American spar-torpedoes are of two general forms. The first, for gunpowder charges, is in the shape of a long cylinder with hemispherical ends. The second, for dynamite charges, is in the shape of a large double convex lens. The powder torpedoes have a capacity for a charge of from 75 to 100 lbs. of small-grain powder; the dynamite ones have a capacity of from 15 to 30 lbs. In the gunpowder torpedo a large hollow spindle passes through the axis, closed and secured at one end by a large nut. This spindle is pierced with flame-holes at short distances, so as to permit the flame from the fuse to penetrate and ignite all parts of the powder-charge at once. Around this spindle is a guard of wire gauze to prevent the powder from the charge sifting into and choking the flame-passages. This spindle projects some little distance beyond the inner end of the torpedo-case, forming a handle or support by which the case is attached to a spar. At the inner end on each side of the spindle is a loading-hole secured by nuts and washers. There are also four handles, two on each side of the case, for convenience in transporting. The 100-pdr. torpedo loaded and fused weighs about 360 lbs. The torpedo-fuse, which is an electric one, finds a place by itself inside the spindle, the terminal wires passing through a simple water-tight gland. [Illustration: Socket for American Spar-Torpedo.] [Illustration: Wood and Lay’s Spar-Torpedo.] [Illustration: Boat-Fittings for American Spar-Torpedo.] On the end of the torpedo-spar is lashed a cast-iron sleeve into which the end of the spindle is keyed. The torpedo-spar for use on the bows or broadsides of vessels varies in length from 20 to 50 feet, and is supported and pointed by guys and lifts in the same manner as is common with swinging spars generally. The wires from the fuse are brought in along the spar to the electrical machine and firing-keys arranged in suitable positions. The spars used in boats are generally arranged on a different principle from those attached to the bows or beams of high-sided vessels. Arranged to work in a swivelled sleeve with a martingale at the rear end to regulate the depth to which they shall sink, the spar is either launched or dropped over and is permitted to swing without guys, the operator watching and exploding it as it is brought abeam and into the desired position by the driving ahead of the boat. [Illustration: Fitting for Heel of Spar Ship-Torpedo.] [Illustration: Chafing-Plate for Heel of Spar-Torpedo.] The spar used with the dynamite torpedo is an iron or steel bar of diminished cross-section in order to offer a minimum resistance to the water, with a hinged piece at its rear end bolting to the keelson of the boat and acting as a martingale. TORPEDO VESSELS. In several of the navies of the world gun-boats have been designed for the purpose of using torpedoes, either locomotive or spar, to the total exclusion of battery—or, in some cases, with a limited artillery—fire.