THE ROYAL ARTILLERY INSTITUTION. 
141 
pletion of the breach. (2) Breach on right face of bastion No. 11. Took 
18 hours, during which time 600 rounds were fired, being at the rate of 6 
to 7 rounds per foot run. 
General von Mertens, immediately after the capture of the town, reported 
the breach in No. 53 lunette as practicable after a little clearing. Breach in 
bastion 11 was reported quite practicable. 
It is proposed to give a translation of General von Decker's papers, so far 
as they relate, 1st, to the formation of a breach in lunette No. 53; 2nd, 
to the bombardment of the sluices. 
It may be first premised that the method of getting the range in each 
case was the same. The distance of the battery from the work being known 
from the map, and profiles of the fortress being at hand, the amount of charge, 
&c., due to the required “ angle of descent " necessary could be found from 
the range tables. The next thing to be done was to select some visible 
part of the work, and by firing a number of rounds, to find the “ point of 
mean impact" of the group. By consulting the plans of the fortress, data 
could be obtained by which the necessary amount of decrease of elevation of 
the gun and of deflection could be calculated, so as to hit the part where the 
breach was to be made. In this way the “ point of mean impact" of the first 
group of hits was transferred to a terminal point of the horizontal cut in the 
case of lunette No. 53, and to the face of the sluice in the other. Having 
thus commenced the starting point for the breaching at one end of the hori¬ 
zontal line, the “ point of mean impact" could subsequently be transferred 
to the other end, &c., &c. 
1. Breaching Face of Lunette No. 53. 
In the night of 11th—J 2th September, the third parallel, about 630 yds. 
in length, was thrown up in front of lunettes Nos. 52 and 53. It 
was decided to effect a breach in No. 53. With this view. No. 8 mortar 
battery was converted into a gun battery, and armed with four short 15 c.m. 
guns. The distance of the battery from the crest of glacis of the lunette 
was about 800 yds. 
The angle which the line of fire made with the face of the lunette was 55°. 
This was 5° less than the minimum angle at which a breach can be made 
satisfactorily, but it would have been difficult to get a better site, owing to 
the obstacles presented by the houses and gardens of Schiltigheim. The 
angle of descent of the projectile to hit the wall about 2 ft. above the water 
level, was found to be 7° 45'. The charge of powder, 1-7 lbs. 
At 7 a.m. on the morning of the 17th September, No. 8 battery opened 
fire. The distance was obtained with greater exactness by firing a few 
rounds with full charges at the parapet at the head of the work, and was 
found to be 910 yds. Practice was then made against the visible part of 
the parapet with charges of 1*7 lbs., and the “point of mean impact" after¬ 
wards transferred sidewards and downwards. The effect of the shells was 
watched by a range party placed in a trench between the second and 
third parallel, whence the glacis could be seen, but not the wall to be 
breached. 
The determination of the range took much time. As there was no tele¬ 
graphic communication between the range party and the battery, the “ cor- 
