CAPTAIN NOBLE AND MR. E. A. ABEL ON EIRED GUNPOWDER. 
121 
We have already referred to the experiments made with cylinders gradually in- 
creasing in weight in the 10-inch gun. A similar series was made in the 11-inch gun 
with charges of powder of 85 lb. (38*56 kilos.); and as the series in both guns were 
made with great care and under as nearly as possible the same conditions, we selected, 
in the first instance, the experiments with pebble powder, in these guns to test the 
accordance or otherwise of the tensions, under the varied conditions of experiment, when 
taken simply as functions of the density. 
The results of these calculations are graphically represented in curves 1 and 2, 
Plate 22 ; and it will be observed that with these different calibres and charges the 
tensions developed are as nearly as possible identical. 
Curves 3 and 4 on the same Plate exhibit the results of similar calculations for 60 lb. 
R. L. G. fired in the 10-inch gun, and 30 lb. R. L. G. fired in the 8-inch gun. In this 
case also, although there are differences between the curves representing the pebble and 
R. L. G. powders, to which we shall allude further on, the accordance between the same 
description of powder fired from the different guns is almost perfect. 
S. EEFECT OE INCREMENTS IN THE WEIGHT OE THE SHOT ON THE COMBUSTION AND 
TENSION OE POWDER IN THE BORE OF A GUN. 
In our preliminary sketch of the labours of previous investigators, we alluded to the 
views held by Robins and Rumford upon the rapidity of combustion within the bore. 
The latter, relying chiefly upon the fact that powder, especially when in very large 
grains, was frequently blown unburned from the muzzle, concluded that the combustion 
was very slow. Robins, on the other hand, considered that, with the powder he employed, 
combus’tion was practically completed before the shot was materially displaced ; and 
it is not easy to see why the unanswerable (if correct) and easily verified fact of which 
he makes use has received so little attention from artillerists. 
Robins, it will be remembered, argues that if, as some assert, a considerable time is 
consumed in the combustion of the charge, a much greater effect would be realized from 
the powder where heavier projectiles were used, but that such is not the case. 
The Committee on Explosives have completely verified the correctness of Robins’s 
views. 
In the 10-inch gun, with a charge of 60 lb. (27*2 kilos.) R. L. G. powder, the work 
realized from the powder is only increased by about 5 per cent, when the weight of 
shot is doubled. 
In the slower-burning pebble powder, with a charge of 70 lb. (31*75 kilos.), with a 
similar increase in the shot, the greater effect realized was about 8^ per cent. ; but 
when the weight was again doubled (that is, increased to four times the original weight), 
the additional effect was barely 1 per cent. 
Piobert’s views, moreover, that the pressure exercises but a trifling influence upon 
the rate of combustion, appears to us entirely untenable. With a particular sample of 
service pebble powder, we found the time required for burning a single pebble in the 
MDCCCLXXV. R 
