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Electrome- wood, C, by which it is held in the hand; the other will be observed upon the ball of the jar, and another Electrome

end is closed by a brass cap, D; the distance between at the end of the point.
the extremities of the small tube and that of the large Let us now apply this electrometer to useful observa-
one is filled with red wax, B, B ; on the cap Dis tions,
screwed at pleasure, either a ring E, or a brass hook In order to connect the idea of a determinate quanti.
F. The ring is used for applying the instrument to the ty of fluid to each degree of the electrometer, it is necef-
ball of a conductor, and the hook when it is hung fary to compare these degrees with the known quanti-
to a ring : on the cap D is a brass ftem G, termi- ties. Suppose for instance we have a jar, the coating

nating by a knob. This stem is bended, and the of which is fix inches square ; electrify it till a spon-
• extremity of its knob must be directly beneath the line taneous discharge takes place, and remark, by means

with which the graduated scale of the small tube com- of Henley's electrometer, at what degree this discharge
mences.

is effected. Again, electrify the jar, till it is nearly fa-
Round the large tube is a brass-ring H, half of which turated, and measuring with this electrometer, observe,
extends to the length of twelve or fifteen lines in the that the luminous point appears for instance at two de-
form of a half tube P, applied against the sides of the grees; then say, that when the electrometer, applied
tube. This gutter ferves to mark the degrees, by flid. to an electrified body, marks two degrees, the body
ing along the graduated scale by means of a button be- contains fix inches square of electricity. Repeat this
neath I. On the ring H is fixed one of the small experiment with a plate of glass, the coating of which is
ele&rometers invented by Sauffure, K, K, which is fur- seven, eight, ten, or twelve square inches, and we may
mounted by a ftem V, on which stem is fixed at pleasure form a scale of proportion, which is of the greatest uti-
either a point L, or a ball M, of the same size as that lity in accurate experiments.
which terminates the stem G, opposite which it is " In endeavouring to ascertain some of these pro-
placed. The extremity of this point or ball must be positions, (says M. Cadet), I have made an observation
placed immediately over the extremity of the half tube which has convinced me of the utility of my electrome-
or scale P, and horizontally to the centre of the ball, ter in discovering the capacity of electric apparatus.
which terminates the stem G.

Having taken a jar from an electric battery, I electri. At the top of Saussure's electrometer is a small ringfied it, and measured it with a point which I passed N, which serves to connect it with the chain Z when along a string of filk; on observing the distance at which required.

the luminous point appeared, I joined this jar to another To explain the use of this inftrument by a single ex- of the fame size, and imagined that by doubling the periment, charge a Leyden jar, till the spontaneous quantity of matter, the measure I had taken would also overflowing announces it to be saturated. Then place be doubled ; on the contrary, however, the latter the ring E on the knob of this bottle, and cause the measure was not more than about one-third of the forelectrometer of Sauffure, armed with its point, to slide mer: I then added a third bottle ; and fill obtained towards it. Observe the degree at which the divergence nearly the same result; whence the following proposiof the thread stream commences, and at that inftant tion appears to be established; namely, that the extent fuppress the point, and adapt in its place the ball M. of the electric atmosphere is in an inverse ratio to the Continue to advance the ele&rometer of Saussure till quantity of Auid accumulated, Another observation the electric pressure of the atmosphere in the jar causes which I have several times made, on measuring the electhe threads to diverge ; again observe the degrees, re- tric atmosphere of a conductor, is, that the limits of this place the point L, and close the shutters of the room; atmosphere form an elliptic figure around the body, then continue to advance the electrometer till the lumi- nearly similar to that represented at fig. 7. nous point appears, which again affords new degrees. “ This doubtless arises from the electrified body Lastly, replace the ball M, and fix the chain Z to the suspended in a chamber, being nearer to the earth than small ring N; cause it to communicate with the exte. the ceiling ; but it would be a curious experiment to riof coating of the jar, and advance the electrometer till measure it at an equal distance from every attracting the explofion takes place. Then comparing the different body, in order to observe whether the fluid has not degrees, we may ascertain the comparative difference really a tendency to descend towards the earth, rather between the respective methods.

