Page:Popular Science Monthly Volume 13.djvu/290

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the vibrations of the gun, which, to some extent, rings like a bell. This latter, I apprehend, will disappear at considerable distances." The result of subsequent trial, as reported by General Campbell, is,

PSM V13 D290 Breech loading fog signal cannon.jpg
Fig. 1.—Breech-loading Fog-Signal Gun, with Bell-Mouth, proposed by Major Maitland, R.A., Assistant Superintendent.

that "the sonorous qualities of bronze are greatly superior to those of cast-iron at short distances, but that the advantage lies with the baser metal at long ranges."[1]

Coincident with these early trials of guns at Woolwich, gun-cotton was thought of as a probably effective sound-producer. Theoretic considerations caused me to fix my attention persistently on this substance; for the remarkable experiments of Mr. Abel, whereby its rapidity of combustion and violently explosive energy are demonstrated, seemed to single it out as a substance eminently calculated to fulfill the conditions necessary to the production of an intense wave of sound. What those conditions are we shall now more particularly inquire, calling to our aid a brief but very remarkable paper, published by Prof. Stokes in the Philosophical Magazine for 1868.

The explosive force of gunpowder is known to depend on the sudden conversion of a solid body into an intensely heated gas. The work which the artillerist requires the expanding gas to perform is the displacement of the projectile. Such, however, is not the work that we want our gunpowder to perform. We wish it to transmute its energy not into the mere mechanical translation of the shot, but into vibratory motion. We want pulses to be formed which shall propagate themselves to vast distances through the atmosphere, and this requires a certain choice and management of the explosive material.

  1. General Campbell assigns a true cause for this difference. The ring of the bronze gun represents so much energy withdrawn from the explosive force of the gunpowder. Further experiments would, however, be needed to place the superiority of the cast-iron gun at a distance beyond question.