VOL. LXXI.] PHILOSOPHICAL TRANSACTIONS. QJ 



Of the effect that the heat which pieces acquire in firing produces on the force 

 of powder. — It is very probable, that the excess of the velocity of the bullet in 

 the 2d experiment, over that of the first, was occasioned more by the heat the 

 barrel had acquired in the first experiment than by the position of the vent, or 

 any other circumstance; for Mr. T. found, on repeated trials, that the force of 

 any given charge of powder is considerably greater when it is fired in a piece that 

 has been previously heated by firing, or by any other means, than when the 

 piece has not been heated. Every body that is acquainted with artillery knows, 

 that the recoil of great guns is much more violent after the 2d or 3d discharge, 

 than it is at first; and on ship-board, where it is necessary to attend to the recoil 

 of the guns, in order to prevent dangerous accidents that might be occasioned 

 by it, the constant practice has been on board of ships, to lessen the quantity of 

 powder after the first 4 or 5 rounds. By the recoil it should seem that the 

 powder exerted a greater force also in the 4th experiment, being the 2d on the 

 Qd day, than it did on the 3d, or the 1st of that day; but the pendulum giving 

 way, it was not possible to compare the velocities of the bullets in the manner 

 we did in the 2 experiments above-mentioned. 



Concluding from the result of the experiments mentioned above, as well as 

 from other reasons, that the temperature of the piece has a considerable effect on 

 the force of the powder, Mr. T. afterwards took care to bring the barrel to a 

 proper degree of heat, by firing it once or oftener with powder each time he 

 recommenced the experiments after the piece had been left to cool. 



Of the manner in ivhich pieces acquire heat in firing. — Mr. T. was much sur- 

 prised, on taking hold of the barrel immediately after the experiment N° 17, 

 when it was fired with 330 gr. of powder without any bullet, to find it so very 

 hot that he could scarcely bear it in his hand, evidently much hotter than he had 

 ever observed it before, though the same charge of powder had been used in the 

 two preceding experiments, and in both these experiments the piece was loaded 

 with a bullet, which one would naturally imagine, by confining the flame, and 

 prolonging the time of its action, would heat the barrel much more than when 

 it was fired with powder alone. This, Mr. T. remarks, cannot happen from the 

 heat of the inflamed powder, but from the rapidity of its action on the piece, by 

 which the particles of the metal are put into a very quick vibratory motion, 

 which soon produces a great heat through its whole substance; like as when any 

 body is struck with a rapid blow by another hard body, even when cold ; and as 

 a bullet becomes hot when striking against any hard obstacle. This Mr. T. 

 illustrates in various instances, and then adds : 



Now the effort of any given charge of powder on the gun is very nearly the 

 same, whether it be fired with a bullet or without; but the velocity with which 

 the generated elastic fluid makes its escape, is much greater when the powder is 

 fired alone, than when it is made to impel one or more bullets; the heat ought 



vol. xv. O 



