ON THE TIME TAKEN TO DRAW A BALL TO THE GROUND BY THE FORCE OF GRAVITY.
If fired with axis parallel to the ground.
1st Case. Supposing a ball to be fired when the axis of the piece is parallel to the ground and 16 feet above it, then the projectile will strike the earth in the same length of time that it would have done, had it been rolled out of the muzzle, quite irrespective of the velocity with which it may have been propelled, or the consequent extent of range; that is to say the ball will have reached the point B., ([plate 22], fig. 1.), in the same length of time that it would require to fall from the muzzle A., to the earth C.; i. e., in one second.
2nd Case. Were three guns to be fired at the same instant, with their three axes parallel to the horizon as before, and loaded respectively with 1⁄2 drm., 1 drm., and 11⁄2 drm. of powder of the same strength, then, although the three initial velocities and three ranges would consequently all be different, yet the three balls would strike the ground at the same time, i. e. at the points B. B. B. in one second. ([Plate 22], fig. 2.)
If axis at an angle to the ground.
3rd Case. When a ball is fired at an angle of elevation it will reach the earth in the same length of time which it would occupy in falling the length of the tangent of the angle of projection; hence supposing F. G. ([plate 22], fig. 3.) to be 16 feet, the ball would reach the point G. in one second, irrespective of the distance from D. to G.
ATMOSPHERE.
Let us now take into our consideration the course of a projectile while under the influence of three forces, viz., powder, gravity, and air.
Why named.