y _mining_, as a military term, we understand the operations
resorted to for the demolition, with powder, of a military structure of
any description. The term _mine_ is applied both to the excavation
charged with powder for the purpose of producing an explosion, and to
the communications which lead to this excavation.

The place in which the charge of powder is lodged is called the
_chamber_, the communication by which this place is reached the
_gallery_, and the excavation made by the explosion is termed the
_crater_.

The form of the crater caused by an explosion in ordinary soils is
assumed to be a truncated cone, the diameter, _c d_, (Fig. 53,) of the
lower circle being one-half the diameter, _a b_, of the upper circle.
This form has never been ascertained to be exactly correct, but the
theoretical results deduced from a mathematical discussion of this
figure have been fully verified in practice. The radius, _p b_, of the
upper circle is termed the _crater radius_; the line _o p_, drawn from
the centre of the charge perpendicular to the surface where the
explosion takes place, is termed the _line of least resistance_; the
line _o b_, drawn from the centre of the powder to any point in the
circumference of the upper circle, is termed the _radius of explosion_.

When the crater radius is equal to the line of least resistance, the
mine is termed _common_; when this radius is greater than the line of
least resistance, the mine is termed _overcharged_; and when the radius
is less, _undercharged_. A mine of small dimensions, formed by sinking a
shaft in the ground, is termed a _fougasse_. The term _camouflet_ is
applied to a mine used to suffocate the enemy's miner, without producing
an explosion. Small mines made in rock or masonry, merely for the
purpose of excavation, without any considerable external explosion, are
called _blasts_.

From experiments made on common mines, whose line of least resistance
did not exceed fifteen feet, it has been ascertained that the tenacity
of the earth is completely destroyed around the crater to a distance
equal to the crater radius, and that empty galleries would be broken in
at once and a half that distance. It has also been proved by experiment,
that the crater radius in overcharged mines may be increased to six
times the line of least resistance, but not much beyond this; that
within this limit the diameter of the crater increases nearly in the
ratio of the square roots of the