upon Gun-powder , &c. 267 
Now the effort of any given charge of powder upon the gun 
is very nearly the fame, whether it be fired with a bullet or 
without ; but the velocity with which the generated elaftic 
fluid makes its efcape, is much greater when the powder is 
fired alone, than when it is made to impel one or more bullets ; 
the heat ought therefore to be greater in the former cafe than 
in the latter, as I found by experiment. 
But to make this matter {till plainer, we will fuppofe any 
given quantity of powder to be confined in a fpace that is juflf 
capable of containing it, and that in this fituation it is by any 
means fet on fire. Let us fuppofe this fpace to be the chamber 
of a piece of ordnance of any kind, and that a bullet, or any 
other folid body, isfo firmly fixed in the bore immediately upon 
the charge, that the whole effort of the powder {hall not be able 
to remove it. As the powder goes on to be inflamed, and the 
elaftic fluid is generated, the preffure upon the infide of the 
chamber will be increafed, till at length ali the pow- 
der being burnt, the {train upon the metal will be at its 
greateft height, and in this fituation things- will remain, the 
cohefion or elafticity of the particles of metal counterbalancing 
the preffure of. the fluid. 
Under thefe circumftances very little heat would be gene- 
rated ; for the continued effort of the elaftic fluid would ap- 
proach to the nature of the preffure of a weight; and that 
concuflion, vibration, and fri&ion, among the particles of the 
metal, which in the collifion of elaftic bodies is the caufe of 
the heat that is produced, would Tcarcely take effect. 
But inftead of being firmly fixed in its place, let the bullet, 
now be moveable, but let it give way. with great difficulty, and . 
by flow degrees. In this cafe, the elaftic fluid will be gene- - 
rated as before, and will exert its whole force upon the chamber 
of; 
