upon Gun-powder, &c. 313 
©ut leflening its elaftic force ? It would certainly aft upon very 
light bullets with greater force ; but when heavy ones came to 
be made ufe of, there is reafon to think, that, except extraor- 
dinary precaution was taken to prevent it, the greateft part of 
the force would be loft by the vent and by windage. 
The velocity with- which elaftic fluids rufh into a void fpace is 
as the elafticity of the fluid: directly, and inverfely as its den- 
fity ; if, therefore, the denfity of the fluid generated from 
powder was four times lefs than it is, its elafticity remaining 
the fame, it would iflue out at the vent, and efcape by the fide 
of the bullet in the bore, with nearly four times as great a 
velocity as it does at prefen t ; but we know from experiment 
that the lofe of force on thofe accounts is- now very confi- 
derable. 
in the experiments N° 76. and 77. when the piece was fired ! 
with 145 grains of powder, the velocity of the bullets at a 
medium was 1040 feet in a fecond ; j but in the 88th and 89th 
'experiments, when the bullets were even heavier, and the 
piece was fired with the fame quantity of powder, the mean 
velocity was 1232 feet in a fecond. The difference —1 92 
feet in a fecond, anfwers to-a difference of force greater in the 
left experiments than in the firft in the proportion of 14 to 10. 
I know of no; way to account for this- difference, but by fup- 
poling that it was owing intirely to the efcape of the elaftic 
fluid by the vent, and by windage, in thofe experiments where 
the vent was open, and the bullets were put naked into the 
piece* 
An elaftic bow, made of very light wood, will throw an 
arrow,, and efpecially a light one, with greater velocity than a 
bow of fteel of the fame degree of ftiffnefs : but, for praftice,- 
I think it is plain, that gun-powder may be fuppofid to ' be fo 
light: 
