306 
MINUTES OF PEOCEEDINGS OF 
If the projectile lias the same weight in both cases, the first result 
would be obtained by a short shell of large calibre, the second by a long 
shell of smaller calibre, the resistance of the air having a greater effect 
on the former than on the latter. The question is, which of the two 
systems would be preferable ? 
On the supposition that both shot graze the crest of the covering 
work and strike the scarp at the same spot, the mean velocities with 
which each passes over the distance between the counterguard and the 
scarp must be equal, as they have each dropped the same vertical 
distance, and therefore the times of flight over the space between the 
counterguard and scarp must have been equal. But the shell of large 
calibre is losing velocity faster than the shell of small calibre; therefore 
its velocity on passing over the crest of the counterguard must be 
greater, and its velocity on striking the scarp must be less, than that of 
the other shell. Therefore, the striking velocity of the shell of smaller 
calibre will be the greatest; but their weights are equal, therefore the 
energy of the smaller calibre will be the greatest. Moreover, the 
penetrating power of two projectiles are inversely as their diameters; 
the shell of smaller diameter will, therefore, have both the greatest 
energy and the greatest penetrating power. We should therefore 
choose for breaching with curved fire, a gun of small calibre throwing a 
long shell. The Prussians employ a short 15 c.m. gun, firing a long 
shell. The velocity required to be given being small, the short gun 
burns sufficient powder, and the long shell retains its velocity. There 
is, however, a limit to the reduction of calibre and lengthening of shell; 
for a very long shell “ wabbles 33 much if fired at a low velocity, and 
moreover is deficient in capacity for bursting charge. We may there¬ 
fore say that the gun and projectile chosen for breaching batteries 
should for a certain weight of projectile have the smallest calibre con¬ 
sistent with accuracy of flight of the projectile with the charge necessary 
to obtain the required angle of descent at the average range of breaching 
batteries, and consistent with a sufficient capacity for bursting charge. 
When the gun and projectile have been decided on, tables should be 
formed, by experiment and calculation, showing the angles of descent 
of the projectile at certain ranges, with different charges, and the 
angles of elevation to be given to the guns to obtain those ranges, with 
the different charges; and hence to deduce formulae by which to deter¬ 
mine the charge and elevation which must be used for the gun in any 
particular case, the range and angle of descent required being given. 
These problems have been worked out by the Russians and the 
Prussians, and it is most desirable that the same should be done for all 
the guns it is proposed we should use for siege purposes. 
Then, when a breach is required to be effected, the distance of the 
scarp from the battery having been ascertained by trial shots, and the 
height of the scarp and covering work, and the distance of the covering 
Work from the scarp being known, either from plans and sections of the 
Works or by reconnaissance, the charge and elevation to be given to 
the gun to strike the scarp wall at a given height can be calculated; and 
the guns are first laid so high that the shot strike a point that is visible, 
and then the point of mean impact of the shot is gradually lowered 
until the required part of the wall is struck, and the formation of the 
