv.

Fig. 11.

Fig. 12.

Fig. 13.

"I flatter myself (fays M. Hauch), that the fimplicity of the conftruction of this inftrument, the facility with which it may be made at a very small expence, and the certainty that two inftruments, prepared according to the fame scale, with a like quantity of coated glass, muft exactly correspond with each other; but above all, that the certainty and accuracy by which experiments may be made with it, and by these means be accurately described, are advantages which will not be found united in any of the electrometers hitherto invented."*

We shall close this account of electrometers with defcribing the conftruction and ufe of M. Coulomb's electrometer, or, as he calls it, Electrical Balance.

ABDC (fig. 11.) represents a glass cylinder, twelve inches in diameter and the fame in height, covered by a glafs plate fitted to it by a projecting fillet on the under furface. This cover is pierced with two round holes one inch and three-fourths in diameter. One of them f is in the centre, and receives the lower end of the glafs tube fh, of twenty-four inches height, which is fixed in the hole with a cement made of fealing-wax, or other electric fubftance. The top of this tube receives the brafs collar H, (fig. 12. N° 3.) bored truly cylindrical with a fmall fhoulder, which refts on the top of the tube. This collar is faftened with cement, and receives the hollow cylinder (fig. 12. N° 2.), to which is joined the circular plate a b, divided on the edge into 360 degrees. It is alfo pierced with a round hole G in the centre, which receives the cylindrical pin i (fig. 12. N° 1.) having a milled head b, and furnished with an index io, whofe point is bent down fo as to mark the divifions on the circle a b. This pin turns stiffly in the hole G, and the cylinder moves fteadily in the collar H. To the lower end of the centre pin is fastened a little pincer, q, formed like the end of a port-crayon, and tightened by the ring 9, fo as to hold faft the fufpenfion wire, the lower end of which is grafped by a fimilar pincer, Po (fig. 13.) tightened by the ring 9. The lower end o is cylindrical, and is of fuch a weight, as to draw the wire perfectly ftraight, but without any risk of breaking it. It may be made equal to half of the weight that will juft break it.

This pincer is enlarged at C, and pierced with a hole, which tightly receives the arm g C q of the electrometer. This arm is eight inches long; and confists of a dry filk thread, or a lender ftraw completely dried, and dipped in melted lac or fine fealing-wax, and held perpendicularly before a clear fire, till it become a flender cylinder of about one-tenth of an inch in diameter. This occupies fix of the eight inches, from g to 9: the remaining two inches confift of a fine thread of the lac or fealing-wax, as it drains off in forming the arm. At a, is a ball of pith or fine cork,

ter.

one-fourth or one-half of an inch in diameter, made very Electromefmooth, and gilded. It is balanced by a vertical circle of paper g, of large dimenfions, made stiff with varnish. The refiftance of the air to this plane foon checks the ofcillations of the arm.

The whole inftrument is seen in its place in fig. IL. where the arm hangs horizontally about the middle of the height of the great cylinder. In its ofcillations the ball a moves round in a circle, whofe centre is in the axis of the whole inftrument. Its fituation is indicated by a graduated circle ≈ 0q, drawn on a flip of paper, and made to adhere to the glafs by varnish. The electrified body whofe action is to be obferved, is another small ball of cork t, alfo gilt, or a brafs ball well polished. This is carried by a stalk of lac mo, inclofing a dry filk thread. This ftalk is grafped by a clamp of cleft deal, or any fimilar contrivance, which is made to lie firm on the glafs cover. When this ball is let down through the hole m, it stands fo as to touch the ball a on the arm, when that ball is oppofite to o on the graduated circle.

In order to electrify the ball, we are to employ the infulating handle, fig. 14. which is a flender ftick Fig. 140of fealing-wax or lac, holding a metal wire that carries a fmall polished metallic ball. This is to be touched with some electrified body, fuch as the prime conductor of a machine, the knob of a jar, &c. This electrified ball is to be introduced cautiously into the hole m, and the ball t is to be touched with it. The ball a is immediately repelled to a distance, twisting the fufpenfion wire, till the force of twift exerted by the wire balances the mutual repulfion of the balls and a.

C

This is the procefs for examining the law of electric action. When it is defired to examine the action of different bodies in different ftates, another apparatus is wanted. This is reprefented by the piece c Ad (fig. 15.) confifting of a plug of fealing-wax A, fitting Fig. 15. tightly into the hole m, and pierced by the wire cd, hooked at c, to receive a wire to connect it occafionally with an electrified body, and having below a polished metal ball d.

The inftrument is fitted for obfervation in the following manner: The milled button b is turned at top, till the twift index io is at the mark o of the twift circle. Then the whole is turned in the collar H, till the ball a ftand oppofite to the mark o of the paper circle zo Q, and at the fame time the ball or d is touched. The obfervation is thus made. The ball is first electrified, as juft defcribed, and thus a is repelled, and retiring twifts the wire, fettling, after a few ofcillations, at fuch a distance as is proportional to the repulfion. The twiftindex is now turned fo as to force a nearer to t. The repulfion thus produced is estimated by adding the motion of the index to the angle at which the ball first ftopped. Giving the index another turn, we have another repulfion, which is estimated in a fimilar way, and thus we obtain as many measures as required.

