F = ( V^2 * S ) / ( 8 * PI * d^2 ) (2)
or
V = d * SquareRoot( (8 * PI * F ) / S ) (3)
As F is expressed as a weight, and S and a as measures of area and
length, this gives a means of directly obtaining potential values in
absolute measure. (See Idiostatic Method--Heterostatic Method.)
Synonyms--Attracted Disc Electrometer--Weight Electrometer.
Fig. 152. SECTION OF BASE OF PORTABLE ELECTROMETER.
In some forms the movable disc is above the other, and supported at the
end of a balance beam. In others a spring support, arranged so as to
enable the attraction to be determined in weight units, is adopted. The
cuts, Figs. 152 and 154, show one of the latter type, the portable
electrometer. The disc portion is contained within a cylindrical vessel.
Fig. 153. DIAGRAM ILLUSTRATING THEORY OF ABSOLUTE ELECTROMETER.
Referring to Fig. 152 g is the stationary disc, charged through the
wire connection r; f is the movable disc, carried by a balance beam
poised at i on a horizontal and transverse stretched platinum wire,
acting as a torsional spring. The position of the end k of the balance
beam shows when the disc f is in the plane of the guard ring h h. The
end k is forked horizontally and a horizontal sighting wire or hair is
fastened across the opening of the fork. When the hair is midway between
two dots on a vertical scale the lever is in the sighted position, as it
is called, and the disc is in the plane of the guard ring.