A double steering-rudder is used, one half being above and the other below the line of the propellers; these rudders are worked by means of a small auxiliary, engine, which is started, stopped, and reversed by means of the electrical current. The current passing in one direction starts the engine ahead, putting the helm to starboard. If the current is broken, the engine stops and the rudder swings amidships. The current passing in the opposite direction reverses the engine and puts the helm to port. In the firing circuit there are two resistance-coils, one in the boat and one by the operator; the charge may be fired through either one of the coils, but not through both. When the nose of the torpedo strikes a resisting object the coil in the boat is cut out of circuit and the charge is exploded. If the operator desires to fire before striking, he can at any moment cut the coil near him out of the circuit and thus fire. The propelling engines have a throttle-valve which controls the admission of gas from the reservoirs to the cylinders, the valve being in connection with a balanced lever. The current passing one way draws down one end of the lever, opening the valve, and passing the other draws the other end down, closing it. In one modification of this torpedo the forward compartment or magazine is made detachable, so that on striking an object it breaks adrift and sinks a short distance before exploding, thus gaining the best depth of water. In launching these torpedoes from a vessel, a tube is provided opening below the water-line and being provided with a forward water-gate and a rear loading-door. The torpedo being put in place, the rear door is closed, the gate raised, admitting the water, and the torpedo launches itself after the engine is started. In order to sink or raise the boat, a water-chamber is supplied having a valve for admitting outside water and another for the admission of gas. By sending a current one way, the water-valve is opened and water is admitted until the torpedo is sunk to the required depth. By sending the current the other way, the gas-valve is opened and the pressure of the gas forces the water out and the torpedo rises. The Lay torpedo may be used for clearing river obstructions, by laying out small charges in any position or by dragging a grapnel. In the latter case, an exploding charge is attached to the upper end of the grapnel-chain. When the grapnel holds fast to any obstruction the operator is notified, and by means of an electrical current he detaches the charge, which slides down the grapnel-chain and explodes at the obstruction, blowing it away. TOWING TORPEDOES. _The Harvey Torpedo._ [Illustration: Harvey Torpedo.] [Illustration: Towing-Reel.] [Illustration: Levers.] [Illustration: Firing-Bolt.]