AUSTRIAN CIRCUIT CLOSER, MERCURY CIRCUIT CLOSER.
The arm h is close to, but insulated from a metal plate n, which latter is permanently connected with the conducting wire leading from the firing battery, and thus while in a state of rest is electrically charged; beyond the arm i is a spring o, which is connected with the earth, and in such a position that when the central portion is moved round, this spring o comes in contact with the arm i, and the plate n with the arm h simultaneously, and the circuit is thus completed through earth to the battery, but the current of electricity does not pass through the fuze. The arms k, l on the opposite sides of the cylinder, and consequently insulated one from the other, are connected with the fuze, and the arm m is connected with the earth.
On a further pressure of the vessel on the buffer, the arm i is pushed beyond the spring, and in contact therewith, and consequently the circuit by earth to the battery is broken, while the contact of the arm h and plate n is still retained, and the current is passed by the arm k through the fuze to the arm l, and then to earth through the arm m, thus completing the electric circuit of the firing battery through the fuze, and to exploding the mine.
The spring acts as a circuit breaker, and by means of an intensity coil in connection with the firing battery, the current is only passed through the fuze when at the point of greatest intensity.
By detaching the firing battery, the channel defended by such submarine mines may be rendered safe.
Fuze only in Circuit at Moment of Firing it.—One of the principal objects to be gained by the employment of such an arrangement for the closing of the electric circuit in connection with submarine mines, is the prevention of premature explosion from induction which might be caused by the proximity of any atmospheric electricity, the fuze in this system being entirely cut out of circuit until the moment when it is necessary to fire it.
The Austrians employed this form of circuit closing instrument during the war of 1866, and still continue to use it in connection with their coast defence by submarine mines.
McEvoy's Mercury Circuit Closer.—At [Fig. 59] is represented a longitudinal section of a circuit closer of this construction.