The circuit for firing any single torpedo may thus be arranged; or, by moving the index to point toward “Battery on both” the circuits will be prepared for firing the two attached to that switch. By a proper manipulation of the switches the circuits may be prepared so that any one, two, or three, or all four of the torpedoes may be fired simultaneously. It must be borne in mind, however, that the electric switch is only a commutator for establishing the paths of the currents and that it must not be used as a firing-key. CHAPTER III. ELECTRICAL APPARATUS. FIRING-BATTERIES. Voltaic batteries are supplied for firing torpedoes from ships and boats. A modification of the Le Clanché cell has been adopted and is now issued from the Torpedo Station. One ship‘s firing-battery of six cells is supplied to such ships as are fitted with spars. For use in boats and elsewhere, as may be necessary, two boat‘s firing-batteries of four cells each, with two spare cells for each battery, are supplied. When the guns are to be fired by electricity an additional firing-battery will be furnished for the purpose. =_Note._=—Ships having only one torpedo launch will be supplied with but one boat‘s battery. THE CELL. =Plate XIII.= The positive element is zinc in the shape of a cylinder open at both ends. Around the zinc is molded a covering of okonite, which forms the jar of the cell. A lug from the zinc cylinder projects up through the okonite covering and has soldered to it the brass negative terminal of the cell. The negative element is a thin plate of platinum enclosed in a cylindrical muslin bag filled with crushed carbon. The bottom of the bag is closed by a flat, circular piece of ebonite. The top of the bag is seized to a plug of ebonite, through which passes a platinum wire, soldered to the platinum plate and to the brass positive terminal in the top. The ebonite plug is scored to take a rubber cover, the outer edge of which fits in a groove cut around the inside of the okonite cylinder above the top of the zinc, preventing loss of the liquid by splashing, or by evaporation. A hole in the cover permits the entrance of air, which is necessary for the proper operation of the cell. A rubber ring around the lower end of the negative element prevents its contact with the zinc. The liquid is a nearly saturated solution of sal-ammoniac (ammonium chloride). This cell polarizes rapidly on a short-circuit, but recovers in a few hours if left on open circuit. FIRING-BATTERY FOR SHIPS. The ship‘s firing-battery consists of six cells inclosed in a box. The cells are joined up in series. The terminals are at one end of the box, on top, and are covered by a lid hinged to the cover of the box. FIRING-BATTERY FOR BOATS. This pattern is similar to the ship‘s battery, except that four cells only are inclosed in its box. BATTERY TESTER. =Plate XIV.=