41C 
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E'LECTRICIT y. 
the diftance of exactly four lines from the ring G, and 
cannot move without touching the latter. The fmall 
fhell K is fufpended in fuch a manner that there is a dif¬ 
tance of.exaCt!y two lines between it and the (bell C. In 
each of tlie brafs rings G G is a fmall hole, that the in¬ 
ftrument may be connected with the two fides of an.elec¬ 
tric jar. I is a brafs wire, with a hollow bit of ivory a 
deflined to fupport the beam CD, which is nece'ftariiy 
preponderant at 'D, in order to prevent ofcillation between 
the difcharges to be examined by the inftrument. 
It may be readily comprehended that, when the beam 
A B has moved, A nuift pafs over twice the fpace that B 
does ; and that, in the beam C D, the cafe is the fame 
in regard to C and D. If A B therefore be connected 
with the external tide, aiid C D with the interna! fide,-of 
a battery, but in fftch a manner that the inftrument is at 
a fufficient diftance beyond the eleCtric atmofphere; and 
it the battery be charged, the repulfive effect of the elec¬ 
tric power will oblige the bail B to fe pa rate from the ball 
E ; the (hell H mult 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 fhell C, and the latter, by the power excited 
in it, will be obliged to fink, by which D muff naturally 
again afcend in a double proportion to the finking of C ; 
fo that when C has fallen two lines, D muft have afcend- 
ed four, and D that moment touches the ring by which 
the two tides of the battery are connected with eacli other, 
and difcharges the battery. 
But, as the attractive eleCtric power between unlike 
atmofpheres, under like circumftances, is at letiftas ftrong 
as its repulfive power between like atmofpheres, it would 
thence follow that the eleCtric power, inftead of repel¬ 
ling the ball B horn the ball E would rather attraCt D, 
and, by its contact with G, promote the difcharging ; by 
which the inftrument would fail of its object, and be fub- 
jeCted to the temperature of the atmofphere ; and befides 
this, the electric power could no longer be determined by 
weight. To obviate this inconvenience, the inftrument, 
in all electrical experiments, muft be applied in fuch a 
manner that the power with which the ball D is attracted 
by A B may exceed in ftrength the power required to re¬ 
pel the ball B from the ball E. For this purpofe the 
ring S muft always be removed two divifions farther on 
C D towards D, than tlie ring Q_is (hifted on A B to¬ 
wards B. If, for example, an eleCtric force were re¬ 
quired equal to eight grains, according to this electrome¬ 
ter, the ring Q^muft be removed to the place where 8 
ftands, and the ring S to the place marked io. Tlie re¬ 
pulfive 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 L D over L C, as it amounts only 
to ten grains, and therefore nothing ex ills that can impede 
the difcharging. 
When the ring S, according to the required power, is 
removed fo far towards D that the fhell If is not able by 
its weight to deftroy the preponderance of LD in regard 
to L C, the aCtive pow er of the fhell H muft be fo far in- 
creafed by the addition of weights, that it can aCt with a 
preponderance of four grains, on the plate C. If, forex- 
ample, an eleCtric power of.fourteen grains be required, 
the ring S muft be removed to 16, by which LD refts 
upon a , with a preponderance of fixteen grains in regard 
to LC. Now to make H aCt on the plate C with a pre¬ 
ponderance of four grains, it muft be increaled to twenty 
grains, that is, fix grains weight more muft be added, as 
it weighs only fourteen ; which fix grains are again laid 
upon L B ; and therefore the ring Q_js (hifted to 20, as 
the ftrength of the repulfive power is pointed out by 
fourteen grains. If an eleCtric power of twenty-five 
grains be required, the ring S muft be removed to 27, 
aiid the weight of feventeen grains be put into the fhell H 
in order to produce a preponderance of four grains in re¬ 
gard to S. The’fe fevenfeen grains are added to the re¬ 
quired power of twenty-five grains, and the ring Q^is 
puftreti to 42, &c. In this manner the repulfive power al¬ 
ways acts before the attractive power can begin to operate. 
