ELECTRICITY. 
Tit tie below die center of gravity, and equally balanced 
with a hollow brafs ball at each end, the center, or axis, 
reding upon a proper fliaped piece of brafs fixed in the 
infide of the ball c; that fide of the hemifphere towards 
c is cut open, to permit the end c A of the balance to de- 
feend till it touches the ball a, and the upper hemifphere 
C is alfo cut open to permit the end r B to afeend; i is a 
weight, weighing a certain number of grains, and made 
in the form of a pin with a broad head ; the ball B has 
two holes, one at the top, and the other at the bottom ; 
the upper hole is fo wide, as to let the head of the pin 
pafs through it, but to flop at the under one, with its 
fhank hanging freely in b ■, k is a common Henley’s qua¬ 
drant electrometer; and when in life it is ferewed upon 
the top of c. It is evident, from the conftrudlion, that if 
the foot ftanu horizontal, and the ball B be made to touch 
b, it will remain in that pofition without the help of the 
weight 2 ; and if it (hould by any means receive a very 
low charge of eledlric fluid, the two balls b, B, will repel 
each other; B will begin to afeend, and, on account of 
the center of gravity being above the center of motion, 
the afeenfion will continue till A reft upon a. If the ba¬ 
lance be fet again horizontal, and the pin i be put into its. 
place in B, it will caufe B to reft upon b, with a preflfure 
equal to that weight, .fo that more eledlric fluid mtift be 
communicated than formerly before the balls will fepa- 
rate ; and as the weight in B is increafed or diminiftied, 
a greater or lefs quantity of eledlric fluid will be required 
to effect a feparation. 
When this inftrument is to be applied to a jar, or bat¬ 
tery, one end of a wire L mult be inferted into a hole in 
6 , and the other end into a hole of any ball proceeding 
from the infide of a battery, or jar, as M. A chain, or 
wire, or any body through which the charge is to pafs, 
muft be hung to the hook at m, and carried from thence 
to the outfide of the battery, as is reprefented by the line 
N ; k muft be ferewed upon c, with its index towards A. 
The reafon of this inftrument being added, is to fliew, 
by the index continuing to rife, that the charge of 
the battery is increafing, becattfe the other part of the 
inftrument does not ~adt till the battery has received its 
required charge. It may be here obferved, that this in- 
flrument conlifts of three electrometers, viz. Henley’s 
eleClrometer, Lane’s difeharging electrometer confidera- 
bly improved, and Brookes’s fteelyard electrometer im¬ 
proved likewife. By this combination and thefe improve¬ 
ments, we poffefs all that can be required in an electro¬ 
meter for batteries and large jars; for, by k, we fee the 
progrefs of the charge; by the feparation of B£, we have 
the repulfive power in weight; and by the ball A, the 
difeharge is made whenever the charge has acquired the 
ftrength propofed. Example : Prepare the electrometer 
in the manner thewn in the figure, with the jar M an¬ 
nexed, which contains about 168 fquare inches of coating. 
Take out the pin in B, and obferve whether the ball B 
will remain at reft upon b ; if not, turn the adjufting ferew 
at C till it juft remains upon A. Put into B the pin, 
marked i, weighing 15 grains; take two inches of watch- 
pendulum wire, fix to each end a pair of fpring tongs, 
reprefented at G m, hook one end to m, and the other to 
the wire N, communicating with the outfide of the jar; 
let the prime condudlor of an eledlrical machine, or a 
wire proceeding from it, touch the wire L; then, if the 
machine be put in motion, the jar and eledlrometer will 
charge, as will be feen by the rifing of the index k ; and 
when charged high enough, B will be repelled by b, and 
A will defeend and difeharge the jar through the wire 
which was confined in the tongs, and the wire will be 
fufed and run into balls. The ingenious inventor, by 
breathing through a glafs'pipe into the jar, damped it a 
little in the infide. Then loading B with a pin of thirty 
grains, he obtained fucit a charge as fufed eight inches of 
watch-pendulum wire, difpofed exactly as the two inches 
were difpofed in the former experiment. And by repeat¬ 
ing and varying his experiments, he found that double 
41.5 
quantities of eledlrical fl 11 id, in the form of a difeharge, will 
melt four times the length of wire of a certain diameter. 
