Fig. 174. FRANKLIN'S PLATE.
Franklin's Theory.
The single fluid theory, q. v., of electricity.
Frequency.
The number of double reversals or complete alternations per second in an
alternating current.
Synonym--Periodicity.
Frictional Electricity.
Electricity produced by friction of dissimilar substances. (See
Electrostatic Series.) The contact theory holds that friction plays only
a secondary rôle in this process; that it increases the thoroughness of
contact, and tends to dry the rubbing surfaces, but that the charges
induced are due to contact of dissimilar substances, not to friction of
one against the other.
Frictional Heating.
The heating of a conductor by the passage of a current; the Joule
effect, q. v.
Fringe.
The outlying edge of a magnetic field.
Frog, Galvani's Experiment With.
A classic experiment in electricity, leading to the discovery of current
or dynamic electricity. If a pair of legs of a recently killed frog are
prepared with the lumbar nerves exposed near the base of the spinal
column, and if a metallic conductor, one half-length zinc and the other
half-length copper, is held, one end between the lumbar nerves and the
spine, and the other end against one of the muscles of the thigh or
lower legs, the moment contact occurs and the circuit is completed
through the animal substance the muscles contract and the leg is
violently drawn upwards. Galvani, in 1786, first performed, by accident,
this famous experiment, it is said, with a scalpel with which he was
dissecting the animal. He gave his attention to the nerves and muscles.
Volta, more happily, gave his attention to the metals and invented the
voltaic battery, described by him in a letter to Sir Joseph Banks, dated
1800.
Frog, Rheoscopic.
If the nerve or living muscle of a frog is suddenly dropped upon another
living muscle so as to come in contact with its longitudinal and
transverse sections, the first muscle will contract on account of the
stimulation of its nerve due to the passage of a current derived from
the second muscle (Ganot). The experiment goes under the above title.