Mechanically.—In this case the bottom of the inner cylinder, as at a, [Fig. 108], is fitted with the ordinary mechanical chemical fuze, ignition being effected by the breaking of the glass vessel containing the sulphuric acid on being forced into contact with the needle n, by the action of the levers on the torpedo striking a vessel.

Electrically at Will.—For this purpose a platinum wire fuze is used, one terminal being connected to earth through the bolt, the other to a wire leading up through the core of the bolt, and connected by means of an ebonite joint with a single cored electrical cable leading from the torpedo vessel.

Electrically on Contact, or at Will.—In this case, a resistance coil is inserted in addition to the fuze, and is so arranged that on the bolt being forced down a short circuit is formed, cutting out the resistance coil (about 20 ohms), and thus enabling the battery to fire the fuze, which, owing to the 20 ohms resistance in the circuit, it was previously unable to effect. Should the bolt so arranged be required to be fired at will, it is only necessary to put a more powerful battery in circuit, and so fire the fuze through the 20 ohms resistance.

Exploding Bolt.—The exploding bolt is fitted to act with a pressure of from 30 to 40 lbs. on its head for the large size torpedo, and from 15 to 20 lbs. for the small size one.

The bolts are all the same size, and differ only in the direction of the slot for the safety key k, being port or starboard bolts accordingly. The muzzle of the exploding bolt stands 1 inch off the pin when in the safety position, that is, when the safety key rests on the brass work of the priming case.

The safety key is secured in the slot of the exploding bolt, as shown at [Fig. 108], by eight or nine parts of strong whitey-brown thread secured to the key, passed round the bolt, and securely knotted; the parts of the thread should come away with the key, in order that none of the parts may be worked down the tube by the exploding bolt.

In the event of the large torpedo being cut away in deep water after the withdrawal of the safety key, it will explode by pressure on the head of the bolt at about sixty fathoms depth; the small one at about thirty fathoms.

Buoys.—The buoys are of two sizes, and are made of solid cork (such cork only being used as will ensure great floating power after being immersed for a time); each buoy is built upon a galvanised iron tube running longitudinally through; on the ends of the tube are screwed wooden cones, which bind all together, and render the buoy indestructible.

Two buoys are used for each torpedo, the larger buoys for the large size torpedo, and the smaller buoys for the small size torpedo. The buoy rope is of hemp, about five or six fathoms in length and two inches in circumference, an eye being spliced in the end nearest the torpedo; to this eye is bent the tow rope, with a single or double sheet bend forming the knot by which the torpedo is towed; the other end of the buoy rope is passed through one of the rings in the stern end of the torpedo (according to whether working in deep or shallow water), then through the tube of the first buoy, and an overhand knot made in the rear; then through the next buoy, and a knot in the rear of that. Recently, Captain Harvey has adopted a large and a small buoy for each torpedo, the large one being practically sufficient, the smaller one being added in the event of the other one becoming sodden.