If the prime conductor is connected to the earth and the cushions are
left insulated, negative electricity can be collected from the cushions.
In some machines both prime conductor and cushions are kept insulated
and without ground contact. Electrodes connecting with each are brought
with their ends close enough to maintain a sparking discharge.
Machine Influence.
A static electric machine working by induction to build up charges of
opposite nature on two separate prime conductors. In general they are
based on the principle of the electrophorous. Work is done by the
operator turning the handle. This rotates a disc and draws excited parts
of it away from their bound charges. This represents a resistance to
mechanical motion. The work absorbed in overcoming this mechanical
resistance appears as electric energy. There are various types of
influence machines, the Holtz, Toeppler-Holtz and Wimshurst being the
most used. The electrophorous, q. v., is a type of influence machine.
Machine, Holtz Influence.
A static electric machine. It includes two plates, one of which is
rapidly rotated in front of the other. Two armatures of paper are
secured to the back of the stationary plate at opposite ends of a
diameter. To start it one of these is charged with electricity. This
charge by induction acts through the two thicknesses of glass upon a
metal bar carrying combs, which lies in front of the further side of the
movable plate. The points opposite the armature repel electrified air,
which strikes the movable disc and charges it. A second rod with comb at
the opposite end of the same diameter acts in the reverse way. Thus
opposite sections of the disc are oppositely charged and the combs with
them. By induction these portions of the disc react upon the two
armatures. The opposite electricities escape from the armatures by paper
tongues which are attached thereto and press against the back of the
movable plate. As the plate rotates the opposite electricities on its
face neutralize the electricity repelled from the combs. The charges on
the back strengthen the charges of the armatures and brass combs. Thus
the machine builds up, and eventually a discharge of sparks takes place
from the poles of the brass combs.