32© Mr. Thompson’s Experiments 
X 
the theorem — + b = z ; and the a&ual recoil is marked, 
s/ a + X s 
upon the ordinates to this curve by large round dots, which in 
all the experiments, except the 86th and 8yth, very nearly 
coincide with the curve.. 
In the fig 18. the numbers upon the line- AH, 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 reeoil when 
the given chargp 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 
intirely the lofs of force by the efcape of the elaftic fluid 
through the vent and by the windage, I fhall leave it to ma- 
thematicians. to determine from thefe data the properties of 
that fluid.. 
But, before I take my leave of this fubjed,.. I would. juft ob- 
ferve, that Mr. robins is not only miftaken in the principle he 
affumes, refpeding the relation of the elafticity of the fluid 
generated from gun-powder to its denfity, or rather the law of 
its aclion 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 924 experi- 
ment, that its force is at lead: j 308 times greater than the 
mean 
