Unfortunately in most cases where a neutral ship is so sunk, the exploding mine automatically destroys all evidence of its own origin, and each belligerent promptly and positively declares that it must have been planted, if not deliberately set adrift, by the other side. The neutral is left to get what satisfaction he can out of the ruling of the last Hague Conference that all contact mines must be so constructed as to become harmless after breaking loose from their moorings. There is nothing mechanically difficult about installing such a safety device, and all the great powers now at war with each other solemnly pledged themselves to do so. But the temptation of perhaps destroying a hostile battleship as the _Hatsuse_ was destroyed, by a drifting mine, has apparently been too great.
Premature explosion of the mine during handling and planting, such as caused the destruction of the _Yenisei_ is, of course, carefully guarded against. One of the simplest and most effective safety devices is that used in the British navy, where the external parts of the exploding apparatus are sealed with a thick layer of sugar, which is dissolved by the sea-water after being submerged for a few minutes. By then the mine-laying vessel has had time to get safely out of the neighborhood.
Modern mines are of various shapes and sizes but are as a rule either spherical or shaped like a pear with the stem down. The anchor is a hollow, flat-bottomed cylinder, containing its own anchor cable wound on a windlass, and making a convenient base or stand for the explosive chamber or mine proper, so that the whole apparatus can be stood or trundled about the deck of a mine-layer like a barrel. Once placed in the water either by being dropped through the overhanging stern-ports of a large sea-going mine-planter like the U.S.S. _San Francisco_, or lowered over the side of a smaller craft by a derrick boom, the weight of its anchor causes the mine to assume an upright position. This releases a small weight or plummet at the end of a short line attached to a spring that keeps the windlass inside the anchor from revolving. When the plummet has sunk to the end of its cord, its weight pulls down the spring, and the windlass begins to revolve and unreel the cable, the end of which is, of course, made fast to the bottom of the mine. This causes the anchor, which has been held up by the buoyancy of the mine, to sink, and follows the plummet till the latter touches the bottom. Freed of the plummet’s weight, the spring now flies up and stops the windlass. But the hollow anchor is now filled with water, whose additional weight drags the mine under. When the anchor rests on the bottom, the mine will be at the same distance beneath the surface of the water as the anchor had to sink after the windlass stopped, or the length of the plummet’s line. By regulating that, a mine can be made automatically to set itself at any desired depth.