iSyg.] Measurement of Powder Pressures in Cannon, 365 
bore, with reference to the construction of guns, is evident 
from the fact that the strength of the gun must be adapted 
to the former and not to the latter. The inadequacy of the 
mode of determining, even relatively, the amount of pres- 
sures of very brief duration by the initial velocities of balls 
projected by them is shown by the effects of detonating- 
powders used in fire-arms: the barrel may be shattered 
while the ball is thrown with comparatively little force. 
The effect of increasing the charge of powder, compared 
with that of increasing the weight of the projectile, in 
augmenting the pressure was unexpected, and has to som: 
seemed almost incredible; although, as is not surprising in 
regard to a subject of such a nature, opposite views are held 
by men thoroughly conversant with artillery. 
Lbs. 
The mean of the pressures indicated at 1 inch from 
the bottom of the bore, with a charge of i£ lbs. 
of powder and a ball weighing, with its sabot, 
6*3 lbs. nearly, was 20,210 
With the same charge, at ins. from the bottom 18,150 
With i£ lbs. powder and a shot weighing 12*15 lbs., 
at i£ ins. from bottom 20,743 
With 2 lbs. powder and a ball of 6*36 lbs., at 1 in. 
from bottom 20,640 
With 3 lbs. powder and a ball of 6*43 lbs., at 1 in. 
from bottom 22,220 
The pressure in the cases in which shot of 12*15 lbs. 
weight were used, reduced to that which would be indicated 
at 1 inch from the bottom of the bore, on the supposition 
that the same difference would exist as with the smaller 
charges, would be 22,700 lbs., indicating that the effedt of 
doubling the weight of the ball (but with diminished windage) 
is not very different from doubling the weight of the powder 
— instead of increasing the pressure in a much greater ratio, 
as some have supposed. 
The results of the experiments with the musket barrel 
accord, so far as they admit of comparison, with those just 
stated. The manner in which an increased charge of powder 
may be supposed to affedt the pressure has already 
been referred to. The resistance of the forming gases 
in that part of the charge which is least confined, to the 
expansion of those in other parts of the charge, is perhaps 
most strikingly illustrated by the action of the fulminates, 
which, in quantities of a few grains, will, as is well known, 
VOL. ix. (n«s.) 2 b 
