_Telegraph Battery._--For the purposes of telegraphing between torpedo stations, &c., a form of Leclanché battery, known as No. 3 commercial pattern, is generally used. _Voltaic Batteries._--The following points in connection with the use of voltaic batteries, which are taken from Beechey's 'Electro Telegraphy,' should be carefully observed:-- 1.--Each cell of a battery should be carefully insulated. 2.--The floors and tables in the battery room should be kept scrupulously clean and dry, so as to prevent the least leakage or escape of the current. 3.--The plates of a battery should be clean. 4.--Porous cells should be examined, and cracked ones replaced. 5.--No sulphate of zinc or dirt should be allowed to collect at the lips of the cells. In the case of a Daniell battery-- 1.--The solutions should be inspected daily, and crystals of sulphate of copper added as required. 2.--The zinc plate must not touch the porous cell, or copper will be deposited on it (the zinc). 3.--The battery should be charged with sulphate of zinc from the first. 4.--The copper solution must be watched and prevented from rising over the edge of the porous jar, the tendency of such solutions being to mix with each other by an action termed _osmosis_. These being in addition to foregoing general directions for Voltaic batteries. _Defects in a Voltaic Battery on its Current becoming Deficient._--On the electric current of a Voltaic battery becoming deficient, the following defects should be looked for:-- 1.--Solutions exhausted; for instance, sulphate of copper in a Daniell's entirely or nearly gone, leaving a colourless solution. 2.--Terminals or connections between the cells corroded, so that instead of metallic contact there are oxides of almost insulating resistance intervening in the circuit. 3.--Cells empty, or nearly so. 4.--Filaments of deposited metals stretching from electrode (pole) to electrode (pole). Also intermittent currents are sometimes produced by loose wires or a broken electrode, which alternately makes and breaks contact when shaken. Inconstant currents are also sometimes produced when batteries are shaken. The motion shakes the gases off the electrodes, thus increasing temporarily the electro-motive force of the battery. _Firing Keys and Shutter Apparatus._--The following is a description of the various firing keys and shutter signalling apparatus, which is used in connection with a system of electrical submarine mines. By means of the former the firing or other batteries may be thrown into circuit at will, whilst by means of the latter the firing battery is thrown in circuit without the aid of an operator, and a signal at the same instant given, indicating that a certain mine of the system has been struck.