_Steward's Safety-Cock Arrangements._--To obtain security to a certain extent in placing mechanical submarine mines in position, which, as has been previously stated, is one of the defects common to all forms of such torpedoes, many ingenious methods have been devised, such as safety caps to their fuzes, safety pins, soluble plugs, &c. Another method, suggested by Captain Harding Steward, R.E., which it is intended should be used in connection with the other safety arrangements, is shown at Fig. 18. It consists of a stop-cock _A_, which, in connection with a tube, is introduced between the fuze and the charge. It is so arranged that when the cock is turned in the direction of the tube, as shown in section _B_ at _e_, the gas on formation can pass easily through and explode the charge; but when the cock is shut off, the gas on formation escapes through the side _d_, as shown in section _C_. To prevent destruction of the charge through leakage under the pressure of the water, the cone in connection with the stop-cock should fit very accurately, and, as an additional preventive, the escape hole should be covered with a waterproof plaster, which at a moderate depth would keep the water out and yet offer no material resistance to the escape of the gas if the stop-cock were shut off, as at _C_. The efficiency of this arrangement, as far as relates to its cutting off the gas from the charge, has been satisfactorily proved by practical experiments. _Mooring Mechanical Mines._--This description of defensive torpedo will rarely be used in deep-water channels, &c., and on account of the impossibility of ascertaining whether such a mine has drifted or otherwise, it should not be moored in a very rapid current. Such being the case, an ordinary mushroom anchor, heavy stone, &c., and single steel wire mooring-rope, will be generally found quite sufficient to keep such mines in position. When only a few mechanical submarine mines are moored in position, and at some distance apart, it would be found a useful plan to moor them each with three anchors, one anchor being up-stream. By this method, at low water, on the up-stream anchor being raised, the mine would show itself, and might in that position be approached and rendered inactive. Were this plan to be adopted when several such mines are in position, there would be the danger of the up-stream anchor on being raised, bringing up to the surface, and probably in contact with the boat at work, a mine to which that particular anchor does not belong, an explosion being the result. FOOTNOTES: [Footnote I: "Submarine Warfare," by Commander S. Barnes, U.S.N.] CHAPTER III. DEFENSIVE TORPEDO WARFARE--_continued_. BY electrical submarine mines is meant those whose charges are ignited by the agency of electricity.