76 'Experiments upon Gunpowder. 



able to appreciate, the effect of each varying circumstance, 

 under which an experiment can be made. But when, 

 concluding too hastily from the result of a partial ex- 

 periment, we suppose, with Mr. Robins, that, because 

 the sum total of the action or pressure of the elastic 

 fluid upon the bullet, during the time of its passage 

 through the bore, happens to be the same when bullets 

 of different weights are made use of (which collective 

 pressure is in all cases proportional to, and is accurately 

 measured by, the velocity, or rather motion, communi- 

 cated to the bullet), that, therefore, the pressure in any 

 given part is always exactly the same when the quantity 

 of powder is the same with which the piece is fired ; 

 and from thence endeavour to prove that the inflam- 

 mation of gunpowder is instantaneous, or that the 

 whole charge is, in all cases, inflamed and " converted 

 into an elastic fluid before the bullet is sensibly moved 

 from its place," such reasonings and conclusions may 

 lead to very dangerous errors. 



It is undoubtedly true, that if the principles assumed 

 by Mr. Robins, with respect to the manner in which 

 gunpowder takes fire, and the relation of the elasticity 

 of the generated fluid to its density, or the intensity of 

 its pressure upon the bullet, as it expands in the barrel, 

 were just, and if the loss of force by the vent and by 

 windage were%in all cases inconsiderable, or if it were 

 prevented, the deductions from the theory respecting the 

 velocities of bullets of different weights would always 

 hold good. But if, on the contrary, it should be found 

 upon making the experiments carefully, and in such a 

 manner as entirely to prevent inaccuracies arising from 

 adventitious circumstances, that the velocities observe a 

 law different from that which the theory supposes, we 



