220 Mr. -Thompson's Experiments 
the theorem — ==• + i — z ; and the a&ual recoil is marked 
s/ CL + 
upon the ordinates to this curve by large round dots, which in 
all the experiments, except the S6th and 87th, very nearly 
coincide with the curve. 
In the fig 18. the numbers upon the line AB, taken fiom A, 
denote the different charges of powder ufed in the courfe of 
the experiments, while the ordinates to the curve cd , exprefs 
the velocities of the bullets, with the vent at o. The lines 
drawn perpendicular from the line AB to the line ef, repre- 
fent the recoil with the feveral charges of powder, and a leaden 
bullet ; and the portion of thofe lines that is comprehended 
between the line AB and the line gh , denotes the recoil when 
the given charge was fired without any bullet. 
Having now fhewn by experiment the relation of the veloci- 
ties of bullets to their weights, when care is taken to prevent 
mtirely. the lofs of force by the efcape of the elaftic fluid 
through the vent and by the windage, I (hall leave it to mar 
thematicians to determine from thefe data the properties of 
that fluid. 
But,, before I take my leave of this fubject,. I would juft ob- 
ferve,; that Mr. robins is not only miftaken in the principle he 
afliimes, refpefting the relation of the elafticity of the fluid 
generated from gun-powder to its denfity, or rather the law of 
its a&ioii upon the bullet as it expands in the bore; but his 
determination of the force of gun-powder is alfo erroneous,, 
even upon his own principles : for he determines its force to be 
1000 times greater than the mean preflure of the atmo- 
fphere; whereas, it appears, from the refult of the 9 2d experi- 
ment, that its force is at leaft 1308 times greater than the 
mean 
