258 FRAGMENTS OF SCIENCE. 



Coincident with these trials of guns at Woolwich, 

 gun-cotton was thought of as a probably effective 

 sound-producer. From the first, indeed, theoretic con- 

 siderations caused me to fix my attention persistently 

 on this substance; for the remarkable experiments of 

 Mr. Abel, whereby its rapidity of combustion and vio- 

 lently explosive energy are demonstrated, seemed to 

 single it out as a substance eminently calculated to ful- 

 fil the conditions necessary to the production of an 

 intense wave of sound. What those conditions are we 

 shall now more particularly enquire, calling to our 

 aid a brief but very remarkable paper, published by 

 Professor Stokes in the ' Philosophical Magazine ' for 

 1868. 



The explosive force of gunpowder is known to de- 

 pend on the sudden conversion of a solid body into an 

 intensely heated gas. Now the work which the artil- 

 lerist requires the expanding gas to perform is the dis- 

 placement of the projectile, besides which it has to dis- 

 place the air in front of the projectile, which is backed 

 by the- whole pressure of the atmosphere. Such, how- 

 ever, is not the work that we want our gunpowder to 

 perform. We wish to transmute its energy not into the 

 mere mechanical translation of either shot or air, 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. 



A sound-wave consists essentially of two parts a 

 condensation and a rarefaction. Now air is a very 

 mobile fluid, and if the shock imparted to it lacks due 

 promptness, the wave is not produced. Consider the 



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. 



