The electric wire _k k_ passes through the screw-head [= _a_] of external tube _a a_, and winding spirally around the intermediate tube _d_, terminates in a connection with the insulated bridge _p_ at _s_. The intermediate tube _d_ is attached to the head of the spindle _f_ at _t_. When pressure is brought to bear on the firing bolt _e_, the spindle _f_ is forced down, and carries with it the insulated bridge _p_, until the bridge touches the insulated terminal _l_. It will be seen that the long spiral spring _g_ and short spiral spring _h_ serve to support the spindle _f_, and keep the bridge _p_ off the terminal _l_ until they are forced into contact. Whilst the insulated bridge _p_ remains above the insulated terminal, the former is in constant contact with the metal bridge _u_; but this contact is broken when the metal bridge moves downward and before it makes contact with the insulated terminal _l_. When the insulated bridge _p_ is in contact with the metal bridge _u_, the electric fuze is out of circuit; and a current sent through the torpedo will return by way of the earth without firing the torpedo; but when contact with the metal bridge _u_ is broken, and contact with the insulated terminal _l_ is made, the current is directed through the electric fuze, and the torpedo fired. The priming in the tube is sufficient to rupture the tubes and ignite the charge in the torpedo. Fig. 2 shows a section of the circuit-closer, with the spiral spring slightly compressed, and the insulated bridge in contact with the insulated terminal, and the circuit closed. By dispensing with the electric fuze, and using in its place a piece of copper wire, any number of experiments may be made with an uncharged torpedo without adjustment or manipulation of any kind; it only being necessary to attach to the return wire near the battery a galvanometer or electric fuze to indicate the time of the impact. The torpedoes here described are manufactured by J. Vavasseur and Co., at the London Ordnance Works; at which establishment the inventor has every facility in the supervision of the various details in the construction of the torpedoes, buoys, and brakes. Such supervision of the torpedoes and their equipments is highly essential to secure safety and efficiency. TACTICS. Torpedo vessels should, as a rule, attack under the cover of darkness. By the experience gained in blockade running in the late American conflict, we are assured that a vessel in rapid motion can, when it is dark, pass with impunity close under the fire of hostile vessels, armed with cannon.