Encyclopaedia Britannica, or, a Dictionary of arts, sciences, and miscellaneous literature : enlarged and improved. Illustrated with nearly six hundred engravings > Volume 8, ELE-FOR

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Itkvftrome- the {hell H, which weighs exactly fourteen grains, be
, ter- fuffered to link down on the glafs plate C, and the ring
" " ,r be pulhed 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 itand when
the beam, in its free date, is in equilibrium ; and 14
Hands at the place where the ring s again reftores a
perfe£t equilibrium when the Ihell H is laid on the glafs
plate C. Each of thefe parts, which are divided into
quarters, indicates a grain. The lower divilions of the
leale will be found with more accuracy, if quarters of a
grain be put, in fucceffion, into the Ihell H (after it has
been laid on the plate C), and the ring s be moved be¬
tween each quarter of a grain until the perfect equili¬
brium be reftored. This place on the beam is then to
be marked, and you may continue in tins manner until
the 30th part of a grain be given. Both fcales, for the
fake of diftinclnefs, are divided only fo low as quarters
of a grain •, though the initrument is fo delicate, and
muft abfolutely be fo, that i-20th of a grain is fufftcient
to deftroy the equilibrium.
The two glafs pillars M and N, together with the
fteel forks ailixed to them, are fo fitted into the ftand
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 juft in contact. The fmalleft giafs
pillar N is of fuch a height that the ball of the beam
CD Hands at the diftance of exactly four lines from the
ring G, and cannot move without touching the latter.
The fmall fhell II is fufpended in fuch a manner that
there is a diftance of exactly two lines between it and
the ft>ell C. In each of the brafs rings GG is a fmall
hole, that the inftrument may be conne6ted with the
two fides of an eleftric jar. I is. a brafs wire, with a
hollow bit of ivory, a, deftined to fupport the beam
CD, which is neceffarily preponderate at D, in order
to prevent ofcillation between the difchargfes to be
examined by the inftrument.
It may be readily comprehended that, when the
beam AB has moved, A muft pafs over twice the fpace
that B does ; and that in the beam CD, the cafe is the
fame in regard to C and D. If AB be therefore con-
nefled with the external, and CD with the internal fide
of a battery, but in fuch a, manner that the inftrument
is at a fufficient diftance beyond the electric atmofphere;
and if the battery be charged, the repulfive effeft of
the eledlric power will oblige the ball B to feparate
from the ball E ; the Ihell L muft therefore naturally
fink down with double velocity, fo that when the
ball B rifes a line, the {hell H muft fink two : when it
reaches this depth it will touch the {hell 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 muft have afcended four, and D
that moment touches the ring by which the two fides
of the battery are connecled with each other, and dif-
charges the battery.
But as the attractive electric powTer between unlike
atmofpheres, under like circumftances, is at leaft as
ftrong as its repulfive power- between like atmofpheres,
it would thence follow, that the electric power, inftead
ef repelling the ball B from the ball E, would rather
attradt D, and by its contadt with G, promote the dif-
C
] E L E
charging j by which the inftrument would fail of its Eledtrome.
object, and be fubjedted to the temperature of the at - , ,
mofphere like ail other eledtrometers j and, befides this,
the eledtric 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 attract ¬
ed by AB may exceed in ftrength the power required
to repel the ball B from the baft E. For this purpofe
the ring r muft always be removed two divifions farther
on CD, towards D, than the ring ()_ is ftiiited on AB
towards B. If, for example, an eledtric force were re¬
quired equal to eight grains, according to tins electro¬
meter, the ring f) mult be removed to the place where
8 Hands, 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 attradl the ball D, as
a power of two grains would be neceffary for this pur¬
pofe, befides that of the eight already in action. The
ihell IT 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 exifts
that can impede the difeharging.
When the ring 1, according to the required power,
is removed fo tar towards D, that the {hell H is not
able by its weight to deftroy the preponderance of LD
in regard to LC, the adtive power of the {hell H muft
be fo far increafed by the addition of weights, that it
can act with a preponderance of four grains on the
plate C. If, for example, an eledlric power of 14
grains be required, the ring 1 muft be removed to 16,
by which LD refts upon a, with a preponderance of
16 grains in regard to LC. Now, to make H adt on
the plate C with a preponderance of four grains, it mull
be increafed to 20 grains, that is, ftx grains weight
more muft be added, as it weighs only 14 j which fix
grains are again laid upon LB j and therefore the ring
is fliifted to 20, as the ftrength of the repulfive power
is pointed out by 14 grains.
If an eledlric power of 25 grains be required, the
ring s muft 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 r. T hefe 17
grains are added to the required power of 25 grains,
and the ring is puftied to 42, &c. In this manner
the repulfive power always adds before the attradliye
power can.
It may be readily perceived that the faults and in¬
conveniences common to all the eledlrometers hitherto
employed, and which have been already mentioned,
cannot take place here ; becaufe the difeharging is per¬
formed by immediate connedtion between the pofitive
and negative eledlrieity in the inftrument itfelf, without
any external means being employed.
One of the moft effential advantages of this inftru¬
ment is, the certainty Avith Avhich the fame refult may
be expedled Avhen the experiment is repeated. From
the fame degree of eledlrie poAver, whatever be the
temperature of the atmofphere, it will always be necef¬
fary to commence tire feparation of the tAvo balls B and
E from each other, the quantity of coated glafs and the
diftance of the ring Q from the axis L being the
fame.
Another no lefs important advantage of this inftru¬
ment is, that in an experiment where the fame eledlric
poAver,.