A percussion fuse is one in which the flame is produced by a blow on some fulminating compound. Of such a type is the fuse of the Whitehead torpedo, which in principle is precisely that of the firing arrangement of breech-loading small-arms. The shock on the nose of the torpedo starts it back, releasing the firing-pin spring, which driving against a cap or fuse of fulminate, explodes it. The fuse of Singer’s torpedo cannot depend directly on the shock of collision to explode it, as the shock might be very light. As an intermediary, therefore, the heavy cover of the torpedo is used, which falls off when the torpedo is tilted, and by its descending weight releases the lock mechanism. This consists of a firing-pin and spring secured vertically underneath the torpedo and held retracted by a small pin. This pin is withdrawn by the falling cover, permitting the firing-pin to drive forward against the bottom of the torpedo. Just over the spot where it strikes is a short rod travelling in guides, the upper end being in contact with a small capsule of fulminate, which is exploded by the shock of the outside pin. _The Torpedo Time-Fuse_ is in principle a lock mechanism in which the firing-pin catch is in connection with a train of clockwork. This clockwork being set to run for a certain length of time, the torpedo is set adrift to float against the vessel or obstruction, and the torpedo explodes at the end of the time for which it is set. The original and most crude form of this type of fuse is a candle cut to a certain length, the bottom being connected to a quick-match. It is not in this case a percussion fuse, as the quick-match communicates directly with the charge. [Illustration: Clockwork Fuse.] _McEvoy’s Fuse_ consists of a percussion system in connection with a small propeller. As long as the torpedo drifts with the current the propeller does not revolve, but if it is brought up in any way the force of the current starts the propellers, which after a few turns release the firing-pin spring. The torpedo by means of which the Albemarle was sunk (see cut, page 335) was exploded by a percussion fuse of still a different nature. The torpedo itself was attached to the end of a spar, but just before explosion it was intended to detach and capsize. A hollow tube passed through the axis of the torpedo, having at the nose-end an ordinary percussion-cap arrangement. The rear half of the torpedo formed an air-chamber, and at the rear end of the tube an iron ball, free to move along the tube, was held in place by a small pin to which a laniard was attached to be pulled by hand. The torpedo being thrust by the spar under a vessel was detached, and the air-chamber caused it to tumble bottom up immediately. The pin then being withdrawn by the laniard, the ball dropped on the percussion-cap and fired it. [Illustration: McEvoy’s Propeller-Fuse.] [Illustration: English Dynamo-Electric Fuse.] _Hill’s Fuse_