Page:Air Service Boys over the Rhine.djvu/99

Rh large, so as to get a big surface area for the gases of the burning powder to act upon, you get your shell too heavy to handle.

"Now of course the lighter a missile is, the farther it will go, in comparison to a heavy one with the same force behind it. But you can not get lightness and sufficient resistance to pressure without size, and here is where the sub-calibre comes in."

"In other words the Germans have been firing a shell within a shell," broke in another officer.

"Exactly," said Major de Trouville. "The Germans have evolved a big gun, that is big as regards length, to enable the missile they fire from it to gain enough impulse from the powder. But the missile would be too large to travel all the way to Paris. So they use two. The inner one is the one that really gets here and explodes."

"What becomes of the outer?" asked Jack.

"It is a sort of container, or collar, and falls off soon after the shell leaves the big gun. If you will imagine a sort of bomb shell being enclosed in an iron case, the whole being put in a gun and fired, you will better get the idea. The outer case is made in two or more pieces, and soon after it is shot out it falls away, leaving the smaller missile to travel on. But here