When this form of circuit closer is put in action by a friendly vessel coming in contact with it, or when experiments are being made, the signalling current must be reversed, so that no doubt may exist as to the armature n having dropped, on the apparatus coming to rest.
The telephone test indicates whether the circuit closer is in position or not, the shot, &c., within the telephone being shaken about by the movement of the buoyant circuit closer, the noise so created is readily distinguished by the receiving telephone at the station.
Another form of submarine mine is that known as the "Electro Mechanical" mine. The difference between this form and an ordinary mechanical mine is, that the exploding agent is electricity, and that it may be converted into an electro contact mine if desirable.
Description of a Russian Electro.—The electro mechanical mine, used by the Russians during the late Turco-Russian war, is shown in elevation and section at [Fig. 62] and [63].
Mechanical Submarine Mine, used by them during the late Turco-Russian War.—A is the conical shaped case; B the loading hole; C the base plug; D, D, &c., are five horns, screwed into the head of the case A; these are composed of a glass tube A, containing a chlorate of potash mixture, enclosed in a lead tube B, over which is screwed a brass safety cylinder C; when ready for action this latter tube C is removed; directly beneath each of the horns A, on the inside of the case, as at E, is a thin brass cylinder, closed at one end by a piece of wood d, and containing several pieces of zinc and carbon, arranged in the form of a battery, the zinc and carbon wires z and x being led through the piece of wood d; F is a copper cylinder containing the priming charge of gun-cotton g, and detonating fuse f; the terminals of the fuze are connected to two insulated wires, w and w1, the former of which is led direct to the loading hole B, and attached on the inside to the five zinc connecting wires z, &c.; the latter is attached to one end of a safety arrangement S, the other end of which is connected to the wire w2, which is attached on the inside to the carbon wires x, &c.; the safety arrangement S consists of an ebonite cylinder, containing a brass spiral spring fixed to one end of it, and pressing against a brass plate at the other, thus preserving a metallic connection between the wires w1, and w2; the mine is rendered inactive by pressing the spring down, and inserting a piece of ebonite between it and the plate.
Its Action.—The action of this form of electro mechanical submarine mine is very simple; the brass safety cylinders c, c, &c., being removed on a vessel striking either of the horns, D, D, &c., the lead tube b is bent, causing the glass tube a to be broken, and the mixture contained therein to flow into the cylinder E, instantly generating a current of electricity in the zinc carbon battery, and exploding the mine.
Mode of Converting into an Electro Contact or Observation Mine.—To convert this mine into an electro contact one, it is only necessary to connect the wires w1 and w2 to other wires leading from the shore; also by replacing the horns D, D by solid brass screw plugs, the mine may be converted into an ordinary observation one. In this case the two wires w and w1 attached to the fuze f, terminals would have to be connected to the observation instruments on shore.
Turkish Vessel sunk.—It was by means of one of these electro mechanical mines, that the Turkish gunboat Suna was sunk at Soulina.
Firing by observation, that is to say, effecting the ignition of an electrical submarine mine at the precise moment of a hostile vessel being vertically over it, through the agency of one or two observers stationed at a very considerable distance from the mine, should, with the very perfect self-acting circuit closers that exist at the present time, be resorted to only in very exceptional cases, or in connection with the self-acting system.