Page:Our big guns.djvu/14

( 8 ) If solid shot were used, you will see the weight was incapable of adjustment, being determined by that of a sphere of cast iron of a diameter slightly less than that of the bore, the difference being to allow the "windage" that the irregularity of the surface of the projectile rendered necessary.

The charge of powder was commonly about one-third of the weight of the ball.

To come to more modern guns of the same construction; take as an example the 68-pounder, the heaviest gun it was thought possible, at the date of its use, to mount on shipboard; this was an 8-inch gun, the length of its bore was 9 feet 6 inches or 14¼ calibres, the weight of the gun was 95 cwt., the charge of powder was 16 lbs., and the velocity of the 68 lb. ball on leaving the muzzle was about 1600 feet per second.

It will be seen that as the bore of the gun and the weight of the ball increased, it was deemed expedient not to retain the relative proportion of powder to ball, viz. one-third, that had prevailed in the 32-pounder, but to reduce it to a little below one-fourth. Neither was it found that the same length in calibres could be given, and these were reduced from the 17 in the 32-pounder to 14¼ in the 68-pounder.

It will be clear to you, that as a shot passes through the air its velocity must gradually diminish, and it will also be clear to you that as the velocity diminishes, the stored up energy in the shot, or the power to do work, upon that which it is to strike, also diminishes. This it does indeed in a ratio far exceeding that of the mere reduction in velocity, viz. in the ratio of the squares, so that a shot that is still travelling, at half the pace of the muzzle velocity, contains only one-fourth of the energy that was stored up in it as it left the mouth of the gun, and possesses therefore only one-fourth of the destructive power. But there is another reason why the retention as far as possible of the muzzle velocity is of importance, which is, that it enables a longer range to be obtained, and shorter ranges to be accomplished with less elevation of the gun—a great advantage, as the following considerations will show. If the velocity were