The excavation for receiving the _charge_ is called the _chamber_. The approaches leading to the chamber when horizontal or somewhat inclined are called _galleries_, and when vertical are known as _shafts_. When very steep they are sometimes called _slopes_. The charge, chamber, and approaches taken together constitute a _mine_. The pit formed by the explosion is called the _crater_. When the ground is homogeneous and its surface horizontal, the intersection of its surface by the crater is approximately a circle, the radius of which is called the _crater radius_, _AB_, Pl. XI, Fig. 1. The right line joining the centre of the charge with the nearest point of the surface toward which the explosion will take place, generally the surface of the ground, is called the _line of least resistance_ (written generally L. L. R.), _C B_, Pl. XI, Fig. 1. A right line from the centre of the charge to the edge of the crater is called the _radius of explosion_, _C D_, Pl. XI, Fig. 1. The distance from the centre of the charge at which an ordinary mining gallery will be broken in by the explosion is called the _radius of rupture_, _C L_, Pl. XI, Fig. 3. The radius of rupture varies in length with its inclination to the horizontal. Craters whose _diameters_ are once, twice, etc., their lines of least resistance are called _one-lined_, _two-lined_, etc., craters. Mines in which the L. L. R. is equal to the _crater radius_ are called _common mines_. (Their craters are _two-lined_.) Those in which the crater radius exceeds the L. L. R. are called _overcharged mines_ or _globes of compression_; when it is less, they are _undercharged mines_; and when the charge is so small that no exterior crater is formed, they are known as _camouflets_. =2.= In the explosion of military mines on land it may safely be assumed that the circumstances of combustion of the charge when fired are such that the energy developed is directly proportional to the charge. A portion of this energy is generally lost by the escape of the compressed gases into the air, by the heat given up to the surrounding media, and by the transmission of earth-waves or shock; the remainder and greater part, however, is expended in rupturing the case containing the charge, compressing the soil in its immediate vicinity, separating that lifted up from that forming the sides of the crater, breaking up the portion thrown out into large or small fragments, projecting them to a greater or less distance, and disintegrating the soil around the crater to a distance which varies with the soil and with the quantity and character of the explosive used. As the proportional part of the energy expended in each of the effects above named cannot be determined in any particular case, and as each case differs in some respect from every other, it is manifestly impossible to express in any mathematical formula a rule for determining the exact amount of explosive required for any particular mine.