88 I'HILOSOrHICAL TRANSACTIONS. [ANNO 1781. 



XV. New Experiments on Gunpowder, &c. By Benjamin Thompson,* Esq., 



F. R. S. p. 220. 



These experiments were undertaken principally with a view to determine the 

 most advantageous situation for the vent in fire-arms, and to measure the veloci- 

 ties of bullets, and the recoil under various circumstances. Mr. T. hoped also 

 to find out the velocity of the inflammation of gunpowder, and to measure its 

 force more accurately than had hitherto been done. 



These experiments, on the force of fired gunpowder, on the same principle of 

 those of Mr. Robins and Dr. Hutton, appear to have been made with great care 

 and accuracy, but on a small scale, being performed only with a musket barrel. 

 This and the other parts of the machinery were very nicely made, and contrived 

 to answer the several purposes ; which were, to determine the velocity of the 

 bullets, the recoil of the barrel, the effect of firing the charge in different parts 

 of it, the most advantageous situation for the vent, &c. Mr. T. had a contriv- 

 ance for shutting the vent as soon as the fire was communicated to the charge ; 

 and it is very certain, that no part of the elastic fluid made its escape by this 

 vent ; for, on firing the piece, there was only a simple flash from the explosion 

 of the priming, and no stream of fire was to be seen issuing from the vent, as 

 is always to be observed when a common vent is made use of, and in all other 

 cases where this fluid finds a passage. So that no part of the charge was lost by 

 the vent. The velocities of the bullets were determined by means of a pendulum, 

 into which they were discharged, according to the method invented by Mr. 

 Robins, and pursued by Dr. Hutton with cannon-balls, as described at p. 282, 

 &c. vol. 14. The chord of the arc, through which the pendulum ascended in 

 each experiment, was measured by a ribbon, according to the method invented 

 and described by Mr. Robins. 



The recoil was measured in the following manner. The barrel was suspended 

 in a horizontal position, and nearly in a line with the centre of the target, by 

 two small pendulous rods, 64 inches in length, and 25.6 inches asunder; which 

 being parallel to each other, and moving freely on polished pivots about the axes 

 of their suspension, and on two pair of trunnions that were fixed to the barrel, 

 formed, together with the barrel, a compound pendulum ; and from the lengths 

 of the vibrations of this pendulum, the velocity with which the barrel began to 

 recoil, or rather its greatest velocity, was determined. But in order that the 

 velocity of the recoil might not be too great, so as to endanger the apparatus 

 when large charges were made use of, it was found necessary to load the barrel 

 with an additional weight of more than 40 lbs. of iron. The chord of the arc 

 through which the barrel ascended in its recoil, was measured by a ribbon also; and 



Now Count ol' lUunf'ord. 



