Contact-spring.
A spring connected to one lead of an electric circuit, arranged to press
against another spring, or contact point, q. v., under any conditions
determined by the construction of the apparatus. (See Bell,
Electric--Coil, Induction.)
Contact Theory.
A theory devised to explain electrification, the charging of bodies by
friction, or rubbing, and the production of current by the voltaic
battery. It holds that two bodies, by mere contact become oppositely
electrified. If such contact is increased in extent by rubbing together,
the intensity of their electrification is increased. This
electrification is accounted for by the assumption of different kinetic
energy, or energy of molecular motion, possessed by the two bodies;
there being a loss and gain of energy, on the two sides respectively,
the opposite electrifications are the result. Then when separated, the
two bodies come apart oppositely electrified.
The above accounts for the frictional production of electricity. In the
voltaic battery, a separation of the atoms of hydrogen and oxygen, and
their consolidation into molecules occurs, and to such separation and
the opposite electrification of the electrodes by the oxygen and
hydrogen, the current is attributed, because the hydrogen goes to one
electrode, and the oxygen to the other, each giving up or sharing its
own charge with the electrodes to which it goes. If zinc is touched to
copper, the zinc is positively and the copper negatively electrified. In
the separation of hydrogen and oxygen, the hydrogen is positively and
the oxygen negatively electrified. In the battery, the current is due to
the higher contact difference of oxygen and hydrogen compared to that
between zinc and copper. It will be seen that the two contact actions in
a battery work against each other, and that the current is due to a
differential contact action. The zinc in a battery is electrified
negatively because the negative electrification of the oxygen is greater
in amount than its own positive electrification due to contact with the
copper.
Contractures.
A muscular spasm or tetanus due to the passage of a current of
electricity; a term in electro-therapeutics.
Controlling Field.
The magnetic or electro-magnetic field, which is used in galvanometers
to control the magnetic needle, tending to restore it to a definite
position whenever it is turned therefrom. It may be the earth's field or
one artificially produced.
Controlling Force.
In galvanometers and similar instruments, the force used to bring the
needle or indicator back to zero. (See Controlling
Field--Electro-Magnetic Control--Gravity Control--Magnetic
Control--Spring Control.)