When prepared for use, the platinum wire bridge g is surrounded by some loose gun-cotton priming, sufficient in quantity to blow off the boxwood cover f, without destroying the dome a; the cover f being blown off, carries the ebonite pin h with it, and through the platinum wire bridge g, thereby rupturing it, and breaking the continuity of the circuit. The object of so doing is to cut off the connection of an exploded mine, so that the full amount of the firing current is available for the other mines, and not suffered to be wasted by passing through the exposed wire of the broken circuit, which, were the disconnector not employed, would be the case.
When any particular mine of a system is struck, the current passes through the main cable b, the disconnector a (which is in connection with that mine), and branch cable b' to the fuze, and so explodes the mine, and destroys the platinum wire bridge g of the disconnector at practically the same instant. The effect of the latter operation would be to cut off and insulate the branch cable of the exploded mine, and so prevent any loss of the electrical current, when another mine of that system is required to be fired.
The platinum wire bridge g is 4/10 inch long, while that of the fuze is 3/10 inch, the object of this difference in length of the bridges being to ensure the former one g being fired, and thus the insulation made doubly sure. Many other forms of disconnectors have been devised, but none have proved in practice so effective as the one just described.
JUNCTION BOXES. MECHANICAL TURK'S HEAD.
Mooring Electrical Submarine Mines.—This is one of the most difficult problems to be solved in connection with a system of submarine mines. The objects to be attained in mooring are as follows:—
1.—The mines should preserve the exact positions in which they are laid down.
Note.—From the comparatively small radius of destructive effect, of even heavily charged submarine mines, it will be understood how absolutely essential, in the case of mines fired by judgment, it is that this object should be attained.
2.—The mooring chains, or ropes, must be so arranged that no twisting whatever should occur, as otherwise fracture of the insulated wire would be likely to happen.