This consists of a small wooden case inclosing a resistance-coil and a fuze-bridge. One end of the coil is connected to a brass spring and the other to one end of the fuze-bridge; the other end of the fuze-bridge is connected to a brass contact-piece opposite a spring at the other end of the case. When the tester is laid over the terminals of the battery and pressed down, contact is made between the contact-piece and spring, and a circuit established through the resistance-coil and bridge. If the battery is in good condition the bridge will be seen to redden, through a glass plate in the top of the case. The resistance of the coil in the tester for the ship‘s battery is 6.5 ohms and in the tester for the boat‘s battery it is 4 ohms. Should the fine wire bridge accidentally be broken, the plug must be removed and a new one inserted. A number of plugs, with bridges, are supplied for this purpose. MANAGEMENT AND CARE OF FIRING-BATTERIES. =To Prepare the Liquid.=—Make a saturated solution of sal-ammoniac with rain or distilled water. The solution will be hastened by crushing the crystals of sal-ammoniac and heating the water. Allow the solution to cool and settle, and decant it carefully. Then add one-tenth its volume of distilled or rain water. One pound of sal-ammoniac to four pints of water will give the proper degree of saturation. =To Fill the Cells.=—Press down the edge of the rubber cover at one point and, by inserting a screw-driver at this point, pry up the cover, and lift its edge all around. Introduce the liquid through a glass funnel, being careful to spill none of it on the connections, and fill the jars to within half an inch of the top. After twenty-four hours replenish the liquid, filling the jars to the same point as before, and replace the rubber cover. The ship‘s battery should be kept in a locker provided for it on the berth-deck, and should be kept connected with the wires leading to the firing apparatus on the spar-deck. Neither the ship‘s nor the boat‘s firing-batteries are to be tested too frequently, nor must the duration of a test be longer than is necessary. The batteries, if kept stationary in a proper locker, need be tested but once weekly. The boat‘s battery must be tested before it is sent into the boat, and again after it is put in place in the boat. The liquid should last from six to twelve months, according to the work done by the battery. Should the battery fail to show the proper test, search for bad or corroded connections. Test each cell separately, by touching the legs of a fuze-bridge directly to the poles of the cell. A single cell should redden the fuze-bridge when no other resistance is interposed. Faulty cells must be taken out, emptied and supplied with fresh liquid.