Though no accidents are stated to have occurred in placing this mine in position, yet the fact of the iron rod _c_ having to be fixed for action, and that close against the interior of the bottom of the case, before the charge of powder has been put in, is an element of great danger, for a comparatively slight blow beneath it, which might easily occur in transport, etc., would explode the torpedo prematurely. _McEvoy's Improved Singer's Mine._--To obviate this defect Captain McEvoy has designed an improved mode of ignition for Singer's mine. This is shown at Fig. 11. The form of case, and arrangement of heavy cap are similar to those in Singer's mine. The mode of ignition is as follows:--In the powder chamber _b_ is fixed a friction fuze _f_, which by means of a piece of wire secured to a length of chain _k_, _k_, is connected with the heavy cast iron cap _A B_. The piece of wire passes through a diaphragm of thin metal _h_, which is soldered all around, thus forming a complete watertight joint. Premature explosion is prevented by passing a link of the chain, through a slot in the bolt _c_, securing it there by a pin of bent wire _l_. The dotted line of chain _k_, _k_, shows its position during the process of mooring this form of Singer's torpedo. The manner of lowering this and also Singer's mine is shown at Fig. 12. A buoy _x_, is attached by means of a line, in the former case to the pin _l_, Fig. 12, in the latter case to the pin _k_, Fig. 10, the pulling out of either, sets their respective mines in action. [Illustration: SINGER'S AND M^{c}EVOY'S MECHANICAL MINES. PLATE III.] _Mathieson's Cement Safety Plug_.--In the place of the safety pin _l_, Fig. 11, employed by Captain McEvoy in his improved form of Singer's mine, Quartermaster-Sergeant Mathieson, late Royal Engineers, employs a plug or disc of soluble cement, so arranged that the action of the sea-water after the mine has been placed in position destroys the plug or disc, and so frees the chain which is connected with the fuze and the heavy cap of the torpedo. This plan does away with the necessity of using a buoy and line as shown in Fig. 12, and also affords ample time for the men engaged in mooring the mine to get far away before it is ready for action. _Mechanical Mine_.--The extempore mechanical submarine mine, shown at Fig. 13, will be found to possess all the qualities which are necessary to a perfect mine of that description. It is extremely simple, it can be readily and quickly made, all the materials of which it is constructed are at hand on board every man-of-war, and it is certain in its action.