Each of these pole changers is arranged to effect and control one of the above-named operations, and is therefore connected with one of the aforesaid insulated wires forming the cable. For instance, the pole changer _s_^{1} effects the starting and stopping of the propelling engine; _s_^{2} controls the steering apparatus; _s_^{3} is connected with the steering index; _s_^{4} operates or adjusts the aforesaid guiding rods; and the switches _s_^{5}, _s_^{6} control and effect the firing of the charge in the magazine. [Illustration: LAY'S LOCOMOTIVE TORPEDO. PLATE XXXVIII] [Illustration: LAY'S LOCOMOTIVE TORPEDO. PLATE XXXIX] The connections between these pole changers and switches, and the apparatus they operate or control on board the boat, are as follows--that is to say, the said propelling engines have a throttle valve, which controls the admission of the gas from its generator or reservoir to the cylinders of the said engine, and in combination with this valve in the boat there is a shunt and set of electro magnets. The armature of the latter is connected with a lever, which is pivoted so that the action of the electric current in one direction through these magnets will pull one end of the said lever down, and the action of the current in the other direction will pull its other end down--that is to say, by reversing the current through these magnets the movement of the said lever is reversed; and this lever, connected by suitable means with the slide of the said throttle valve, will open or close the same, and thereby start or stop the engine as required.