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 ufc of. 
N. B. By an experiment I fhallgivean account of hereafter, 
I found the fpeeific gravity of this powder fhaken well together 
to he to that of rain water as 0,937 is to 1,000. 
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 action 
upon the bullet appears to have been 
very much diminilhed. 
Of the effeB 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- 
lioned more by the heat the barrel had acquired in the firft 
experiment than by the pofition of the vent, or any other 
circumftance ; for I have fmce found, upon repeated trials, that 
the force of any given charge of powder is confiderably 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 
heatec}. 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 ftiip-board, 
where 
; Weight Height of the charge. 
of the 
powder. 
j 
iMeafured. 
Computed. 
Grs. ;j 
Inches. 
Inches. 
,* 94 * l 
0 >9 
0,8957 
1,2490 
165 < 
*>45 
1,4211 
208 
jA 
*> 79*4 
218 
*>9 
1.8775 
290 
2,6 
2,4980 
31° 
2,7 
2,6700 
33 ° 
2>9 
2,8422 
416 
. 3 > 6 
3 ’ 9 V 
3^5828 
437 i 
3 7680 