than in any other direction. It is my intention to reAs soon as these relative proportions have been once peat this experiment, as I consider it of great imporaccurately ascertained by attentive observations, one of tance to ascertain whether electricity gravitates towards those methods alone will be sufficient for measuring the the globe. intensity of electricity; and, in fact, if the body intend- “ From these first attempts, I conceive my

I

electromeed to be submitted to examination be little charged with ter would be well adapted for measuring the absolute the electric fluid, the diverging of the threads, by means capacity of Leyden jars, and also their capacity with of the point, will fix the limits of the electric atmo- regard to their fize, or to the quality of ihe glass of. sphere : if it be more, the pressure of the atmosphere on which they are constructed; for the latter, by its the ball M, which is fubstituted for the point, will in- greater or less density, absorbs a greater or less quantity dicate this quantity. In short, if the body be loaded of Auid." with a confiderable mass of electric matter, it will be IV. Lawson's ELECTROMETER. This is a simplified shown by the luminous point. If a Leyden jar, instead improvement on Brooke's steelyard electrometer, and of being positively, is negatively electrified, the point should have been described when that inftrument was indicates it at the same time that it measures the elec. mentioned, instead of Mr Adams's; but it did not octric atmosphere, for instead of a luminous point, a star

a ftar cur to us till after that sheet was printed,

a

Fig. 7

a

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ter.

Fig. 8.

Electromé. The following account is given of this electrometer, is made : this being done, connect the battery or jar Electrome

, ter. in a letter from Mr Lawson to the editor of the Philofo- with the ball B, by means of the wire y, the end of phical Magazine.

which goes into B at the hole X, and should ftand at “ Some time ago it struck me that some additions to right angles to B, the ball of y resting on the battery : Brooke's electrometer might be made, so as to fit it for then connect the outside of the battery or jar with the a good discharging electrometer to measure the repulsion hook H.

hook H. As the battery charges, the electrometer Q
between two balls (of a certain fize) in grains, and also continues to rise ; and when it is so highly charged that

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effect the discharge of a battery at the same time. The the repulsive power between the balls L and Fis equal
instrument known by the name of Cuthbertson's dif- to the number of grains at which the weight W was
charging electrometer, (See ELECTRICITY, N° 203.) placed, the ball L will defcend, and deliver the charge
was at that time the best, and indeed the only in- of the battery to the ball A. The substance or thing
Arument for discharging batteries or jars by its own through which the shock is intended to be passed, must
action, then made ; but I think this will be found, in form part of the communication between the hook H
the essentials, and in the theory and use, a more perfect and the outside of the battery or jar."
inftrument.

V. Hauch's ELECTROMETER. Fig. 10. contains a re. Fig. 10.
“On the bafis (fig. 8.) is fixed the glass pillar G, presentation of this electrometer, and the different parts
supporting the hollow brass ball B. I is a light gra- of which it confifts. OP is a board of dry mahogany,
duated brass tube, divided (from the weigbt W towards twelve inches in length and four in breadth, which
the ball B) into 30 parts, representing grains. W serves as a stand for the instrument. In this board are
is a sliding weight. L, a light brass ball screwed to fastened two masly glafs pillars, M and N, which support
the end of the tube I. On the other end of which tube the two brass caps or rings GG, with the two forks of
adjusts the heavy counterbalance ball C, the tube I tempered steel KK screwed into them. The two rings
and its two balls being suspended at their common centre GG are well covered with varnish,
of gravity by a filk line in the centre of the ball B, the In the ring is faftened a brass rod, which terminates
mechanism of which is shewn in fig. 9. The brass ball in a ball E of the fame metal, and an inch in diameter.
F is stationary, and of the same fize as the ball L; and The length of the rod and ball together is four inches
is fixed by, and adjusts close to, the, ball L, or at any and a half.
lower station between that and the ringr. The brass A very delicate beam AB, the arms of which are of
tube to which the ball A is fixed is divided into inches, unequal length, moves on a short triangular axis (a knife

