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

L E
Eic&romo- Dlftance of tlie
, in fourths of
2
3
4
5
6
7
8
9
10
11
12
* !3
14
15
16
J7
18
J9
20
21
22
23
24
E
balls
a line.
[
Correfponding forces
of electricity.
3
4
5
6
8
10
12
14
J7
20
23
26
29
32
36
40
44
48
52
56
60
64
Thofe who are defirous to carry this meafure of the
cleCtric force further, may do it by having limilar e-
leCtrometers conltructed, but made upon a larger fcale,
and with heavier balls, which would only feparate one
line, with the degree of electricity that makes the
1 mailer ones diverge fix lines • thefe would confequently
meafure a force 1024 times greater than that which
forms the unity of the preceding table ; and thus by
degrees we may be enabled to difeover the ratio of the
itrongeft difeharge of a great battery, or perhaps even
of thunder itfelf, to that of a piece of amber, which
only attracts a bit of draw or anyt other light fub-
ftance.
In order to obferve the electricity of the atmofphere
with this inftrument, we mult firil bring the electric
fluid contained in the electrometer to the fame degree
of denfity with that at the furface of the earth ; this is
eafily done by letting the bottom and top touch the
ground at the fame time ; then raife the point, keep¬
ing the bottom dill in contact with the ground, from
whence it may be lifted up in a vertical polition till the
balls are level with the eye.
i he fecond circumdance is to render the divergence
of the balls, which is occafloned by the electricity of
the air, permanent. This is effected by touching the
top of the cleftrometer with the finger 5 but here the
acquired eleftricity becomes contrary to that of the bo¬
dy by which they are eleftrified. Let us fuppofe, for
example, that the eleftrometer is at five feet from the
ground, and the balls diverging; touch the top of the
eleftrometer with the finger, and the balls will clofe ;
but they will again open, if the eleftrometer is with¬
drawn from the influence of the eleftricity of the air,
by being brought nearer the ground, or into the houfe.
M. Saufllire only employed this method when the elec¬
tricity was fo weak that he could not perceive any un¬
til the eleftrometer was raifed confiderably above his
•ye t as in this cafe he could not perceive the diver-
3 ] E L E
gence of the balls, he always endeavoured to obtain a Ele&rome-
permanent eleftricity in the foregoing manner. ter-
The following example will render the ufe of the v ~
foregoing obfervations more familiar. Choofe an open
fituation free from trees and houfes, ferew the conductor
on the top of the eleftrometer, lay hold of it by its
bafe, and place it fo that the bafe and conduftor may
touch the ground at the fame time; then elevate it to
the height of the eye, and obferve the quantity oflines,
or fourths of a line, that the balls have diverged ; now
lower it till the balls almoft touch each other, and ob¬
ferve at what diftance the top of the conduftor is from
the ground 5 and this is the height from the ground at
which the eleftricity of the air begins to be fenfible.
If the eleftricity of the air is fufficiently ftrong to make
the balls diverge when it Hands upon the ground, one
of the lengths of the eleftrometer mult be unferewed
from it. If the balls, however, Hill diverge, the other
parts of the conduftor ihould alfo be unferewed, and
you may mark down, that the eleftricity is fenfible at
zero, or on the furface of the earth. If, on the con¬
trary, the eleftricity is fo weak, as not to caufe the
balls to diverge when they are even with the eye, and
confequently when the conduftor is two feet higher, or
feven feet from the ground, you ihould then raife it a
foot higher; while it is thus elevated, touch the top
with the other hand ; when this hand is taken away,
lower the eleftrometer, and if it is eleftrified, you may
fay the eleftricity is fenfible at eight feet 5 if it is not,
raife it as high as the arm can reach, and repeat the
fame operation ; if any eleftricity is found, write down
eleftricity fenfible at nine feet 5 if not, mark o, or no
eleftricity relative to this inftrument, and this mode of
employing it 5 for figns of eleftricity may ftill be ob¬
tained, by throwing a metallic ball 50 or 60 feet into
the air, which is at the fame time connefted with the
eleftrometer by a metallic thread.
One advantage of this inftrument is, that it will often
exhibit figns of eleftricity when none can be obtained
from a conduftor of 100 feet in height, becaufe it can
more eafily be preferved from humidity, &c. which will
deftroy the inhalation of the large conduftors.
This eleftrometer may be ufed inftead of the con-
denfer of M. Volta, by only placing it on a piece of
oiled filk, fomewhat larger than the bafe of the inftru¬
ment; but in this cafe, it is the bafe, and not the
top of the inftrument, which muft be brought into
contaft with the fubftance whofe eleftricity is to be ex¬
plored.
It is eafy to difeover alfo by this inftrument, the elec¬
tricity of any fubftance, as of cloths, hair of different
animals, &c. For this purpofe, it muft be held by the
bafe, and the fubftance rubbed brilkly (only once) by
the ball of the eleftrometer ; the kind of eleftricity
may be afeertained in the ufual manner. It is proper,
however, to obferve here, that as the top of the eleftro¬
meter afts in this cafe as an infulated rubber, the elec*
tricity it acquires is always contrary to that of the rub¬
bed body.
III. Cadet's Electrometer, is thus deferibed by
the author, as tranflated in Nicholfon’s Journal.
Fig. 6. In a glafs tube A, 18 or 20 inches long, Fig. 6,
is inclofed another fhorter tube X, fealed at botli ends.
This tube contains a graduated fcale : one of the ends
of thefe two tubes is cemented in a handle of turned
A 2 wood,.