Circuit Breaker.—By altering the mode of connecting the wires, the above apparatus may be used as a circuit breaker, that is to say, the signal may be given, and the mine exploded by the cessation of a passing current, instead of by the closing of the electric circuit. This system was specially designed for use with platinum wire fuzes, but is rarely used.
Circuit Closer of Electro Contact Mines.—When the inertia circuit closer is employed in connection with electro contact mines, the circular ebonite piece m is replaced by a similar shaped piece of brass, and which is in metallic connection through the brass pillars l, l, l with the mass of the metal of the apparatus which forms the earth plate.
The insulated wire of the base plug is connected to one pole of a platinum wire fuze, the other pole of which is connected by another wire to the outer metal rim of the disc of the spindle. As long as the circuit closer remains undisturbed, a break will remain in the circuit, which is due to the ebonite insulation between the spindle and the outer metal rim of the disc; but the moment the apparatus is struck, which causes the spindle to vibrate, the outer metal rim will come in contact with one of the springs completing the circuit, through the circular metal portion and the pillars of the circuit closer to earth.
Adjustment of Circuit Closer.—The sensitiveness of Mathieson's inertia circuit closer is determined by the distance between the disc 4 and the springs 5, 5, 5, which is regulated by means of the adjusting screws 7, 7, 7, which press against the inner faces of the springs. Owing to the great weight of the leaden ball, when by any cause the circuit closer is inclined for a length of time, a permanent set is given to the spindle, thereby destroying the adjustment of the instrument.
Improvements in the Inertia Circuit Closer.—To remedy this very serious defect, a cylinder of india rubber is substituted for the leaden ball; a circuit closer so fitted is also less affected by the action of counter mines, which is a very important advantage.
Mathieson's Spiral Spring Circuit Closer.—A sectional elevation of this form of circuit closer is shown at [Fig. 57]. It consists of a brass base a, provided with a grooved flange for carrying a gutta percha washer, and it has also an hexagonal projection for the purpose of screwing the circuit closer into the gun-metal mouth of its air-tight cylinder, or buoy; b is a brass dome enclosing the apparatus for the purpose of protecting it from injury, and also by means of india rubber washers to prevent an ingress of water, should the circuit closer case become injured, and leak; c is a brass collar to which the brass contact springs i, i are attached, and which are regulated by the set screws j, j; a brass spiral spring d carries a metal rod e, which supports a brass ball f, surrounded by an india rubber band h. A contact disc g is secured to the base of the spindle e, but insulated from it by an ebonite boss; k is an ebonite base plug with two channels in it, through which the wires m, m1 pass.
An Improvement on the Inertia Circuit Closer.—This instrument is a vast improvement on the inertia apparatus previously described, being more simple and more certain in its action, a desideratum in all circuit closers; but notwithstanding, up to the present time Mathieson's inertia apparatus has been used by our government, to the exclusion of all other instruments of a similar nature, some of which were proved to be far superior when subjected to the crucial test of actual practice.
Austrian Self-acting Circuit Closer.—This form of circuit closing apparatus, which is purely a self-acting one, that is to say, a mine so fitted cannot be fired at will, is shown at [Fig. 58].
It consists of several buffers a, a, a, which by means of strong springs are held in position, their heads projecting outside the torpedo case b; on being pressed in by the contact of a passing vessel, the ends of these buffers would be forced against a ratchet wheel c, which is also kept in position by means of a spring. Several strong pieces of wood d, d within the case keep the buffers and their attached arms in the proper direction, and also afford rigidity to the torpedo case. The brass ratchet wheel c being put in motion carries round with it a central arrangement e, the lower part of which is shown at [Fig. 58], A.
This portion consists of a cylinder of brass f divided into two parts insulated one from the other by a piece of ebonite g; on one side of this cylinder there are three arms of brass, h, i, and k, and on the other there are two arms, l and m, all of which are insulated from each other.