Specific Gravity. The relative weight or density of a body as compared with a standard. Water is usually taken as a standard for solids and liquids, and air for gases.
Speed-counter. An instrument which records the number of revolutions a shaft makes in a given time.
Spent Acid. Acid which has become exhausted. In a battery the acid becomes spent from combination with zinc; it also loses its depolarizing power.
Spring-contact. A spring connected to one lead of an electric circuit. It is arranged to press against another spring or contact, which it opens or closes by the introduction of a plug or wedge.
Spring-jack. An arrangement of spring-arm conductors under which plugs with wires attached can be slipped to make a new connection or to cut out certain circuits.
Spurious Resistance. (See [Resistance, Spurious].)
Standard Candle. (See [Candle, Standard].)
Standard Resistance. (See [Resistance, Standard].)
Starting-box. A resistance or shunt box used for letting current pass gradually into motors, instead of throwing on the full current at once.
Static Electricity. Electricity generated by friction; frictional electricity, such as lightning; electricity of high electro-motive force and practically uncontrollable for commercial purposes.