,
halves, and quarters : (a more minute division is unne- edge) of well tempered steel, on the fork K of the pillar
ceffary and improper). The divisions begin, or the line M. It is feventeen inches in length, and so constructed
o is marked on the said tube at the ring r, when the that the short arm forms a third, and the long one two-
three balls A, L, F, are close together. The ring thirds of the whole beam. The short arm of brass fur.
re serves as an index, as the divisions pass in succession nished with the ball B, exactly of the same fize as the
into the glass tube P on lowering the ball A. The ball E, is divided into forty-five parts equivalent to grains.
hook H is screwed into the base of P. The quadrant, The long arm A is of glass covered with copal varnish, ,
or Henley's electrometer, Q, is supported in a long brass and ends in an ivory ball A, into which is fitted an ivory

stem, to keep it out of the atmosphere of the lower part hook R, destined to support the ivory scale H. In order Fig. 9. of the inftrument. Fig. 9. shows the internal construc- to render the insulation more complete, this scale is suf

tion of the ball B, fig. 8. In the first place the ball pended by three hairs.
fcrews in half, horizontally. The light tube I pafles A very delicate beam CD, eleven inches in length,
through the ball, and is suspended nearly in the centre moves on an axis. like the former, on the pillar N,
of it by some filk twift, s, which small filk twift is fixed though not here fhewn. This beam is proportioned in
into the eye of the adjusting wire, a, part of which the same manner, one arm being a third and the other
wire is filed square and goes through the square hole h. two-thirds of the whole length. The long arm of brafs
The nut n screws on a, and serves to adjust the light is furnished at the end with a ball D, and divided into
tube I vertically. The light plates PP are of copper, thirty parts corresponding to grains. The short arm of

.
and move freely on the wire ww somewhat like a hinge, glass terminates in a long roundilh plate C, covered with
and rest on the copper wires CC, serving to make the copal varnish. The steel forks are shewn by the sections
direct communication between the inside and out of the of the two brass caps FF, as are also the two knife edges
battery or jar. NN are notches serving to let the tube L, L. By these caps the escape of the e:ectric matter
I defcend when the discharge is made. Into the tube Z is partly prevented.
the glass pillar is ground. Note, that at the bottom of A brass ring Q, capable of being moved along the
the notch N is a piece of brass filled with a Y, and short arm of the upper beam AB, Thews by means of
so placed as to keep the centres of the balls L and marks determined by trial and cut out on the beam,
F, fig. 8. under each other when they come close toge:

the number of grains which must be placed in the
ther.

small scale to restore the equilibrium of the beam,
“ When the instrument is adjusted, which is done by at each distance of the ring Q from the point of suf-
placing the weight W, fig. 8. at o on the line of grains, pension.
and then screwing or unscrewing the counterbalance On the long arm CD of the lower beam there is al-
ball C, till the tube I rises Dowly into its horizontal fo a moveable ring S, which, like the ring Q, shews in
pofition; then set the ball A at the distance from the grains, by its distance from the point of suspension, the
ball L that you choose, and the weight W placed at the power requifite to overcome the preponderance of LD
division or number of grains that you with the repulsive in regard to LC.
power of the electricity to arrive at before the discharge The power neceffary for this purpose will be found, if

the

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ter.

a

Hectrome- the shell H, which weighs exactly fourteen grains, be charging; by which the instrument would fail of its Electrome

