VOL. LXXXVII.] PHILOSOPHICAL TRANSACTIONS. \Qq 



here found indicating its value, as determined by computation-. It is therefore 

 tHt.t = 6.3744 for the value of this co-efficient, and this multiplied into the 

 number 147Q.5, gives 9431 for the value of y in atmospheres. 



Again, the density being supposed = 1000 (or, that the charge of powder com- 

 pletely fills the cavity in which it is confined), in that case it will be 1000'+°-4 = y 

 = 1584g, and this number being turned into atmospheres by being multiplied by 

 the co-efficient above found (= 6.3744), gives 101021 atmospheres for the mea- 

 sure of the initial force of the elastic fluid generated in the combustion of gun- 

 powder. Enormous as this force appears, I do not think it over-rated ; for nothing 

 much short of such an inconceivable force can, in my opinion, ever explain in a 

 satisfactory manner the bursting of the barrel so often mentioned ; and to this we 

 may add, that, as in 7 different experiments, all made with charges of 1 2 grs. of 

 powder, there were no less than 5 in which the weight was raised with a report, and 

 as the same weight was moved in 3 different experiments in which the charge con- 

 sisted of less than 12 grs., there does not appear to be any reason whatever for 

 doubt with regard to the principal fact on which the above computation is 

 founded.* 



There is an objection however, that may be made to these decisions respecting 

 the force of gunpowder, which, on the first view, appears of considerable import- 

 ance ; but on a more careful examination it will be found to have no weight. If 

 the force of fired gunpowder is so very great, how does it happen that fire-arms and 

 artillery of all kinds, which certainly are not calculated to withstand so enormous a 

 force, are not always burst when they are used ? I might answer this question by 

 another, by asking how it happened that the barrel used in my experiments, and 

 which was more than 10 times stronger in proportion to the size of its bore than 

 ever a piece of ordnance was formed, could be burst by the force of gunpowder, if 

 its force is not in fact much greater than it has ever been supposed to be ? But it is 

 not necessary to have recourse to such a shift to get out of this difficulty : there is 

 nothing more to do than to show, which may easily be done, that the combustion 

 of gunpowder is less rapid than it has hitherto been supposed to be, and the objec- 

 tion in question falls to the ground. Mr. Robins's theory supposes that all the 

 powder of which a charge consists is not only set on fire, but that it is actually con- 

 sumed and " converted into an elastic fluid before the bullet is sensibly moved from 

 its place." I have already, in the former part of this paper, offered several reasons 

 which appeared to me to prove that, though the inflammation of gunpowder is very 

 rapid, yet the progress of the combustion is by no means so instantaneous as has 

 been imagined. I shall now give an account of some experiments which put that 

 matter out of all doubt. 



* Reasons, however, have been given in the foregoing notes, not only for doubt of such computations, 

 but for proof of the fallacy of the principles on which they are made. One might have expected that th« 

 enormous number of 1 00,000 atmospheres might have staggered any philosopher ! 



VOL. XVIII. Z 



