As platinum wire or low tension fuzes are now universally adopted as the mode of ignition for submarine mines, it will be only necessary to describe those electrical batteries which are most suitable as an exploding agent in connection with such fuzes; these are as follows:-- 1.--Siemens's dynamo low tension machine. 2.--Von Ebner's Voltaic battery. 3.--Chromic acid or Bichromate Voltaic battery. 4.--Leclanché's Voltaic battery. _Siemens's Low Tension Dynamo Electrical Machine._--This instrument consists of an electro magnet and an ordinary Siemens armature, which, by the turning of a handle, is caused to revolve between the poles of the electro magnet. The coils of the electro magnet are in circuit with the wire of the revolving armature, and during rotation the residual magnetism of the soft iron electro magnet cores at first excites weak currents which pass into the electro magnet coils, increasing the magnetism of the core, thus inducing still stronger currents in the armature wire. This accumulation by mutual action goes on until the limit of magnetic saturation of the iron cores of the electro magnets is reached. By the automatic action of the machine, the powerful current so produced is sent into the leading wire or cable to the fuze to be exploded. In this apparatus the electric current passes continuously through the line wire until a sufficiently powerful current is generated to heat or fuze the bridge of the fuze, and so ignite the gun-cotton priming. The coils of the armature and electro magnets are wound with wire of large diameter, to a total resistance of 8 to 10 Siemens units, or 7·6 to 9·5 ohms, in about 2,000 windings. With a platinum wire weighing 1·65 grains per yard, 6-1/2 inches can be fuzed on short circuit, and 14 inches can be heated to redness. The total weight of this machine, which is manufactured by Messrs. Siemens Brothers, is about 60 lbs. _Advantages of Siemens's Dynamo Electrical Machine._--The advantages of such a machine over Voltaic apparatus are:-- 1.--The absence of chemical agents. 2.--There is less liability to get out of order. 3.--No special knowledge is required to work them, or to keep them in order. 4.--Greater durability. The great defect of this and all similar machines is that the electric force has to be developed by turning a handle for a certain time before it is possible to generate a current sufficiently powerful to ignite a fuze, which defect, in connection with a system of defence by self-acting submarine mines, particularly at night, renders them inferior to Voltaic batteries, as under such circumstances, an apparatus is required that will cause an electric current to flow at any moment when the circuit is completed.