suffered to link down on the glass plate C, and the ring object, and be subjected to the temperature of the at.
s be pushed forwards till both the arms of the beam are mosphere like all other electrometers; and, besides this,
in equilibrium. The part of the beam on which the the electric power could no longer be determined by
ring 's has moved, is divided into fourteen parts, so that weight. To obviate this inconvenience, the instrument,
o marks the place where the ring s must stand when in all electrical experiments, must be applied in such a
the beam, in its free state, is in equilibrium ; and 14 manner that the power with which the ball D is attracts
stands at the place where the ring s again restores a ed by AB may exceed in strength the power required
perfect equilibrium when the shell H is laid on the glass to repel the ball B from the ball E. For this purpose
plate C. Each of these parts, which are divided into the ring s must always be removed two divisions farther
quarters, indicates a grain. The lower divisions of the on CD, towards D, than the ring Q is shifted on AB
scale will be found with more accuracy, if quarters of a towards B. If, for example, an ele&tric force were re-
grain be put in succession, into the shell H (after it has quired equal to eight grains, according to this electro-
been laid on the plate C), and the ring s be moved be- meter, the ring Q must be removed to the place where
tween each quarter of a grain until the perfect equili. & ftands, and the ring s to the place marked 10. The
brium be restored. This place on the beam is then to repulsive power will then naturally repel the balls B and
be marked, and you may continue in this manner until E before G is in a condition to attra&t the ball D, as
the 30th part of a grain be given. Both scales, for the a power of two grains would be necessary for this

pur-
sake of diftinctness, are only divided so low as quarters pose, besides that of the eight already in action. The
of a grain ; though the instrument is so delicate, and shell H with its weight of fourteen grains, will easily
must absolutely be so, that 1-20th of a grain is sufficient overcome the preponderance of LD or LC, as it
to destroy the equilibrium.

amounts only to ten grains, and therefore nothing exists
The two glass pillars M and N, together with the that can impede the discharging.
steel forks affixed to them, are so fitted into the stand, When the ring 1, according to the required power,
that both the beams lie parallel to each other as well as is removed so far towards D, that the shell H is not
to the rod GE. In this position of the beams AB, the able by its weight to destroy the preponderance of LD
balls B and E are just in contact. The smallest glass in regard to LC, the active power of the shell H must
pillar N is of such a height that the ball of the beam be so far increased by the addition of weights, that it
CD ftands at the distance of exa&ly four lines from the can act with a preponderance of four grains on the
ring G, and cannot move without touching the latter. plate C. If, for example, an electric power of 14
The small shell H is suspended in such a manner that grains he required, the ring 1 must be removed to 16,
there is a distance of exactly two lines between it and by which LD refts upon a, with a preponderance of
the shell C. In each of the brass rings GG is a small 16 grains in regard to LC. Now, to make H act on
hole, that the instrument may be connected with the the plate C with a preponderance of four grains, it must
two sides of an electric jar. I is a brass wire, with a be increased to 20 grains, that is, fix grains weight
hollow bit of ivory, a, destined to support the beam more must be added, as it weighs only 14; which fix
CD, which is necessarily preponderate at D, in order grains are again laid upon LB; and therefore the ring
to prevent oscillation between the discharges to be ex- is thifted to 20, as the strength of the repulsive power
amined by the instrument.

is pointed out by 14 grains.
It may be readily comprehended that, when the If an electric power of 25 grains be required, the
beam AB bas moved, A must pass over twice the space rings must be removed to 27, and the weight of 17
that B does; and that in the beam CD, the case is the grains be put into the shell H, in order to produce a
fame in regard to Ċ and D. If AB be therefore con- preponderance of four grains in regard to s. These 17
nected with the external, and CD with the internal fide grains are added to the required power of 25 grains,
of a battery, but in such a manner that the instrument and the ring Q is pushed to 42, &c. In this manner
is at a sufficient distance beyond the electric atmosphere, the repullive power always acts before the attractive
and if the battery be charged, the repulsive effect of power can.
the electric power will oblige the ball B to separate It may be readily perceived that the faults and in-
from the ball E; the shell L must therefore naturally conveniences common to all the electrometers hitherto
fink down with double velocity, so that when the employed, and which have been already mentioned,
ball B rises a line, the shell H must fink two : when it cannot take place here ; because the discharging is per-
seaches this depth it will touch the shell C, and the lat. formed by immediate connection between the positive
ter, by the power excited in it, will be obliged to fink, and negative electrieity in the instrument itself, without
by which D must naturally again ascend in a double any external means being employed.
proportion to the finking of C; fo that when C has One of the most essential advantages of this inftru-
fallen two lines, D must have ascended four, and D ment is, the certainty with which the same result may
that moment touches the ring by which the two sides be expected when the experiment is repeated. From
of the battery are connected with each other, and dif. the same degree of electric power, whatever be the
charges the battery.