It may be readily perceived that the faults and incon¬ 
veniences common to rnoft electrometers hitherto em¬ 
ployed, cannot take place here ; becaufe the difcharging 
is performed by immediate connection between the pofi- 
tive and negative eleCtricity in the inftrument itfelf, with¬ 
out any external means being employed. One of the 
mod effential advantages of this inftrument is, the cer¬ 
tainty with which the fame refillt may be expeCted when 
the experiment is repeated. For the fame degree of 
eleCtric power, whatever be the temperature of the at- 
mofphere, will always be neceffary to commence the re¬ 
paration of the two balls B and E from each other, the 
quantity of coated glafs and the diftance of the ring 
from the axis L being the fame. Another no lefs im¬ 
portant advantage of this inftrument is, that in an expe¬ 
riment where the fame eleCtric power, often repeated, is 
neceffary to afeertain the refult with accuracy ; fuch, for 
cxample, as the charging a battery through acids, water, 
&c. ; the fame degree of precaution is not neceffary as is 
indifpenfibly fo in the common electrometers, as the per- 
fon who puts the machine in motion has nothing to do 
but to count how often the electrometer difcharges it- 
felf; and the inftrument may be inclofed in a glafs cafe* 
or prevented in any other manner from external contaCt, 
or any other circtimftances which might render the expe¬ 
riment uncertain. 
Another more recent difcharging cleblrometer has been 
invented by Henry Lavvfon, efq. We flia 11 give the de- 
feription of it in his own words : “ Some time ago it 
(truck me that fome additions to Brookes’s electrometer 
might be made fo as to fit it for a good difcharging elec¬ 
trometer to meafure the repulfion between two balls (of 
a certain fize) in grains, and alfo effect the difeharge of a 
battery at the-fame time. The inftrument known by the 
name' of Cuthbertfon’s difcharging e/edlrojmtcr, was at that 
time the beft, and indeed the only inftrument for dil- 
charging batteries or jars by its own aCtion, then made ; 
but t think this will be found in the effentials, and in 
the theory and ufe, a more perfeCt inftrument. It is re- 
prefented in the EleCtricity Plate II. fig. 16. On the bafe 
S, is fixed the glafs pillar G, fupporting the hollow brafs 
ball B. T, is a light graduated brafs tube divided (from 
the weight W towards the ball B) into thirty parts, re- 
prefenting grains. W, is a Hiding weight. L, a light 
brafs ball ferewed to the end of the tube T, on the other 
end of which tube adjufts the heavy counter-balance-ball 
C, tlie tube T and its tvao balls being fufpended at their 
common center of gravity by a filk line in the center of 
the ball B, the mechanifm of which is fliewn in tlie plan 
or fection at the fide. The brafs ball F is ftationary, and 
of the fame fize as the ball L, and is fixed by a brafs arm 
to the ball B. The adjufting ball A is alfo of tlie fame, 
fize, and adjufts clofe to the ball L, or at any lower fta- 
tion between that and the ring r. The brafs 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 o line is marked, . 
on the faid tube at the ring r, when the three balls A L F 
are clofe together. The ring r ferves as an index, as tlie 
divifions pals in fuccellion into the glafs tube P, on lower¬ 
ing the ball A. Tlie hook H is ferewed into the bafe of 
P. The quadrant, or Henley’s eleCIrometer QJs (up- 
ported on a long brafs ftem to keep it out of the atmo¬ 
fphere of the lower part of the inftrument. The fide- 
plan or feclion fliews the internal conftruCtion of the ball 
B. In the firft place, the ball ferews in half, horizon¬ 
tally. The light tube T pa ties through the ball, and is 
fufpended nearly in the center of it by fome filk twift s, 
which fmall filk twift is fixed into the eye of the adjuft¬ 
ing wire a, part of which wire is filed fquare and goes 
through 
