CC 42000 465• " CC " 2500 "' " 367 " Action and reaction being always equal and in opposite directions, the explosion of the gunpowder acts with equal force upon the ball and upon the cannon from which it is discharged, the former demonstrating this in its range, and the latter by its recoil. This recoil has to be guarded against as much as possible, either by the weight of the gun itself, or by its secure attachment to a ponderous carriage. The momentum of the recoil, being the product of the shot's weight, and the velocity, is readily calculated. The common charge of a 24-pounder gun, being one-third the weight of the shot, or 8 lbs., the momentum of both shot and gull, will be 1600 (the initial velocity) X 24 = 38,400, which, divided by 5,600, or the gun's weight in pounds, gives about 7 ft. as the velocity per second; if the gnu is attached to a carriage, the weight of the carriage must be added to that of the gun for a divisor.
The following table exhibits the effects of varying charge and elevation on different kinds of guns. The line of sight of a gun is an imaginary line drawn through the back sight on the breech and the fore-sight, a notch in the muzzlering. or on the first re-in fofce. The fore-sight is immovable, but the back-sight is so constructed that the notch shall be at a greater or less height above the axis of the gun. When the line of sight
is parallel to the axis and horizontal, the discharge is " point-blank ;" but when the back-sight is raised, the direction of the axis of the gun will be to a point more elevated than that to which the line of sight is directed. Consequently, by raising the back sight, a greater elevation, and, ordinarily, a greater rouge, is given to the piece. In regard to point-blank discharge, Tartaglia established the fundamental proposition that the time occupied by the ball in describing the whole trajectory or path is the same as it would require to fall by gravity from the muzzle to the ground.
As regards penetration, it was found by experiments against a martello tower at East bourne, with a range of 1832 yards. that solid shot. from the 40-pounder Armstrong pen• etrated intogood masonry from 47 to 65 in., and from an 80-pounder Armstrong 51 to 90 inches. or other particulars relative to the art of gunnery, the reader is referred to LOADING, PROJECTILES, WINDAGE, etc. The important point of the rotation of a ball or bolt will be considered under RIFLED FIRE: Anus.