temperature of the atmosphere, it will always be necef-
But as the attractive ele&tric power between unlike fary to commence the feparation of the two balls B and
atmospheres, under like circumilances, is at least as E from each other, the quantity of coated glass and the
strong as its re pullive power between like atmospheres, distance of the ring Q from the axis L being the
it would thence follow, that the electric power, instead same.
of repelling the ball B from the ball E, would rather Another no less important advantage of this inftru-
attract D, and by its contact with G, promote the dif- ment is, that in an experiment where the same electric
2

power,

a

ter.

Electrome- power, often repeated, is necessary to ascertain the re- one-fourth or one-half of an inch in diameter, made very Electrometer. sult with accuracy ; such, for example, as the charging smooth, and gilded. It is balanced by a vertical circle

a battery through acids, water, &c.; the same degree of paper g, of large dimensions, made stiff with varnih.
of precaution is not necessary as is indispensably fo in The resistance of the air to this plane foon checks the
any other electrometer, as the person who puts the ma- oscillations of the arm.
chine in motion has nothing to do but to count how The whole instrument is seen in its place in fig. 11.
often the electrometer discharges itself; and the inftru. where the arm hangs horizontally about the middle of
ment may be inclosed in a glass case, or prevented in the height of the great cylinder. In its oscillations
any other manner from external contact, or any other the ball a moves round in a circle, whose centre is in
circumstances which might render the experiment un- the axis of the whole instrument. Its situation is indi.
certain.

cated by a graduated circle xog, drawn on a slip of
“ I Hatter myself (says M. Hauch), that the simplicity paper, and made to adhere to the glass by varnish.
of the construction of this instrument, the facility with The electrified body whose action is to be observed, is
which it may be made at a very small expence, and the another small ball of cork i, also gilt, or a brass ball
certainty that two instruments, prepared according to well polished. This is carried by a stalk of lac mo,
the same scale, with a like quantity of coated glass, must inclosing a dry filk thread. This stalk is grasped by a
exactly correspond with each other; but above all, that clamp of cleft deal, or any similar contrivance, which
the certainty and accuracy by which experiments may is made to lie firm on the glass cover. When this ball
be made with it, and by these means be accurately de- is let down through the bole m, it stands fo as to touch

scribed, are advantages which will not be found united the ball a on the arm, when that ball is opposite to o * Phil.

in any of the electrometers hitherto invented." * on the graduated circle. Magas. We shall close this account of electrometers with In order to electrify the ball t, we are to employ vol. iv.

describing the construction and use of M. Coulomb's the insulating handle, fig. 14. which is a slender ftick Fig. 146

electrometer, or, as he calls it, Electrical Balance. of fealing-wax or lac, holding a metal wire that carries Fig. 11. ABDC (fig. 11.) represents a glass cylinder, twelve a small polished metallic ball

. This is to be touched inches in diameter and the same in height, covered by a with some electrified body, such as the prime conductor glass plate fitted to it by a projecting fillet on the under of a machine, the knob of a jar, &c. This electrified surface. This cover is pierced with two round holes ball is to be introduced cautiously into the hole m, and one inch and three-fourths in diameter. One of them the ball t is to be touched with it. The ball a is imf is in the centre, and receives the lower end of the mediately repelled to a distance, twisting the suspension glass tube f h, of twenty-four inches height, which is wire, till the force of twist exerted by the wire bafixed in the hole with a cement made of sealing-wax, lances the mutual repulfion of the balls o‘and a.

