- 1.—The self-acting method.
- 2.—The firing by judgment, or observation method.
During the early days of submarine defensive warfare, the latter method alone was used, owing to the absence of anything like a practicable form of self-acting apparatus; but within the last few years, the former has almost entirely superseded the latter method, except in very exceptional cases; this revolution being due to the vast improvements that have been, and still are being effected in the system of firing electrical submarine mines automatically.
Use of Circuit Closers.—Electrical submarine mines may by means of an apparatus, termed a circuit closer, be rendered self-acting; that is to say, by the action of a vessel coming in contact with such an apparatus, which may be either within the mine itself, or within a buoy attached to the mine, the electric circuit is closed, and the mine in connection with the circuit closer so struck, exploded. The essential feature of such a mode of closing the electric circuit is, that electrical submarine mines may be rendered either active or harmless, at the will of the operator, which is effected by the putting in, or taking out of a plug, by which means the firing current is either thrown in, or out of the circuit.
Circuit closers.—Many different forms of circuit closers have been devised, among which the following seem the most suitable and are those generally used:—
- 1.—Mathieson's inertia circuit closer.
- 2.—Mathieson's spiral spring circuit closer.
- 3.—Austrian self-acting circuit closer.
- 4.—McEvoy's mercury circuit closer.
- 5.—McEvoy's weight magneto circuit closer.
Mathieson's Circuit Closer.—This form of circuit closer has been adopted by the English government in connection with their system of defence by electrical submarine mines.
The details of this apparatus are shown at Pl. xiii.
[Fig. 53], a is a gun-metal dome screwed on to a metal base b, its foot resting on a gutta percha washer c, so as to exclude any water; d is a cap screwed on to the top of the dome, and made watertight by the leather washer e; f is a guard cap screwed into the cap d, this is to keep the spindle of the circuit closer steady during transport, and would be removed when the apparatus is prepared for service; g is the ebonite base plug through which pass the insulated wires E and L; h is an hexagonal collar, working in the metal base plate b, by means of which, and the brass collar i, and the leather washer k, the base plug is secured, and water is excluded from the interior of the circuit closer; l, l, l are brass columns supporting a circular ebonite piece m; n is a metal bridge screwed on to the base plate b, into which is screwed the spindle p, both of which are prevented from moving after being screwed up by the set screws r and s.
The spindle p carries a leaden ball t, which is supported upon the rest v, and is secured in position by the screw nut w; x is an india rubber ring, the object of which is to prevent any damage being done to the spindle should the ball when set in action by a heavy blow from a passing vessel be brought into contact with the dome; 2 is a brass disc attached to the spindle carrying an ebonite disc 4, connected to it by screws; 6 is a brass contact ring also fixed to the ebonite disc 4, provided with a screw 8, for the attachment of one of the base plug wires, and with platinised projections 3, 3, 3, [Fig. 56]. The contact ring 6 is completely insulated from the spindle and brass disc 2. Three contact springs 5, are attached to the circular ebonite piece m, and the faces opposite to the platinised projections of the disc 2 are also platinised. 7 shows the contact screws of the connecting pieces, which serve also as adjusting screws to regulate the sensitiveness of the apparatus, the points of which as well as their bearings on the springs are platinised.