The batteries must be examined daily. The connections must be kept clean and free from salts and, to secure this, the liquid must not be allowed to come in contact with them. Corroded connections can be cleaned with emery cloth, or, if very badly corroded, they may be scraped with the back of a knife-blade. Boat‘s batteries must be habitually examined after use in boats and any liquid that may have splashed about them be carefully wiped off. It sometimes happens that, from long use and impoverishment of the liquid, crystals of zinc-ammonium-chloride form in the cell, attaching themselves to the muslin bag and to the zinc. Sometimes these crystals build across from the bag to the zinc and prevent the ready removal of the negative element. When this occurs no effort should be made to remove it by force, for such a proceeding is liable to brake the platinum wire, or tear the thin platinum plate. To remove the negative element, take off the rubber cover and pour out the liquid, which should not be used again. Fill the cell with warm water and allow it to stand, full of water, for several hours. The crystals are but slightly soluble, but prolonged soaking will detach them sufficiently to permit the removal of the negative element. When this can be done the crystals are to be carefully picked off the muslin and scraped off the zinc. If such crystals are found in a cell, at any time, they must at once be removed and the liquid renewed. These batteries require but little care, but this little they must have. Systematic attention to them will be well repaid by their good performance and their constant readiness for use. Before the firing-batteries are returned into store at the end of the cruise, or before transportation to distant points, the negative elements must be removed from the cells, thoroughly soaked in fresh water and dried. The jars must be washed out and drained and all metal parts wiped perfectly dry. HAND-FIRING KEY. =Pattern B.—Plate XV.= This consists of two pieces of hickory, shaped to fit the hand, and joined together at the smaller end. Each piece is fitted with a brass contact stud projecting from its inner face at a short distance from the larger end. The natural spring of the wood keeps the two parts separated and maintains, normally, a break between the studs. A hole, bored longitudinally in each part, permits the entrance of a leading-wire, the bared end of which is secured by a screw to the contact stud. A rubber cot is seized over the key to prevent the closing of the circuit by sea-water. A safety-pin, attached to the key by a laniard, is habitually kept between the two parts to prevent accidental closing. The hand-firing key, introduced in an electrical circuit, provides a break that can be closed at will. THE TESTING-MAGNETO. This is a small magneto-electric machine, sending alternating currents into the external circuit. The circuit from the magneto includes an electro-magnet with a vibrating armature.