or other electric substance. The top of this tube re- This is the process for examining the law of electric Fig. 12. ceives the brass collar H, (fig. 12. N° 3.) bored truly action. When it is desired to examine the action of

cylindrical with a small shoulder, which rests on the different bodies in different states, another apparatus is
top of the tube. This collar is faftened with cement, wanted. This is represented by the piece c Ad (fig.
and receives the hollow cylinder o (fig. 12. N° 2.), 15.) consisting of a plug of sealing-wax A, fitting Fig. 15.
to which is joined the circular plate a b, divided on the tightly into the hole m, and pierced by the wire cd,
edge into 360 degrees. It is also pierced with a round hooked at c, to receive a wire to connect it occasionally
hole G in the centre, which receives the cylindrical with an electrified body, and having below a polished
pin i (fig. 12. N° 1.) having a milled head b, and fur- metal ball d.
nished with an index i o, whose point is bent down so The instrument is fitted for observation in the follow-
as to mark the divisions on the circle a b. This pin ing manner : The milled button b is turned at top, till
turns stiffy in the hole G, and the cylinder o moves the twilt index io is at the mark o of the twist circle.
steadily in the collar H. To the lower end of the cen- Then the whole is turned in the collar H, till the ball
tre pin is fastened a little pincer, q, formed like the a land opposite to the mark o of the paper circle %0 Q,
end of a port-crayon, and tightened by the ring 9, so and at the same time the ball r or d is touched. The
as to hold fast the fufpenfion wire, the lower end of observation is thus made. The ball é is first electrified,
which is grasped by a fimilar pincer, Po (fig. 13.) as just described, and thus a is repelled, and retiring
tightened by the ring Q. The lower end oo is cylin- twists the wire, fettling, after a few oscillations, at such
drical, and is of such a weight, as to draw the wire a distance as is proportional to the repulfion. The twift-
perfectly straight, but without any risk of breaking it. index is now turned so as to force a nearer to t. The
It may be made equal to half of the weight that will repulfion thus produced is estimated by adding the mo-
just break it.

tion of the index to the angle at which the ball first
This pincer is enlarged at C, and pierced with a stopped. Giving the index another turn, we have another
hole, which tightly receives the arm g Cq of the elec- repulsion, which is estimated in a similar way, and thus
trometer. This arm is eight inches long; and confifts we obtain as many measures as required.
of a dry. filk thread, or a slender straw completely It is not necessary to make this inftrument of very
dried, and dipped in melted lac or fine sealing-wax, large dimensions; one 14 inches high, and five in dia-
and held perpendicularly before a clear fire, till it be- meter, of which the arm a g should

occupy two inches
come a slender cylinder of about one-tenth of an inch and a half, will be fufficiently large for most purposes.
in diameter. This occupies fix of the eight inches, The diameter of the glass cylinder must always be
from g to q: the remaining two inches consist of a fine double the length of the arm a g; that the position of
ibread of the lac or sealing-wax, as it drains off in this may not be disturbed by the action of the glass.
forming the arm. At q, is a ball of pith or fine cork, Dr Robison confidered this electrometer as one of

the

Fig. 13.

a

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ter.

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Electrome. the most valuable inftruments that have been made, as by the different ftates of humidity of the air. In the Electrome. ter. it is not only extremely delicate, but gives absolute scale of Saussure's hygrometer, the relation to the quan

measures with the greatest accuracy. For all purposes tity of water which a cubic foot of air is capable of
in which only repulfions were to be measured, he prefer. holding in folution is distinctly marked; the relation
red it to his own instrument described in ELECTRICITY, of this solution to the dissipation of electricity in Cou-
N° 206.

lomb's experiments may hence be seen in the following
He, however, suggested several improvements in it, table, the first column of which marks the degrees of
which are deserving of attention.

Saussure's hygrometer, the second how many grains of
The bottom should be furnilhed with a round hole, water are diffolved in a cubic foot of air at each degree,
admitting the lower end of the cylinder Cc belonging and the third column shews the corresponding diffipation
to the lower pincer (when the wire is strained at both per minute.
ends) to hang freely, by which means much tedious of.

69

6,197 cillation will be prevented. It is much more conveni- .