A very ingenious dijcharg-big balance electrometer has been 
lately invented by A. W. Von Haucll, of the royal fo- 
ciety of .Copenhagen ; which is reprefented in t he fame 
engraving, at fig. 15. OP is a board of dry mahogany, 
which ferves as a (land for the inftrument. In this board 
are faftened two glafs pillars, M and N, which fupport: 
the two brafs caps or rings GG, with the two forks of 
tempered fteel KK ferewed into them. Tire two rings 
GG are well covered with varnifh. In the ring G is 
fiftened a brafs 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 fliarp triangular gxis (a knife edge) 
of well tempered fteel on the fork K of the pillar M. 
It is feventeen inches in length, and fo conftrudfed that 
tlie Ihort arm forms a third, and the long one two-thirds, 
of the whole beam. The fhort arm of brafs furnifhed 
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 varnifh, 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 inhalation more complete, this fcale is fuf- 
pended by three hairs. A very delicate beam, C D, ele¬ 
ven inches in length, moves on an axis, like the former, 
on the pillar N. This beam is proportioned in the fame 
manner, one arm being a third and the other tivo-third 
of the whole length. The long arm of brafs is furnifhed 
at the end with a ball D, and divided into thirty parts 
correfponding to grains. The fhort arm of glafs termi¬ 
nates in a long roundifh plate C, covered with copal var¬ 
nifh . The fteel forks are fnewn by the fedtions of the 
two brafs caps F F, as are alfo the two knife edges L L. 
By thefe caps the efcape of the electric fluid is partly 
prevented. A brafs ring (^capable of being moved 
along the ihort arm of the upper beam A B, fliews, by 
means of marks determined by trial and cut out on the 
beam, the number of grains which in 11 ft be placed in the 
fmall fcale to reftoi'e the equilibrium ot the beam at each 
diftance of the ring Q^frorn the point of fitfpenfion. On 
the long arm C D of the lower beam there is alfo a move- 
able ring S, which, like the ring QJhews in grains, by 
its diftance from the point of fufpenfion, the power requi- 
fite to overcome the preponderance ot L D in regard to 
LC. The power neeefTary for this purpofe will be found 
if the fcale or (hell H, which weighs exadfiy fourteen 
grains, be fuffered to fink down on the glafs plate C, and 
"the ring S be puftied forwards till both the arms of the 
beam are in equilibrium. The part of the beam on which 
the ring S has moved is divided into fourteen parts, fo 
that o marks the place where the ring S muft (land when 
the beam, in its free ftate, is in equilibrium ; and 14 (lands 
at rite place where the ring S again reftores a perfect equi¬ 
librium when the (hell H is laid on the glafs plate C. 
Each of thefe parts, which are divided into, quarters, in¬ 
dicates a grain. The lower divifions of the fcale will be 
found with more accuracy if quarters of a grain be put, 
in fuccellion, into the (hell H (after it has been laid on 
the plate C), and the ring S be moved between each 
quarter of a grain until the perfedl equilibrium be re- 
ftored. This place o"n the beam is then to be marked, 
and traced in this manner, until the 30th part of a grain 
be given. Both feales, for the fake of diftindlnefs, are 
divided only fo low as quarters of a grain ; though the 
inftrument is fo delicate, and-muft abfolutely be fo, that 
i-aoth of a grain is flifficient to deftroy the equilibrium. 
The two glafs pillars M and N, together with the fteel 
forks affixed to them, are fo fitted into the ftand, that 
both the beams lie parallel to each other as well as to the 
rod G E. In this pofition of the beams A B, the balls B 
and E are juft in contadl. The fmalleft glafs pillar N is 
of fuch a height, that the ball of the beam C D Hands at 
i the. 
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