Pole, Analogous.
The end of a crystal of a pyroelectric substance, such as tourmaline,
which end when heated become positively electrified. On reduction of
temperature the reverse effect obtains.
Pole, Antilogous.
The end of a crystal of a pyroelectric substance, such as tourmaline,
which end, while increasing in temperature, becomes negatively
electrified. During reduction of its temperature the reverse effect
obtains.
Pole Changer.
(a) An automatic oscillating or vibrating switch or contact-breaker
which in each movement reverses the direction of a current from a
battery or other source of current of fixed direction, as such current
goes through a conductor.
(b) A switch moved by hand which for each movement effects the above
result.
Pole, Negative.
(a) In a magnet the south pole; the pole into which the lines of force
are assumed to enter from the air or outer circuit.
(b) In a current generator the pole or terminal into which the current
is assumed to flow from the external circuit. It is the negatively
charged terminal and in the ordinary voltaic battery is the terminal
connected to the zinc or positive plate.
Pole Pieces.
The terminations of the cores of field or other electro-magnets, or of
permanent magnets. These terminations are variously shaped, sometimes
being quite large compared to the core proper of the magnet.
They are calculated so as to produce a proper distribution of and
direction of the lines of force from pole to pole. As a general rule the
active field should be of uniform strength and the pole pieces may be of
contour calculated to attain this end.
Pole, Positive.
(a) In a magnet the north pole; the pole from which lines of force are
assumed to emerge into the air.
(b) In a current generator the pole or terminal whence the current is
assumed to issue into the outer circuit. It is the positively charged
terminal, and in the ordinary voltaic battery is the terminal connected
to the copper or carbon plate, termed the negative plate.
Poles.
(a) The terminals of an open electric circuit, at which there
necessarily exists a potential difference, produced by the generator or
source of electro-motive force in the circuit.
(b) The terminals of an open magnetic circuit; the ends of a magnetized
mass of steel, iron or other paramagnetic substance.
(c) The ends in general of any body or mass which show electric or
magnetic properties more developed than those of the central sections of
the body.