280 Mr. Thompson’s Experiments 
It Is eafy to determine the velocity of the reccil in any given 
cafe, by fufpending the gun in an horizontal pofition by two 
pendulous rods, and meafuring the arc of its afcent, by means 
of a ribbon according to the method already defcribed, and this 
will give the momentum of the gun, its weight being known, 
and confequently the momentum of its charge. But in order 
to determine the velocity of the bullet from the recoil, it will 
be neceflary to find out how much the weight and velocity of 
the elaflic fluid contributes to it. 
That part of the recoil which arifes from the expanfion of 
this fluid is always very nearly the lame, whether the powder is 
fired alone, or whether the charge is made to impel one or more 
bullets, as I have found by a great variety of experiments. 
If therefore a gun, fu (pended according to the method pre- 
ferred, is fired with any given charge of powder, but without 
any bullet or wad, and the recoil is obferved, and if the fame 
piece is afterwards fired with the fame quantity of powder, and 
a bullet of a known weight, the excels of the velocity of the 
recoil in the latter cafe, over that in the former, will be pro- 
portional to the velocity of the bullet; for the difference of 
thefe velocities, multiplied into the weight of the gun, will be 
equal to the weight of the bullet multiplied into its velocity. 
Thus if W is put equal to the weight of the gun, 
U ~ the velocity of its recoil, when it is fired with 
any given charge of powder, without any bullet, 
V = the velocity of the recoil, when the fame 
charge is made to impel a bullet, 
B ~ the weight of the bullet, and 
v ~ its velocity,. 
It will be V = Hil!?, 
n 
1 
Let 
