At the same time the passage of the strong firing current may fuze a connection in the junction apparatus, by which the exploded torpedo is detached, i.e. the direct "earth" connection of such a torpedo is cut off, and the remaining submarine mines are left in proper working order; this effect may also be arrived at by other means.
General Description of Apparatus.—The following is a general description of this exceedingly clever and useful invention:—
At [Fig. 168] is shown a diagram view of the apparatus.
A is the instrument at the firing point on the shore or vessel; B is the cable wire led to a submerged box situated near the spot where the several torpedoes are grouped; C is the instrument enclosed in the submerged box; D, D are insulated wires led away from the box to the several torpedoes, there being a separate wire for each torpedo.
Each of the wires D is coupled to one or other of a series of metallic contact pieces E ranged in a circle round the axis of a metallic pointer F, which can be turned with a step by step motion and successively brought into electrical contact with the several contact pieces E. The axis of the pointer is in electrical communication with the wire of the cable. The wire from the cable is first led to the coils of an electro magnet G, and thence passes to the axis of the pointer. H is a magnetic armature in front of the electro magnet G; when a positive current of sufficient strength is sent through the cable the armature is rocked in one direction, and when a negative current is sent, it is rocked in the opposite direction. From the armature motion is transmitted to a pawl which works into the teeth of a ratchet wheel on the axis of the pointer F, so that by sending a succession of reversed currents of sufficient strength through the cable, the pointer F is turned with a step by step motion and is successively brought into electrical contact with the several contact pieces E.
Mc.EVOY'S SINGLE MAIN SYSTEM
In the instrument, at the firing point a is a handle, by the turning of which a step by step motion is given to the pointer of a dial b and a simultaneous movement to the pointer F of the instrument C in the submerged box. When the handle a has made a half turn it couples one pole of the battery to the cable and the other to the earth connection, and when it has made a complete turn the connections are reversed. The pointer of the dial b then moves forward from one division of the dial to the next, and simultaneously the pointer F is turned in unison with it. The operator at the firing point can therefore always see which of the torpedoes is in electrical connection with the wire of the cable, and he can test each torpedo in succession by moving a handle, say at h, to cause the current passing back from the torpedo to pass through a galvanometer at e, and by the movement of the needle of the galvanometer it can be seen whether the resistance of the circuit through this torpedo is in its normal and proper working state.
When the pointer of the dial b is brought to zero, or as it is marked in the drawing to "signal," then the pointer F of the apparatus C is in electrical communication with a contact point which is coupled to all of the branch wires D, and usually the apparatus is left in this condition, the handle a being then locked and prevented from turning by a bolt actuated by a handle at G.