69 
THE ROYAL ARTILLERY INSTITUTION. 
The first angle is too large, and the second too small; therefore,, 
taking* a mean charge of 0*75 k.g., we shall have 
7l =16° 81V. 
This charge may be looked upon as the right one. 
We now interpolate for the angle of elevation corresponding bo a 
charge of 0*75 k.g. and a range of 1278 metres, and obtain 
(j) 1 = 15° 59V- 
As this angle is taken with reference to a line inclined at an angle 
of 23V; the angle of elevation, as taken with reference to the hori¬ 
zontal, must be increased by 23V; and we shall have 
0 O = 16° 23'. 
8. Method of Proceeding when a Breach has to be Effected by 
means of Cannelures cut out by Curved Fire. 
Owing to the natural dispersion of the projectiles it will very seldom 
be possible, when breaching by means of curved fire, to cut out the 
horizontal cannelure with the same accuracy as in the case of direct 
breaching at short ranges, where we commence at one end and shift 
each individual shot laterally. We have to content ourselves with 
grouping the hits round certain fixed points by firing 3 to 5 shots at 
a time with the same laying. According to the observed effects the 
groups of hits are shifted laterally to a given amount by altering the 
laying, and in this way a horizontal cut is gradually formed. By a 
continual repetition of this process the cut becomes deeper and deeper 
until the scarp is completely penetrated. 
In order to carry out this process with uniformity, and to be able to 
tell at any instant how many times the cut has been fired at from one 
end to the other, a table is set up in each breaching battery, in which 
is registered the line of direction of every group of shots delivered. 
It is not advisable to cut right through the scarp in one place, and 
then enlarge the breach till it becomes a horizontal cut. In the case of 
thick scarps a deep funnel is formed, from the sides of which the pro¬ 
jectiles rebound and explode prematurely. Moreover, the funnel 
becomes filled with the iron splinters, and the penetration of the shells 
is thereby rendered difficult. 
Should the scarp be a very strong one, or should there be reason to 
apprehend that, owing to the line of fire being oblique, the shells will 
glance off, we should fire a larger number of them with the same 
laying and at one particular spot. If plenty of guns are available, or 
if the scarp is not very strong, we can commence with half the number 
at one end, and with the remainder at the centre of the space to be 
breached. Lastly, if we are prevented, either by traverses or by the 
narrowness of the ditch which has been selected to fire down, from 
making a breach of sufficient extent, we must cause the guns to cross 
