An electrophorus is an instrument, invented by Alessandro Volta,
for obtaining electricity by means of induction.
A tin mold, A (refer to diagram), kept in connection with the ground,
is filled with shellac or resin, B, and has a movable metal cover,
C, with a glass handle, D. When the surface of the shellac
or resin is rubbed with fur this produces a negative charge on the resin.
When the cover is brought near the lower part of the apparatus, it is charged
positively on its under surface, negatively on its upper. If then it is
touched, the negative charge escapes and the cover becomes positively charged;
and if removed and applied to any conductor, it will give a positive charge
to it. This may be repeated often but with a slight reduction of B's charge.
The earth connection may be made by a metallic pin passing through B
to A, or by a piece of tinfoil, e, pasted from the edge
of A over on to B.
Diagram from a 1908 encyclopedia