_a._--BARREL MINE. _b._--BROOK'S MINE. 3.--SINGER'S MINE. 4.--MCEVOY'S IMPROVED MINE. 5.--EXTEMPORE MINE. _Frame Torpedoes._--This form of defensive mine is shown at Fig. 6. It consists of a frame work which is formed of four strong timbers _a_, _a_, _a_, _a_, these being kept parallel and only a few feet apart by means of cross timbers _b_, _b_. A cast-iron torpedo _c_, _c_, _c_, in the shape of a shell, is bolted to the head of each of the timbers _a_, _a_, _a_, containing about thirty pounds of fine grained gunpowder, and fitted with a percussion fuse, which is so placed that it would come into contact with a vessel striking against the framework, directly or not. One end of the frame is securely anchored, the other, that on which the torpedoes are fixed, is kept at its proper distance below the surface of the water by means of chains, _d_, _d_, and anchors. To prevent the frame from sinking when sodden with water, the uprights _e_, _e_, are provided. This form of mechanical mine, which performs the double function of torpedo and obstruction, was much used by the Confederates, and found extremely useful, no passage was attempted to be forced by the Federals where these torpedoes were known to be placed. _Stake Torpedo._--Fig. 7 represents another form of the frame torpedo. It consists of a piece of timber, _a_, its heels secured by a heavy metal shoe _b_, working in a universal joint in the mooring, _c_. At the head of the piece of timber is secured a torpedo _d_, containing about fifty pounds of gunpowder, and fitted with four or five sensitive fuzes. The proper angle of inclination is obtained by securing the upper end of the timber to an anchor as shown at _e_. As a proof of the efficiency of this species of mechanical mine, even though having been in position for a great length of time, the U.S. gunboat, _Jonquil_, was nearly destroyed whilst attempting to remove some similar torpedoes which had been in position for two years. [Illustration: FRAME TORPEDOES, BUOYANT MECHANICAL MINES. PLATE II.] _The Barrel Torpedo._--One description of this form of mechanical submarine mine is shown at Fig. 8. It consists of a barrel _a_, to the ends of which are attached two cones of pine _b_, _b_, for the purpose of preventing the current from turning the mine over. To ensure its being watertight, pitch is poured into the interior through the bunghole, and the barrel rolled about, so that the inside may be evenly covered. The outside was also thoroughly coated with pitch. These mines usually contain about 100 lbs. of gunpowder, and are exploded by means of percussion or chemical fuzes (_c_, _c_, _c_,) generally five in number, screwed into sockets on each side and on the top of the bilge of the barrels. To keep them upright a weight _d_ is hung below the mine. This kind of mechanical mine was much used by the Confederates, and to some extent by the Turks in their late war with Russia.