102 PHILOSOPHICAL TRANSACTIONS. [ANNO 1781. 



when the powder was lighted at the vent 1.3, which was near the middle of the 

 charge, and rather greater when it was lighted at the top, or immediately behind 

 the bullet, than when it was lighted at the bottom. And by the recoil it would 

 seem, that the velocities of the bullets varied nearly in the same manner when 

 the charge consisted of 310 grains of powder. With 330 grains of powder, 

 both the velocity and the recoil were greater when the powder was lighted at the 

 middle of the charge, than when it was lighted at the bottom ; but they were 

 least of all when it was lighted near the top. And when an ounce of powder 

 was made use of for the charge, its force was greatest when it was lighted at the 

 bottom. But the difference in the force exerted by the powder which arose from 

 the particular position of the vent was in all cases so inconsiderable, being less 

 than what frequently occurred in repeating the same experiment, that no conclu- 

 sion can be drawn from the experiments, except only this, that any given charge 

 of powder exerts nearly the same force, whatever is the position of the vent. 



And hence the following practical inference naturally occurs, viz. that in the 

 formation of fire-arms, no regard need be had to any supposed advantages that 

 gun-smiths and others have hitherto imagined were to be derived from particular 

 situations for the vent, such as diminishing the recoil, increasing the force of 

 the charge, &c. ; but the vent may be indifferently in any part of the chamber 

 where it will best answer on other accounts : and there is little doubt but the 

 same thing will hold good in great guns, and all kinds of heavy artillery. The 

 form Mr. T. recommends for the bottom of the bore, is that of a hemisphere ; 

 and the vent to be brought out directly through the side of the barrel, in a line 

 perpendicular to its axis, and pointing to the centre of the hemispherical con- 

 cavity of the chamber. In this case the vent would be the shortest possible ; it 

 would be the least liable to be obstructed, and the piece would be more easily 

 cleaned, than if the bottom of the bore was of any other form. All these ad- 

 vantages, and several others not less important, would be gained by making the 

 bottom of the bore and vent of great guns in the same manner. 



A new* method of determining the velocities of bullets. — From the equality of 

 action and re-action it appears that the momentum of a gun must be precisely 

 equal to the momentum of its charge ; or that the weight of the gun, multiplied 

 into the velocity of its recoil, is just equal to the weight of the bullet and of the 

 powder (or the elastic fluid that is generated from it) multiplied into their res- 

 pective velocities : for every particle of matter, whether solid or fluid, that issues 

 out of the mouth of a piece, must be impelled by the action of some power, 

 which power must re-act with equal force against the bottom of the bore. Even 



* This method is not new ; as a specimen of it was given by Robins, in his New Principles of 

 Gunnery, prop. 1 1, p. 10*). Nor is the method generally true, as is proved in Dr. Hutton's Tracts, 

 p. 262. 



