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Rh very close accord between the figures applying to the gun and those which obtain in the gas-engine. In all such matters as efficiency, heat lost to barrel (cylinder walls), and heat remaining in gases ; the agreement is far closer than one would have ventured to expect in view of the great disparity of the conditions.

§ 59. Energy Available and Otherwise. It has already been pointed out that under the conditions of attack on aircraft there is very little possibility of utilising the whole of the energy of the bullet on impact. Unless the motor mechanism, or the pilot or gunner, be hit, the character of the structure employed in aircraft is such that the bullet or projectile will pass through with a comparatively insignificant loss of energy and will do little or no damage. With the ordinary military bullet, and more particularly with the spitzer model, nothing less than encounter with a heavy metal part will cause it to break up. Any non-metallic structural material, such as timber, is bored cleanly through, and if initially designed with a reasonable margin of safety, the resulting injury to it is negligible. The position is similar to that which existed, before the adoption of explosive shell, in the attack on the wooden ship by the artillery or cannon of a century ago. At close quarters the cannon ball would go clean through, often with comparatively little injury. It is said that Napoleon, observing this to be the case, himself expressed the opinion that explosive shell (a then well-known expedient in siege operations) could be adopted generally in naval warfare with advantage. The situation is considerably more acute in the case of the attack on aircraft by rifle-fire, and so we are led to consider the possibilities of the ex- plosive or expanding bullet, ignoring, for the purpose of discussion, the existence of the Declaration of St. Petersburg.