A'OL, LXVIII.3 



PHILOSOPHICAL TRANSACTIONS. 



295 



than the others, and the more so as it had a less length of the bore to move 

 through ; and if powder fire in time, which cannot be denied, though indeed that 

 time is manifestly very short, a greater quantity of it must remain unfired when 

 the ball with the greater velocity issues from the piece, than when that which has 

 the less velocity goes out, and still the more so as the bulk, of powder which was 

 at first to be inflamed in the one case so much exceeded that in the others. 

 The effect however will arise chiefly from the first and last of these 3 causes, as 

 that of the 2d will amount to very little; because the effect arising from the 

 greater velocity with which the fluid escapes at the vent and windage, is partly 

 balanced by the shorter time in which it acts. 



From the above reflections we may also perceive, how small the quantity of 

 powder is which is blown out unfired in any of these cases, and the amazing 

 quickness with which it fires in all cases : for though the time in which the ball 

 passed through the barrel, when impelled by the 8 oz. of powder, was not 

 greatly different from the half only of the time in which it was impelled by the 

 1 oz. it is evident that in half the time there was nearly 4 times the quantity of 

 powder fired. 



The 5th or last course was on the 21st of September, 1775 ; fine clear 

 weather, but a little windy. The machinery and the balls were of iron, but the 

 powder the same as in the last course, and the dimensions as follow : 



/) = 553 pounds, the weight of the pendulum. 



r= 101 inches, its length. 



gz=. TS\ inches, the distance of the centre of gravity. 



h = 84.775 inches = 7.065 feet, that of the centre of oscillation, the pen- 

 dulum making 68 vibrations in 100 seconds. 



