Broadly speaking, there are three different kinds of submarine mines. First, observation mines, which are fired from the shore when a ship is known to be in range; second, automatic mines, which are exploded on being struck by a ship, which is the kind with which the Russians claim that the "Petropavlovsk" was sunk; third, electric-contact mines, which on being struck by a passing vessel give notification to an operator on shore, who fires the mine by the throw of a switch.

The accompanying illustrations show a system of electric-contact ground mines, laid across a channel, with a battery of rapid-fire guns on shore so placed that they command the whole of the mine field, and render it impossible for the small boats of the enemy to attempt to explode the mines before the big battleships and armored cruisers pass over them. The battery is placed rather low down near the water, and above it is a battery of heavy 8 and 10-inch breech-loading rifles mounted either en barbette, or on disappearing mounts, while above these, carefully masked by shrubbery, is a firing station, which is connected by cables with the mines in the channel. Sometimes, by preference, the firing station is placed in a massive concrete casemate, which is built into the structure of the fortification. The submarine mines would be laid out in a series of parallel lines, and so. spaced that the mines in each line would cover the spaces left in the adjacent lines, with the result that on whatever course a ship might be steering, she would be certain to strike one or more of the mines before she passes over the field. The ground mine, which, as we have said, is usually a hemispherical metal case, contains several hundred pounds of high explosive, and is held in place on the bed of the river or channel by its own weight, sometimes assisted by heavy hooks cast upon the outer shell. Anchored to the mine, and floating above it, at a depth below water that is less than the draft of the enemy's vessels, is a hollow buoyant sphere in which is placed the electric circuit-closer. The second engraving of the two herewith shown represents a section through the floating sphere, and shows the details of a type of circuit-closer which has been very widely used. It consists of a horseshoe magnet, M, M, within which is hung by a coiled wire a ball, B. A silken cord is hung from the top of the magnet, passes down through the ball, and is attached to an armature, A. When the vessel strikes the buoy, the ball is thrown to one side, draws aside the silken cord and lifts the armature, A. To the poles, N, S, of the magnet are secured two small magnets, C, C, one end of the coil wire being connected to line and the other to a contact point, 6. The armature A is secured by a spring to an insulated point, P, from which a wire passes through the firing fuse in the ground mine to earth. The other end of the armature carries a contact point which, when the buoy is struck, engages with a contact point, b, which is connected to earth through the interposed resistance of a 1,000-ohm resistance coil.

Method Of Defending Harbor Channel With Submarine Mines And Batteries Of Rapid Fire And High Powered Guns.

Field of ground mines, showing submerged electric-contact-floating buoys attached.

Rapid-fire battery to prevent countermining.

Battery of 8 and 10-inch disappearing guns.

Firing station and range-finders.

Method Of Defending Harbor Channel With Submarine Mines And Batteries Of Rapid-Fire And High-Powered Guns.

Our second engraving shows the automatic indicator or shutter, which is placed in the firing station on shore.

Now let us follow more closely the operation of blowing up the hostile ship. The instant the vessel strikes the buoy, the suspended ball, B, swings to one side, draws aside the cord, pulls up armature A, into contact with b, and causes the signal-battery current to pass by way of the 1,000-ohm resistance-coil down through the ground fuse to earth. This current, is too weak to ignite the fuse. At the same time the armature a (in the firing station), is attracted to the magnets, 6, 6, and releases the pivoted shutter, 4, ringing the bell and throwing the signal battery line L into circuit with the line to the firing battery, F, B. The operator now places the plug, P, in place, and sends the whole force of the main current into the line, and as this has sufficient force to pass the resistance and ignite the fuse, the ground mine is instantly exploded. In the case of an automatic mine of the kind that is claimed to have sunk the "Petropavlovsk," the instant the floating sphere or case is struck by the ship, there is an explosion of the charge, which is carried in the floating case, if the water is very deep, or in the ground mine at the bottom if the water is sufficiently shallow to bring the mine within striking distance of the ship's bottom.

Ground Mine, Electric Contact, Buoy, And Shutter At Firing Station.

Ground Mine, Electric-Contact, Buoy, And Shutter At Firing Station.