75

7,295 ent to have the suspension wire strained at both ends ;

8,045 and it should extend as far below the arm as above it,

87

9,221
and the lower extremity should be grasped by a pincer Hence it follows, that the dissipation is very nearly
that turns by a milled head in a hole at the end of a

in the triplicate ratio of the moisture of the air. Thus
slender spring. The instrument may then be speedily
adjusted by placing the twist index at o, and gently if we make is

7,197

; m will be= 2,764. If wo turning the lower button till the ball a point exactly at

6,180 o on the paper circle.

8,045 The initrument will be greatly improved, if, is place

make

6,180

; m will be = 2,76 ; and if we
of the apparatus with the ball t, we fubftitute the piece
represented at fig. 15. making some little changes in its

9,240

make .. = ; m will be = 3,61 ; or at a meconstruction. Thus, instead of the wire cd, is used

6,180
the smallest glass tube that will admit of being varnished

dium m will be = 3,40.
on the infide, which is done by drawing through it a The immediate object that M. Coulomb had in view
filk thread dipped in varnish, made of lac.

in his experiments, was to ascertain the diminution of
The outside of the tube must also be varnished, and repulfion. He found that this, in a given state of the
a brass ball d fixed at its lower end, and a slender wire air, was a certain proportion of the whole repulfion
surmounted by a ball, is to be inserted into the tube, taken at the moment of diminution, which is double
so as to touch the ball below. The position of the ball the proportion of the density of the fluid; for the re-
d will not be liable to alteration, when the hole m is pulsions by which we judge of the dissipation are reci-
once stopped with the plug. In making delicate ex. procal, being exerted by every particle of fluid in the
periments, the upper ball c must be touched with the ball i of the electrometer, on every particle of fluid in
charger, represented at fig. 14. by which means the ball the ball a. The diminution of repulfion is therefore
d is electrified. Then drawing out C by means of the proportional to the density of the electric Auid in each
forceps, the ball d is left completely insulated. In ex- ball; and, as during the whole dillipation, the denfities
amining the electricity of the atmosphere, to which continue to have their original proportion, and as the
purpose this inftrument is well adapted, the wire must diminution of repulfion is directly proportional to the
be allowed to remain in the tube.

diminution of the products of the densities, it is conIt was by means of this incomparable inftrument, fequently directly proportional to the square of that M. Coulomb made the valuable experiments, to either. If we put od for the density, the mutual which we alluded in the article ELECTRICITY, when repulsion will be represented by d®, and its momentreating of the law of action of the electric fluid. By tary diminution by the fluxion of d", or 2 d d=2 dxd. means of this electrometer, he also made his experi- But 2 dxd : d' = 2d:d. The diminution of repulments on the diflipation of electricity into the air, and fion observed by experiment will be to the whole realong imperfect conductors. He ascertained the law of pulfon, in double the proportion that the diminution of diffipation into the air from bodies in contact, and the denfity, or the diffipation of Auid will have to the relation which this bore to the original repulfion, by whole quantity of Auid at the moment of observation. first observing the gradual approach of the ball a to- Let us, for instance, suppose the observed diminution of wards i, in proportion as the electricity diffipated from repulfion to be as i we may conclude, that the quantiboth, and then slackening the twift index till the ball a ty of fluid loft by diffipation is g's. M. Coulomb did resumed its original situation.

not examine the proportion of the dissipations from boThe following was the general result of Mr Cou- dies of various fizes. But we know, that if two fpheres lomb's experiments.

communicate by a very long canal, their superficial That the momentary dissipation of moderate degrees densities, and the tendencies of fluid to escape from of ele&ricity is proportional to the degree of electricity them, are inversely as the diameters of the spheres. at the moment." He found that the dissipation is not Now, in a body that has twice the diameter of another sensibly affected by the state of the barometer or ther- body, the surface of the former is quadruple of that of mometer; nor is there any sensible difference of bodies the latter ; and though the tendency of Huid to escape of different sizes or different substances, or even differ. from the former is only the half of its tendency to efent figures, provided that the electricity is very weak. cape from the latter, yet the greater surface of the But he found that the dilipation was greatly affected former may fo far make up for its smaller density, that

the

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