_Description of Lewis's Drifting Torpedo._--"Lewis's" drifting torpedo, designed for the express purpose of destroying booms or other floating obstructions placed round a vessel at anchor for the purposes of defence, is shown at Fig. 101. It consists of a box _a_, containing the charge and fitted with several detonating fuzes. This box is attached to one side of a beam _b_, and within 6 inches of one extremity, the beam being about 20 feet long and 7 inches square; to the opposite side, of the same end of the beam _b_ a heavy weight _c_, resting in a shoe _d_, is attached by a long iron rod _e_, which reaches to the other extremity of the beam, and is there connected to a bell-crank lever and spring _f_, a pressure on which detaches the weight _c_; a chain _g_, 18 feet long, connects the weight loosely with the upper end of the beam, and another chain _h_, 9 feet 6 inches long, connects it with a point more than 2 feet below the centre of the beam. The apparatus is so constructed that it floats nearly vertical with the top of the beam just above the surface of the water. On the machine drifting against the boom or other obstruction, the spring or lever _f_ at the upper extremity is pressed down, thus releasing the weight _c_, which falling, becomes suspended by the two chains _g_ and _h_, and brings the beam into an inclined position. The weight of this mass of iron and the chain suspending it are suddenly brought to bear on the top of the beam, dragging it under water and clear of the boom, &c. At the same time the lower end, released from the weight, rises, and the whole apparatus is carried forward by the current against the side of the vessel, on striking which the torpedo is exploded. _Description of McEvoy's Drifting Torpedo._--"McEvoy's" drifting torpedo is intended to be floated, singly or in groups, by the aid of tides or currents against vessels at anchor, bridges, &c. At Fig. 102 is shown a plan of this form of drifting torpedo. It consists of the body of the torpedo _a_, which contains the charge, at the side of which is placed the loading hole _b_; _c_ is the tube containing the priming charge; _d_ is the framework surrounding and protecting the wheel or screw _e_; _f_ is the fuze pillar, in the centre of which is a steel rod _g_, and on the top a thin steel plate _h_ is placed; _i_ is the nipple for the percussion cap; _k_ is a horizontal bar, turning and resting on top of the fuze pillar _f_; _m_ is the lever for supporting the hammer _n_ when it is set; _l_ is the screw barrel supporting the wheel or screw _e_; _o_ is a safety pin; _q_ is the supporting chain, and _p_ the spring for working the hammer _n_. By means of a buoy or log of wood, from which the torpedo is suspended, it can be adjusted so that the explosion shall occur at the requisite depth.