Simple harmonic motion. Oscillation.
’Phone. An abbreviation for the word Telephone.
Phonograph. An apparatus for reproducing sound. It is vibratory and not electric in its action, except that the mechanism may be driven by electricity. It consists of a rotating cylinder of a waxlike material and a glass diaphragm carrying a needle-point that lightly touches the surface of the waxen cylinder. If the diaphragm is agitated the needle vibrates, making indentations in the surface of the wax. If the needle is set back and the cylinder rotated so as to carry the point over the indentations, the sound is given back through the vibration of the diaphragm.
Pickle. An acid solution used to cleanse metallic surfaces preparatory to electro-plating.
Pilot Wires. Wires brought from distant parts of electric light and power mains, and leading to voltmeters at a central station. Through their agency the potential energy of every part of the system may be measured.
Pith-balls. Balls made from the pith of light wood, such as elder. They are used in the construction of electroscopes and for other experiments in static electricity.
Plant. The apparatus for generating electric current, including engines, boilers, dynamos, mains, and subsidiary apparatus.
Plate, Condenser. In a static apparatus, the condenser having a flat piece of glass for a dielectric. It is mounted on an axle so that it may be revolved.
Plate, Ground. In a lightning-arrester, the plate connected to the earth or ground wire.
Plate, Negative. In a voltaic battery, the plate which is unattacked by the fluid. It is made of carbon, platinum, or copper.