The following rules are given by Vauban for fougasses, or small mines, having the diameter of the excavation equal to double the line of least resistance. The side of the chamber must be exactly a sixth part of the depth of the shaft. The side of the box to hold the powder exactly a ninth part of the depth of the shaft.
These remarks respecting mines are principally extracted from the General Essay on Fortification before mentioned, written in French and published at Berlin, 1799.
Counter-Mines, are those made by the besieged, whereas mines are generally made by the besiegers. Both mines and counter-mines are made in the same manner, and for the like purposes, viz. to blow up their enemies and their works; only the principal galleries and mines of the besieged, are usually made before the town is besieged, and frequently at the same time the fortification is built, to save expence.
Eventer la Mine, Fr. to spring a mine. When used figuratively, this expression signifies to discover a plot, or make it known. It is likewise used to express the failure of any expedition or undertaking.
Definitions of Mines. A mine is a subterraneous cavity made according to the rules of art, in which a certain quantity of powder is lodged, which by its explosion blows up the earth above it.
It has been found by experiments, that the figure produced by the explosion is a paraboloid, and that the centre of the powder, or charge, occupies the focus.
The place where the powder is lodged is called the chamber of the mine, or fourneau.
The passage leading to the powder is called the gallery.
The line drawn from the centre of the chamber, perpendicular to the nearest surface of the ground, is called the line of least resistance.
The pit or hole, made by springing the mine, is called the excavation.