676 PHILOSOPHICAL TRANSACTIONS. [aNNO 1742-3. 



124- ; for by comparing these experiments together, and making the necessary 

 allowances, it will be found, that the elasticity was nearly proportional to the 

 density in all that variety of densities. 



In this proposition, the analogy between the fluid produced by the explosion 

 of powder and common air, is established thus far, that they exert equal elasti- 

 cities in like circumstances; for this variation of the elasticity, in proportion to 

 the density, is a well-known property of common air. But other authors, who, 

 since the time of Mr. Boyle, have examined the factitious elastic fluids pro- 

 duced by burning, distillation, &c. have carried this analogy much further, and 

 have supposed these fluids to be real air, endued with all the properties of that 

 we breathe; particularly Dr. Hales, who has pursued this examination with the 

 greatest exactness, in a series of the best contrived processes, constantly affixes 

 the denomination of air to these factitious fluids, he having found that their 

 weight is the same with that of common air, and that they dilate with heat, 

 and contract with cold ; and that they vary their densities, under different de- 

 grees of impression, in the same proportion with common air; and from hence, 

 and other circumstances of agreement between them, he supposes them to be 

 of the same nature with air, and conceives them to be fitly designed by the 

 same name. 



But so perfect a congruity between these factitious fluids and air, is not 

 necessary for the purposes of this treatise. The fundamental positions of this 

 first chapter supposing no more, than that the elasticity of the fluid, produced 

 in the explosion of gunpowder, is always, caeteris paribus, as its density ; and 

 that the force of fired gunpowder is only the action of that fluid modified ac- 

 cording to this law. 



The law of the action of this fluid being determined, 2 methods offer them- 

 selves for investigating the absolute force of powder on the bodies it impels be- 

 fore it. The first by examining the quantity of this fluid produced by a given 

 quantity of powder, and thence finding its elasticity at the instant of the ex- 

 plosion : the other by determining the actual velocities communicated to bullets 

 by known charges, acting through barrels of different dimensions. The first is 

 the most easy and obvious, but the 2d the most accurate method ; and there- 

 fore the author has separately pursued each, and he has found, that their con- 

 currence has greatly exceeded his expectation, and thereby both of them receive 

 an additional confirmation. 



By the method described, it is collected, that the elasticity of the fluid pro- 

 duced from fired gunpowder, when contained in the space which was taken up 

 by the powder before the explosion, is about 1000 times greater than the 



