=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. =Static Shock.= A term used in electro-therapeutics for describing the discharge from a small condenser or Leyden-jar; also the effect produced by the action of the vibrator of the induction-coil. =Station, Central.= The building or place in which the electrical apparatus is installed for the generation of current; the headquarters of telephone lines. =Steady Current.= An electric current whose strength is fixed or invariable. =Stock-ticker.= An instrument employed to give quotations of stocks by telegraphic record. A paper tape runs through an electrical machine which prints on it the figures and letters that stand for stocks and their values. The whole system is operated from a station located in the Stock-exchange. =Storage Accumulator.= (_See_ Accumulator, Storage.) =Storage-battery.= (_See_ Battery, Storage.) =Strength of Current.= Amperage; the quantity of current in a circuit. =Stripping.= The process of removing electro-plating, or thin metal coatings, from an object before it is re-electro-plated. =Stripping Liquid.= The liquid in a stripping-bath used for removing metals from surfaces before re-plating them. =Submarine Cable.= A telegraphic cable laid at the bottom of the sea or any body of water. =Submarine Search-light.= An incandescent light which works under water. =Sub-station.= A generating or converting plant subsidiary to a central station, and placed so as to supply current in a district situated at a distance from the main power-house. =Subway, Electric.= An underground passageway utilized for carrying cables and wires. =Sweating.= A process by which the ends of cables are brought together and soldered.