120 
CAPTAIN NOBLE AND MR. F. A. ABEL ON FIRED GUNPOWDER. 
The results of Table XIV., in comparison with those of the other mode of calcula- 
tion (Table XIII.), are graphically compared in Plate 21. It will be observed that, as 
in the case of pebble powder, the two methods give values closely accordant ; and if 
Plate 21 be compared with Plate 20, the differences in velocity and pressure at the 
commencement of motion between the two natures of powder are very strikingly shown. 
Thus it will be observed that with pebble powder the maximum pressure, 2745 atmo- 
spheres, is reached when the projectile has moved ’5 foot (T52 metre), and at about 
•00437 second after the commencement of motion. With R. L. G. powder the 
maximum pressure, 3365 atmospheres, is reached when the projectile has moved only 
•05 foot (*015 metre), and at about -00070 second from the commencement of motion. 
The first foot of motion is, with the one powder, traversed in about '0025 second, with 
the other in about '0051 second. 
The pressure given by the crusher-gauges in the experiments with It. L. G. under 
discussion (and these pressures should be compared both with those given in Table XIII. 
and with the crusher-gauge pressures furnished at the same points by pebble powder) 
were, at A, B, C, 1, and 4 respectively, 44-2, 30-3, 22-5, 13-5, 12 tons per square inch, 
or, in atmospheres, 6731, 4614, 3426, 2056, and 1827. 
In deducing the pressure from the velocity, we of course assumed that the gaseous 
products of combustion acted on the projectile in the manner in which gases are 
generally assumed to act. 
With the slower-burning powders this hypothesis appears to be not far from the 
truth ; but with the more explosive powders the crusher-gauges show that the powder 
acts on the shot, as we have already observed, by a succession of impulses ; and in this 
case the curve of pressures derived from the chronoscopic observations must be taken to 
represent the mean pressures acting on the projectile throughout the bore. 
With the various powders experimented on by the Committee on Explosives, there 
have of course been very great variations in the pressures indicated. 
The highest mean pressure indicated by the chronoscope was 3(16 tons, 4660 atmo- 
spheres ; and this pressure was attained with a charge of 60 lb. II. L. G., and a projectile 
weighing 400 lb. In the same series, the highest local or wave-pressure exhibited by 
the crusher-gauges was 57*8 tons, 8802 atmospheres ; but this excessive pressure was 
exhibited only in the crusher marked A in Plate 18. fig. 3, and was probably confined 
to that particular point. The pressures exhibited by the same powder in the same 
round, at the points B and C in the powder-chamber, were respectively 37 tons, 5634 
atmospheres, and 29-6 tons, 4507 atmospheres. 
But although, in the various guns and with the various charges and special powders 
experimented with, the pressures at different points of the bore exhibit, as might be 
expected, marked differences, these differences almost altogether disappeared when 
powders of normal types and uniform make were experimented with, and when the 
pressure was referred, not to fixed positions in the bore of the gun, but to the density 
of the products of combustion. 
