-2 f Mr. Thompson’s Experiments 
puted from the diameter of the bore of the piece, and the fpe- 
cific gravity of the powder that was made ufe of. 
N. B. By an experiment 1 ihali give an account of hereafter, 
I found the fpecific gravity of this powder fhaken well together 
to be to that of rain water as 0,937 t0 I 5°°°* 
In the experiment N° 30. the pow- 
der was put into a cartridge fo much 
fmaller than the bore of the piece, that 
the charge, inftead of occupying 1 ,45 
inches, extended 3,2 inches. By this 
difpofition of the powder, its adtion 
upon the bullet appears to have been 
very much diminifhed. 
Of the ejfeffi that the heat which pieces acquire in firing produces 
upon the force of powder . 
It is very probable, that the excefs of the velocity of the 
bullet in the fecond experiment over that of the firft was occa- 
honed more by the heat the barrel had acquired in the hr ft 
experiment than by the pofition of the vent, or any other 
circumftance ; for I have face found, upon repeated trials, that 
the force of any given charge of powder is conhderably greater 
, when it is fired in a piece that has been previoufly heated by 
firing, or by any other means, than when the piece has not been 
heated. Every body that is acquainted with artillery knows, 
that the recoil of great guns is much more violent after the 
fecond or third difcharge than it is at firft ; and on fhip-board, 
where 
WeightjHeight of the charge, 
of the — i — 
powder. 
Meafured. 
Computed. 
Grs. 
Inches. 
Inches. 
104 
>9 
0,8957 
145 
1,2490 
165 
i >45 
I > 4 21 1 
208 
1,8 
Ij 79 t 4 
218 
1,9 
i , 8 775 
290 
2,6 
2,4980 
31° 
2,7 
2,6700 
33 ° 
2,9 
2,8422 
416 
3 > 6 
3G 828 
437 i 1 
3>9 
3,7680 
