THE EOYAL AETILLEEY INSTITUTION. 
49 
the expression denoting “worJc” namely PS* but is a necessary element in 
that which is a measure of momentum, namely Pgt .t 
Eor instance, suppose the elongated shot weighs 300 lbs. instead of 150 lbs. 
which is the weight of the spherical projectile. Then, as the average pressure 
on the two shot maybe considered the same, when equal charges are used; if 
M equal the momentum of the 150 lb. shot, the momentum of the elongated 
shot will be 1*4 M, and if t be the time of action of the powder on the 
gun in the former case, 1*4 1 will represent the time of action in the latter, 
namely, when the elongated shot is fired; therefore, in order to bring the 
strain and recoil within the assumed limits, the charge must not exceed 
25 lbs. of powder when a 3001b. shot is used, and, if the 3001b. shot be 
discharged with a greater charge than 25 lbs. of powder, the effects produced 
on the opposing shield by the two projectiles, namely, the 150 lb. and the 
3001b., will afford no criterion as to the relative merits of the two systems 
of ordnance in respect to penetration at moderate ranges. 
And if the charge be reduced so as to fulfil the two essential conditions 
as regards recoil and strain, the " stored-up work” (if the expression may be 
used) in the shot will be diminished in a corresponding degree, namely, by 
one-half. 
It is quite clear therefore that so far as "work done” on impact is 
concerned any increase in weight above the sphere must be positively 
disadvantageous within certain limits of range. J 
• P= average pressure acting upon the mass, S =distance through which this pressure acts, 
f P=average pressure acting upon the mass, g~ 32 or velocity generated by gravity in one 
second, £=time during which the average pressure acts. 
X In any experimental investigation of the subject, this principle must be duly recognized, or 
the most erroneous conclusions are likely to be drawn from the results of the trials. 
For instance, in the late trials at Shoeburyness against iron-plated targets it would be incorrect 
to measure the relative values of the two systems under consideration—namely, the light shot with 
the large charge, and the heavy shot with the small charge—by the effects produced on the targets; 
for the following Table will shew that the momentum of the shot, and therefore the strain on the 
guns and recoil were unequal 
Nature. 
Weight of 
projectile. 
Charge. 
Momentum, 
about 
Eemarks. 
lbs. 
lbs. 
68 -pr. iron gun. 
67-6 
16 
106,650 
110-pr. Armstrong gun. 
110-0 
14 
133,100 
»» » M . 
200 - 
10 
151,680 
120 -pr. shunt gun . 
140- 
20 
170,240 
However, the results obtained in these trials—although they cannot be taken to measure the 
relative values of the systems—practically demonstrated the great advantage in respect to pene¬ 
tration at moderate ranges, of the light shot and heavy charge over the heavy shot and light charge ; 
for, notwithstanding the comparatively small momentum of the 68-pr. shot, namely 106,000, it had 
nearly, if not quite as much effect on the target as the 1401b. shot with a momentum of 170,000; 
and although the 2001b. shot discharged from the 110-pr. with a charge of 10 lbs. of powder had a 
momentum of 161,000, it only indented the iron to a comparatively very small extent. 
[YOL. III.] 
7 
