110 
CAPTAIN NOBLE AND ME. E. A. ABEL ON EIEED GUNPOWDER. 
both cases the projectile quitted the gun with the same velocity, and the mean pressure 
throughout the bore should of course have been the same. The chronoscopic records 
were, as they ought to be, nearly identical for the two rounds ; but the pressures indi- 
cated by the crusher-gauge were in the one round at the points A, B, C, 1, 4 (tig. 3, 
Plate 18), respectively 63*4, 41-6, 37*0, 41-9, and 25'8 tons on the square inch ; in the 
other, at the same points, respectively 28-0, 29*8, 3T0, 29-8, and 19-8 tons on the 
square inch. 
Where no wave-action exists, the chronoscopic pressures are generally somewhat 
higher than those of the crusher-gauge. The difference is not generally greater than 
about 5 to 7 per cent., although, in the case of some exceptionally heavy shot, this 
variation was considerably exceeded. Among the causes tending to produce this differ- 
ence may be cited : — 1. Friction in the parts of the crusher-gauge. 2. Slight diminu- 
tion of pressure due to windage *. 3. Vis viva of particles of the charge and products 
of combustion, a portion of which would be communicated to the shot, but would not 
take effect on the crusher-gauge. On the whole, however, the accordance of results 
derived from methods so essentially different was quite as close as could reasonably be 
expected, and entirely satisfactory. 
We now pass to the consideration of the tensions actually found to exist in the bores 
of guns. Two series of experiments were made by the Committee on Explosives with 
the 10-inch 18-ton gun. The one series was with charges of 70 lb. (31-75 kilos.) of 
pebble powder. The weights of the shot were made to vary, the first rounds being fired 
with projectiles of 300 lb. (136‘05 kilos.), and the weights being successively increased 
to 350 lb., 400 lb., 450 lb., 500 lb., 600 lb., 800 lb., 1000 lb., and concludingVith pro- 
jectiles of the weight of 1200 lb. (544-20 kilos.). 
In the other series charges of 60 lb. (27*21 kilos.) R. L. G. were used. The projectiles 
were of increasing weights as above; but the experiments were not carried so far, the 
heaviest projectile in this series being of 600 lb. (272 kilos.) weight. 
As we shall have occasion more than once to refer to these experiments, and as the 
powder used was carefully selected to represent as nearly as possible the normal service- 
powder of each description, it appears to us convenient, in order to illustrate the methods 
followed in determining the powder-pressures, to take an example from each series. 
This plan will further enable us to compare the difference of behaviour of pebble and 
R. L. G. powder in the bore of a gun. 
Commencing, then, with the charge of 70 lb. (31-75 kilos.) pebble powder and the 
projectile of 300 lb. (136-05 kilos.), the results given by the chronoscope, to which we 
shall turn our attention in the first instance, are given in Table IX. 
* In the experiments with, the 38-ton gun an opportunity occurred of determining the differences in pressure 
due to the escape of the gases by the windage, and it was found that a reduction of windage of -07 inch (1-75 
millim.), i. e. the difference between - 01 inch and -08 inch windage, reduced the maximum pressure indicated 
by the crusher-gauge by about 1 ton per square inch. Of course the mean pressure on the base of the projectile 
was not reduced in any thing like the same proportion. 
