VOL. LXXXVII.] PHILOSOPHICAL TRANSACTIONS. I47 



also that its force consists principally in the temporary action of a fluid not per- 

 manently elastic, and consequently that all the theories hitherto proposed for the 

 elucidation of this subject, must be essentially erroneous. 



It would take up too much time, and draw out this paper to too great a length, 

 to give an account in detail of all the experiments, and of the various observations 

 I have had opportunities of making from time to time, relative to this subject. I 

 shall therefore only observe at present, that the result of all my inquiries tended to 

 confirm me more and more in the opinion, that the theory generally adopted relative 

 to the explosion of gunpowder was extremely erroneous, and that its force is in fact 

 much greater than is generally imagined. That the position of Mr. Robins, which 

 supposes the inflammation and combustion of gunpowder to be so instantaneous 

 " that the whole of a charge of a piece of ordnance is actually inflamed and con- 

 verted into an elastic vapour before the bullet is sensibly moved from its place," is 

 very far from being true; and that the ratio of the elasticity of the generated fluid, 

 to its density, or to the space it occupies as it expands, is very different from that 

 assumed by Mr. Robins. The rules laid down by Mr. Robins for computing the 

 velocities of bullets from their weight, the known dimensions of the gun, and the 

 quantities of powder used for the charge, may, and certainly do, very often give 

 the velocities very near the truth ; but this is no proof that the principles on which 

 these computations are made are just; for it may easily happen, that a complication 

 of erroneous suppositions may be so balanced, that the result of a calculation 

 founded on them may yet be very near the truth ; and this is never so likely to 

 happen as when, from known effects, the action of the powers which produce 

 them are computed. For it is not in general very difficult to assume such prin- 

 ciples as, when taken together, may in the most common known cases answer 

 completely all the conditions required. But in such cases, if the truth be dis- 

 covered with regard to any one of the assumed principles, and it be substituted in- 

 stead of the erroneous supposition, the fallacy of the. whole hypothesis will imme- 



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diately become evident. 



It may perhaps with reason be asked, what the circumstances were which at- 

 tended former experiments, which could justify so important a conclusion as that 

 of the fallacy of the commonly received theory relative to that subject. To this I 

 answer briefly, that in regard to the supposed instantaneous inflammation of the 

 powder, on which the whole fabric of this theory is built, or rather of all the com- 

 putations which are grounded on it, a careful attention to the phenomena which 

 take place on firing off* cannon led me to suspect, or rather confirmed me in my 

 former suspicions, that however rapid the inflammation of gunpowder may be, its 

 total combustion is by no means so sudden as this theory supposes. When a heavy 

 cannon is fired in the common way, that is, when the vent is filled with loose 

 powder, and the piece is fired off with a match, the time employed in the passage 

 of the inflammation through the vent into the chamber of the piece is perfectly 

 sensible, and this time is evidently shorter after the piece has been heated by re- 



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