io8 Experiments to determine 



wards found abundant reason to conclude, was the. real 

 cause of these variations, and of all the principal diffi- 

 culties which attended the ascertaining the force of fired 

 gunpowder by the methods I had hitherto pursued. 



It has generally been believed, after Mr. Robins, that 

 the force of fired gunpowder consists in the action of a 

 permanently elastic fluid, similar in many respects to 

 common atmospheric air ; which, being generated from 

 the powder in combustion, in great abundance, and being 

 moreover in a very compressed state, and its elasticity 

 being much augmented by the heat (which is likewise 

 generated in the combustion), it escapes with great vio- 

 lence by every avenue, and produces that loud report, 

 and all those terrible effects, which attend the explosio.n 

 of gunpowder. 



But though this theory is very plausible, and seems 

 upon a cursory view of the subject to account in a satis- 

 factory manner for all the phaenomena, yet a more 

 careful examination will shew it to be defective. 

 There is no doubt but the permanently elastic fluids, 

 generated in the combustion of gunpowder, assist in 

 producing those effects which result from its explosion ; 

 but it will be found, I believe, upon ascertaining the 

 real expansive force of fired gunpowder, that this cause 

 alone is quite inadequate to the effects actually pro- 

 duced ; and that, therefore, the agency of some other 

 power must necessarily be called in to its assistance. 



Mr. Robins has shewn that if all the permanently 

 elastic fluid generated in the combustion of gunpowder 

 be compressed in the space originally occupied by the 

 powder, and if this fluid, so compressed, be supposed to 

 be heated to the intense heat of red-hot iron, its elastic 

 force in that case will be looo times greater than the 



