The charge in the magazine can also be fired at any moment by the operator on shore closing a circuit on the keyboard and thereby cutting out one of two resistance coils placed in the circuit to prevent accidental or premature discharge--that is to say, there are two resistance coils. The battery is not sufficiently powerful to fire through both resistance coils at the same time. When the boat strikes an object, the resistance coil in the magazine is cut out by the driving inward of the rod _V_, as above described; the battery then fires through the one on the keyboard. On the other hand, if the operator desires to fire the torpedo boat before she touches the object of attack, he manipulates the switch to cut out the coil in the keyboard, the charge then being fired through the coil in the magazine. This arrangement of the two resistance coils is very effectual in preventing accidents.
In some instances the magazine is made detachable from the hull of the boat, so that on striking an object it will descend or drop down in the water before exploding. This modification is shown at Figs. 125 and 126.
The magazine _A_* is attached at its lower side to the boat by a chain or other suitable connection. At its upper edge it is held by a rod _a_*, as shown in Fig. 125. This rod is fitted to slide in dovetailed bearings, as shown at _b_*, and when this magazine is in its place on the boat the said rod is engaged with a catch or stop _c_*, but when the said rod is driven against any object it is forced back and released from the said catch or stop, and the magazine then drops, as in Fig. 126, and is fired.
To effect the firing a ball _d_* is used and placed in a tube containing two springs or plates _e_* and arranged in an upwardly inclined position, as shown in Fig. 125, one of the said springs being connected with the cable and the other with a wire that passes through the cartridge to earth.
While the magazine is in the position shown in Fig. 125 the circuit is incomplete, but when the magazine drops the said ball falls into the position shown in Fig. 126; the circuit is then completed, and the magazine is fired.
The electrical or electro-magnetic apparatus for generating, directing, and controlling the currents, whereby the above-described operations are effected, may be of any suitable kind, the following being the form of apparatus usually employed.