Page:Popular Science Monthly Volume 92.djvu/257

 Firing a Cannon From a Cannon

An inventor's ingenious plan to bring down aircraft flying at great heights

��ONCE upon a time, so an old fairy tale runs, a lunatic wanted to bom- bard the moon. He invented a shell that was in itself a cannon. During its flight, this projectile- cannon would discharge an- other shell, which was also a cannon. And so by firing successive cannons within cannons the lunatic thought that he might -cover the space of 260,000 miles that sep- arates us from our satellite.

Now that cannon must be fired at elusive aircraft, this ancient idea has been revived in earnest. Airplanes must be fired at point blank, there is neither opportunity nor time to figure out the exact range. On the other hand, the explosion of the shrap- nel-shell is not so easily timed. The hail of bullets that follows the bursting of shrapnel meets so much more air re- sistance than the shell itself that not only is the scattering effect too great, but the striking force is too small. If by any chance the explosion be timed too early, the scattering effect is not sufficient and the airplane is not winged as a shot-gun wings a snipe or a quail.

Andrew W. Gra- harn meets this diffi- culty by inventing a shell that is not merely an envelope to hold bullets together for a certain distance, as in

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����Firing pin Cartridc^e timing disk \ Coi

���Rifled bai-re

��Revolving sleeve

The ordinary fuse used in shrapnel sets off the charges of the rifled passages of the shell

��shrapnel, but which, like that in the fairy- tale, is a gun in itself, and a very powerful Gatling gun at that.

The projec- tile is pierced with a dozen or so of rifled chan- nels, each constituting a barrel loaded with a regulation rifle cartridge. The inventor has provided a lock and firing pin for each hole and a clock-work mechanismto fire simulta- neously series of barrels or holes. This mechanism seems a need- 1 e s s and hardly feasi- ble complica- tion. Such is the concus- sion in a shell when it is fired from a gun tnat the shrapnel balls must be cemented together. How will clock-work endure a shock that even solid balls cannot withstand? The fuse used in shrapnel, a marvel of accurate mechanism, adapts itself to setting off the charges of the rifled passages of Mr. Graham's shell. By thus discarding the clock mechanism, the barrels or rifled holes can be made longer, which means greater accuracy of fire.

��The Gun Within a Gun

A shell like that which Mr. Graham has conceived can be timed to dis- charge its bullets efficiently, far from its target, unlike shrapnel. The bul- lets do not lose in velocity, thanks to their elongated form and their rotation. Their velocity is the sum of the shell's velocity and their own. Were it not for the centrifugal action of the shell, they would not scatter. The firing can be timed so that at least one volley will scatter properly.

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