238 Count Rumford’s Experiments to determine 
repeated firing. With the same charge, the recoil of a gun, 
(and consequently the velocity of its bullet), is greater after 
the gun has been heated by repeated firing than when it is cold. 
The velocity of the bullet is considerably greater when the can- 
non is fired off with a vent tube, or by firing a pistol charged 
with powder into the open vent, than when the vent is filled 
with loose powder. The velocity of two, three, or more fit 
bullets discharged at once from a piece of ordnance, compared 
to the velocity of one single bullet discharged by the same 
quantity of powder, from the same cannon, is greater than it 
ought to be according to the theory. Considerable quantities 
of powder are frequently driven out of cannon and other fire- 
arms unconsumed. The manner in which the smoke of gun- 
powder rises in the air, and is gradually dissolved and rendered 
invisible, shews it to partake of the nature of steam. But not 
to take up too much time with these general observations, I 
shall proceed to give an account of experiments the results of 
which will be considered as more conclusive. 
Having found it impossible to measure the elastic force of 
fired gunpowder with any degree of precision by any of the 
methods before mentioned, I totally changed my plan of ope- 
rations, and instead of endeavouring to determine its force by 
causing the generated elastic fluid to act upon a moveable body 
through a determined space, I set about contriving an appara- 
tus in which this fluid should be made to act, by a determined 
surface, against a weight, which by being increased at pleasure 
should at last be such as would just be able to confine it, and 
which in that case would just counterbalance and consequently 
measure its elastic force. 
The idea of this method of determining the force of fired 
