THE ROYAL ARTILLERY INSTITUTION. 
143 
tell of! two or three guns of one of the batteries already existing for this 
special duty. The battery selected was No. 33, occupied by two companies 
of the Magdeburg regiment of garrison artillery (No. 4), which was armed 
with eight 15 centimetre steel guns. 
The first point was to determine the situation of the sluice in front of 
curtain 15-16, distant about 1950 yds. from No. 33 battery. Captain 
Kirchgessner first pointed out as a datum point a turret, supposed to be 
close by it, on the wall. A few rounds were fired, but the result showed that 
this could not be the turret in question, and the firing was resumed at 
another turret, which was hit after a few shots. This turned out to be the 
right one. A number of shots from each of the two guns was now fired 
at the exposed face of the turret, in order to determine as accurately as 
possible the “ point of mean impact v of the group for each gun. The 
projectiles used were the ordinary shells, the charge being 2J kilos. (5 lbs.) 
By applying the necessary corrections to the elevation and deflection, the 
“ point of mean impact ” was transferred to the middle of the face of the turret. 
The lines of fire on the turret being determined in this manner, calculations 
were made, based on the drawings of the fortress profiles and the local know¬ 
ledge of Captain Kirchgessner, for transferring, by corrections of the elevation 
and deflection, these lines of fire to a point on the sluice just above the water- 
level in the ditch. The middle of the face of the turret being a fixed point 
in the plans of the fortress, the distance of any part of the sluice also shown 
on the plans could be determined from it. Consequently a calculation could 
be made as to what amount of decrease of elevation and what amount of 
deflection would be necessary for the “ point of mean impact ” to be trans¬ 
ferred from the middle of the turret to the middle of the sluice. 
The guns being laid in this way, the bombardment commenced. 
Now came the question as to whether they hit the sluices or not. A 
reference to the practice tables showed that at this range about 8 or 10 per 
cent, of the projectiles might hit, if the guns were correctly laid on the 
sluice. With the naked eye it could be seen whether the shells hit the 
water, by the “sheaf ” of water which was thrown in the air; and by a 
comparison of the position and height of the “ sheaf” with the position of 
known objects in the fortress, inferences could be drawn as to where the 
shot struck. With a good glass it could be seen whether this sheaf of water 
was accompanied with a shower of wood or stone splinters. When this 
occurred it was concluded that the sluice was hit. 
The necessary corrections were finally applied, and the fire of the guns 
was directed so that the “ point of mean impact ” of each gun should strike 
the face of the sluice about 13 ins. apart, from which arrangement it was 
expected that the cones of destruction formed by the two shots would meet. 
When it was at all doubtful whether the projectiles were hitting the intended 
mark, shooting was resumed at the turret, being a visible object, as a check, 
in order to apply any correction which might be necessary on account of the 
weather, &c. 
The obtaining of the range of the sluice in front of lunette 63 was done 
in a very similar manner, but under less favourable circumstances. In this 
case the shooting was directed on the exterior slope of the left face of the 
lunette 63, and the exposed face being of less height than the turret, fewer 
hits could be obtained on it in proportion, and it was more difficult to 
