When a hollow steel spar is used, the battery wires are sometimes led through the interior of the torpedo and the spar, by which means they are well protected; the only objection to this method of leading the wires being the probability of injury to them, should the spar be broken on contact, or by a shot.
_McEvoy's Arrangement of Torpedo Wires._--At Fig. 143 is shown the arrangement of wires as devised by Captain McEvoy, whereby the spar torpedo may be exploded at will or on contact. _c_ and _z_ are the poles of the firing battery, to which are attached respectively the wires _d_ and _d_^{ 2}; _f_ is the fuze, which is placed in the centre of the charge, and to the poles of which the wire _d_^{ 2} is attached, the other end of this wire being connected with the stud _s_; to the stud _s_^{ 1} is attached the other end of the wire _d_, and at the point _c_ in the same wire is inserted a contact breaker; another wire _d_^{ 1} is connected to the wires _d_ and _d_^{ 2} at the points _r_ and _r_^{ 2} respectively, and at the point _k_ in this same wire is inserted a firing key, which latter is shown in section at Fig. 144, from which the mode of connecting the two ends of the wires and of using the key will be at once apparent. The contact breaker is somewhat similar to the firing key, but there is no spring in it, contact being made or broken by screwing the two parts together or apart. The object of the contact breaker is to prevent the torpedo being exploded by contact, and so to place the control of the weapon entirely in the hands of the operator. As will be seen from Fig. 143, if contact is broken at _c_, it is impossible to fire the torpedo unless the firing key _k_ be pressed in; but should contact be made at _c_, then either by means of the firing key _k_, or by the torpedo striking the hostile vessel, its ignition will be effected.
The foregoing method of arranging the spar torpedo wires is certainly very neat and effective, and is at the present time in extensive use. As yet it has not been adopted by the English government, they still preferring to fire the spar torpedo at will alone.
The different methods of manipulating the spar torpedo from boats will be described in the following chapter.