Slow Powders are those which are not entirely burned when the projectile leaves the muzzle.
Velocity of Emission is the ratio of the amount of a unit weight of powder, burned in air in a small increment of time, to the time itself.
The Sectional Density is equal to the weight of the projectile divided by the square of its diameter.
Spherical Density is the ratio of the weight of the projectile to that of a sphere whose radius is equal to that of the right section of the projectile.
Similar Guns.—Two guns are similar when all their homologous lineal dimensions are proportional to their calibre.
Similarly Loaded.—When the weight of charge and projectile are proportional to the cube of the calibre, and the grains of powder are alike in form and composition, with dimensions proportional to the calibre.
EXTERIOR BALLISTICS.
Exterior Ballistics treats of the motion of a projectile in air after it has left the piece.
Trajectory.—The curve described by the centre of gravity of the projectile during its passage through the air. (Figs. 102 and 103.)