It is not neceffary to make this inftrument of very large dimenfions; one 14 inches high, and five in diameter, of which the arm ag fhould occupy two inches and a half, will be, fufficiently large for moft purposes. The diameter of the glafs cylinder must always be double the length of the arm ag, that the pofition of this may not be disturbed by the action of the glass.

Dr Robifon confidered this electrometer as one of the

Electrome- the most valuable instruments that have been made, as ter. it is not only extremely delicate, but gives abfolute meafures with the greatest accuracy. For all purposes in which only repulfions were to be measured, he preferred it to his own inftrument described in ELECTRICITY, N° 206.

He, however, fuggefted feveral improvements in it, which are deferving of attention.

The bottom fhould be furnished with a round hole, admitting the lower end of the cylinder Cc belonging to the lower pincer (when the wire is ftrained at both ends) to hang freely, by which means much tedious ofcillation will be prevented. It is much more convenient to have the fufpenfion wire ftrained at both ends; and it should extend as far below the arm as above it, and the lower extremity fhould be grafped by a pincer that turns by a milled head in a hole at the end of a flender fpring. The inftrument may then be speedily adjusted by placing the twift index at o, and gently turning the lower button till the ball a point exactly at o on the paper circle.

The inftrument will be greatly improved, if, is place of the apparatus with the ball, we fubftitute the piece reprefented at fig. 15. making fome little changes in its construction. Thus, inftead of the wire cd, is ufed the smallest glafs tube that will admit of being varnished on the infide, which is done by drawing through it a filk thread dipped in varnish, made of lac.

The outside of the tube muft alfo be varnished, and a brass ball d fixed at its lower end, and a slender wire furmounted by a ball, is to be inferted into the tube, fo as to touch the ball below. The pofition of the ball d will not be liable to alteration, when the hole m is once ftopped with the plug. In making delicate experiments, the upper balle must be touched with the charger, reprefented at fig. 14. by which means the ball d is electrified. Then drawing out C by means of the forceps, the ball d is left completely infulated. In examining the electricity of the atmosphere, to which purpose this inftrument is well adapted, the wire must be allowed to remain in the tube.

It was by means of this incomparable inftrument, that M. Coulomb made the valuable experiments, to which we alluded in the article ELECTRICITY, when treating of the law of action of the electric fluid. By means of this electrometer, he alfo made his experiments on the diffipation of electricity into the air, and along imperfect conductors. He afcertained the law of diffipation into the air from bodies in contact, and the relation which this bore to the original repulfion, by first obferving the gradual approach of the ball a towards, in proportion as the electricity diffipated from both, and then flackening the twift index till the ball a refumed its original fituation.

The following was the general result of Mr Coulomb's experiments.

That the momentary diffipation of moderate degrees of electricity is proportional to the degree of electricity at the moment. He found that the diffipation is not fenfibly affected by the state of the barometer or thermometer; nor is there any fenfible difference of bodies of different fizes or different fubftances, or even different figures, provided that the electricity is very weak. But he found that the diffipation was greatly affected

ter.

by the different ftates of humidity of the air. In the Electromefcale of Sauffure's hygrometer, the relation to the quantity of water which a cubic foot of air is capable of holding in folution is diftinctly marked; the relation of this folution to the diffipation of electricity in Coulomb's experiments may hence be feen in the following table, the first column of which marks the degrees of Sauffure's hygrometer, the fecond how many grains of water are diffolved in a cubic foot of air at each degree, and the third column fhews the corresponding diffipation per minute. 69

6,197

The immediate object that M. Coulomb had in view in his experiments, was to afcertain the diminution of repulfion. He found that this, in a given ftate of the air, was a certain proportion of the whole repulfion taken at the moment of diminution, which is double the proportion of the denfity of the fluid; for the repulfions by which we judge of the diffipation are reciprocal, being exerted by every particle of fluid in the ball of the electrometer, on every particle of fluid in the ball a. The diminution of repulfion is therefore proportional to the denfity of the electric fluid in each ball; and, as during the whole diffipation, the denfities continue to have their original proportion, and as the diminution of repulfion is directly proportional to the diminution of the products of the denfities, it is confequently directly proportional to the fquare of either. If we put d for the denfity, the mutual repulfion will be reprefented by d3, and its momentary diminution by the fluxion of d3, or 2 d d= 2 dxd. But 2 dxd : d2 = 2 d : d. The diminution of repulfion obferved by experiment will be to the whole repulfion, in double the proportion that the diminution of denfity, or the diffipation of fluid will have to the whole quantity of fluid at the moment of obfervation. Let us, for instance, fuppofe the obferved diminution of repulfion to be; we may conclude, that the quantity of fluid loft by diffipation is M. Coulomb did not examine the proportion of the diffipations from bodies of various fizes. But we know, that if two fpheres communicate by a very long canal, their fuperficial denfities, and the tendencies of fluid to efcape from them, are inverfely as the diameters of the fpheres. Now, in a body that has twice the diameter of another body, the furface of the former is quadruple of that of the latter; and though the tendency of fluid to escape from the former is only the half of its tendency to ef cape from the latter, yet the greater furface of the former may fo far make up for its fmaller denfity, that

the