The general form of the Harvey torpedo is that of a box of a rectangular vertical and trapezoidal horizontal section, intended to float on end and tow at an angle from the ship’s keel. The case is generally made of copper or Muntz’s metal sheathed with wood; the upper inner edges being provided with shackles for attaching a towing-span. The body of the torpedo is also the magazine, large enough to hold from 33 to 58 lbs. of gun-cotton. The firing-bolt with its fuse attachment enters the magazine from the middle of the top or deck of the torpedo. This bolt is acted upon by a series of levers so arranged that if the torpedo strikes in any position, one of the levers will drive the bolt down and explode the fuse. In the later patterns of Harvey torpedoes there is also a small rudder attached, by which the course of the torpedo is regulated when the tow-rope is suddenly slacked. The sling is made with four legs going to the corners of the torpedo and of a length to bring the centre of effort in the right position for towing the torpedo at a good angle of divergence. The firing-bolt is so arranged that the torpedo may be fired in three different ways: electrically on contact, mechanically on contact, or electrically at will. The mechanical arrangement is an ordinary chemical fuse placed in the firing-bolt in connection with a small vial of sulphuric acid. When the firing-bolt is forced down by the contact of the levers with any resisting substance, the vial is broken by coming in contact with a stout needle and the acid ignites the fuse. For firing electrically at will, a platinum-wire fuse is used; one terminal going to earth at the torpedo, and the other passing through the firing-bolt and attaching to the insulated wire core of the tow-rope leading aboard ship. To fire on contact electrically, a resistance-coil is introduced in the circuit at the fuse in such a manner that by forcing the firing-bolt down the resistance-coil is cut out of the circuit and the fuse is fired by the short circuit. The firing-bolt is fitted to act with a pressure of from 30 to 40 lbs. on its head, and under ordinary circumstances is secured by a key in the ordinary manner of keying bolts. If these torpedoes are left to sink of themselves, they will explode at a depth of about 60 fathoms from the pressure of the water on the head of the bolt. In order to hold the torpedo steady when towing, it is provided with cork buoys which tow astern of it. The buoy-rope is rove through a ring at the after-end of the torpedo, and has an eye spliced in its end to which the tow-rope knots after reeving through the eye of the sling.