EXTERIOR BALLISTICS. In exterior ballistics, we determine the path of the projectile, knowing its shape, calibre, weight, its initial velocity of translation and rotation, the resistance it meets from the air, and the action of gravity. To this branch of the science the tions would apply: The Trajectory is the curve described by a point on the axis of a projectile in its passage through the air. It is divided into ascending and descending branches, the highest point of flight being called the summit.
By Rigidity 'of Trajectory is meant the im portant principle, proven analytically, that the whole trajectory, with its chord, may be re volved a certain distance about a horizontal axis passing through the centre of the muzzle, without changing the relations between the tra jectory and its chord.
The Line of Sight is the line passing through the sights of the piece and the point aimed at.
The Line of Departure is the prolongation of the axis of the bore at the instant the projectile leaves the gun; or it is the tangent to the tra jectory at the muzzle.
The Plane of Sight, sometimes called the plane of fire, is the vertical plane containing the line of sight.
The Plane of Departure is the vertical plane containing the line of departure.
The Angle of Departure is the angle made by the line of departure with the horizontal plane.
The Angle of Elevation is the angle made by the axis of the bore with the horizontal plane when the piece is laid.
The Jump is the difference between the angle of elevation and the angle of departure.
Drift is the departure of the projectile from the plane of fire due to the resistance of the air and the rotation of the projectile.
Muzzle Velocity is the velocity of the pro jectile on leaving the piece.
Remaining Velocity is the velocity at a given point of the trajectory.
Striking Velocity is the remaining velocity at the target.
The Horizontal Range is the horizontal dis tance from the muzzle of the gun to that point of the descending branch of the trajectory (point of fall) which is at the level of the gun. Ordinarily the term range means the distance between the gun and the target.
The Angle of Fall is the angle that the tangent to the trajectory at the point of fall makes with the horizontal plane passing through the muzzle.
The Striking Angle is the angle made by the tangent with the horizontal plane at the strik ing-point.
The Dangerous Space is the horizontal dis tance over which an object of a given height will be struck.
Direct Fire is with high velocities and angles of elevation not exceeding about 20 degrees.
Furred Fire is with low velocities and angles of elevation not exceeding about 20 degrees.
High Angle Fire is when the angle of eleva tion exceeds 20 degrees.
Indirect Fire is when the target is invisible from the firing-point.