It consists of a barrel a, which is thoroughly coated inside and out with hot pitch, etc., to make it watertight, a block of wood b, secured to the top of the cask a, and having a recess cut in it to receive a round shot c, also a hole through which a strop d, is passed, and another hole to receive a toggle e. At the bottom of the cask on the inside, is fixed a wooden frame work f, f, to the top of which two ordinary gun friction tubes are fixed g, g. A piece of wood h, is secured to the bottom of the cask on the outside, bored with two holes, one to receive a thin iron rod i, the other for the safety pin k. Wires x, x, secure the gun tubes g, g, to one end of the iron rod i, the other end of which is connected by means of a rope lanyard to the shot c. Weights are slung beneath the barrel to keep the mine upright. The principle of action of this form of mechanical mine is precisely similar to that of Captain McEvoy's improved Singer's mine, and need not, therefore, be described.
McEvoy's Mechanical Primer.—A sectional view of this apparatus is represented by [Fig. 14]. It consists of two brass tubes fitting accurately one within the other, of which a, a, is the inner one. To this inner tube are affixed two brass diaphragms b, b. A brass spindle c, carries a weight d, which is regulated by a spring, e. A locking rod, f, moves in a ball and socket joint at g. A hammer h, which is shown in [Fig. 14], at full cock, is kept in that position by the rod f. A vessel, striking the mine, in which this apparatus is placed causes the weight, d, to cant over, allowing the rod, f, to be forced upwards by means of the spring e, and so frees the hammer h, which falls on a nipple i, on which is placed the percussion substance, and so explodes the mine.
McEvoy's Papier Maché Safety Plug.—To prevent a premature explosion during transport, etc., of a mine in which this apparatus is placed, a plug of papier maché, which is soluble in water, is inserted in the two spaces p, p, by which the spindle c, is prevented from moving to one side or the other. The use of a papier maché, instead of a cement plug for the purposes of safety, is a great improvement, as by the simple process of pressure, any period of time that it is necessary should elapse before the complete destruction of the plug, can be readily and certainly obtained, which when a cement plug, formed of different ingredients is used, is not always the case.
McEvoy's Mechanical Mines.—Captain McEvoy has also devised a plan, whereby a mechanical mine of the foregoing form may be placed in a state of safety, even after it has been rendered active. In the place of the aforesaid papier maché wad at p, [Fig. 14], he uses a plunger which fits into the cavity p, of the heavy weight d. This plunger is always kept in a position clear of the weight by means of a spiral spring, unless it is desired to render the mine inactive when the plunger is forced into the aforesaid cavity and kept there by means of a pin inserted above it. Above this there is another plunger, acted on by a spiral spring sufficiently powerful to enable it to force the previous mentioned plunger into the safety position; this upper plunger is rendered inactive by means of a pin. The mine being placed in position, that pin which is keeping the lower plunger inserted in the cavity p, of the weight d, is withdrawn and the mine rendered active. To the pin of the upper plunger is attached a line which is anchored some distance from the mine in a known position. Then to render the mine inactive for the purpose of picking it up, etc., it is only necessary to raise the aforesaid line, and draw out the pin of the upper plunger, which by means of the strong spiral spring will force the lower plunger into the safety position, and render the mine inactive.
Whether this invention is a practicable one or not, remains to be proved, but anyhow it is a step in the right direction.
EXTEMPORE MECHANICAL MINE, MECHANICAL PRIMERS.
Abel's Mechanical Primer.—This is shown in section and elevation at [Fig. 15] (A and B). a, a, is the powder chamber in which the priming charge is placed; b is a screw plug to close the chamber; c is a flexible india rubber tube; d, d, are screw bands; e is a glass tube containing oil of vitriol enclosed in a lead tube; f which contains the explosive mixture; g, an eye at the head of the primer to receive the firing line; h, h are segmental guards; i is the guard ring; and j the safety screw pin. This apparatus is screwed into a socket in the upper part of the torpedo case, as shown at [Fig. 15] (C).
Mode of Action.—When placed in position, to render the primer ready for action, the guard ring, i, is pulled off, first having removed the safety pin j, when the segmental guards h, h, will fall away, leaving the india rubber tube c, c, exposed.