THE ROYAL ARTILLERY INSTITUTION. 
79 
zero-points of die index plates must either coincide with the directing 
line, or be at equal distances from it on one side or the other. An 
alteration in the direction is effected by moving the rear zero-point to 
right or left—of course with due regard to the position of the front one 
at the time. 
As regards the amount of the correction to be made, the following is 
the rule to be observed :—If both the zero-points of the index plates 
are on the same side of the directing line, the difference of the dis¬ 
tances must be equal to the amount of the necessary correction. If, 
however, one zero-point is to the right and the other to the left of this 
line, the sum of the distances gives the correction. If it is wished, for 
instance, to increase (or diminish) the deflection by 1, 2, 3,. mm, 
the relative difference of the distances must be larger (or smaller) by 
1, 2, 3,. mm. In using this aligning apparatus the distances of 
the zero-points from the directing line, to the right or left—in other 
words the resulting sums or differences—are to be noted at every 
round, so that it is always known what amount of alteration it is neces¬ 
sary to make. 
By making use of this aligning apparatus all lateral errors in laying 
are reduced to a minimum, and the laying becomes independent of the 
amount of light, and can be performed with certainty, even at night. 
When enfilading at long ranges, or when bombarding the interior of 
a work, if the object to be struck can be seen from the gun, the laying- 
can be carried on just as in the case of direct fire. If this is mot the 
case we have to lay on a point (to be determined-upon by help of a 
plan) of the cover nearest the object, which will give such a line of fire 
that the terreplein shall be taken as nearly as possible in the direction 
of its greatest length. In this case we should only make use of the 
point of aim in the cover for the purpose of giving the necessary 
direction to the axis of the piece by means of the deflection scale. The 
elevation will have to be given by the quadrant. 
As, however, the selected auxiliary point of aim is liable to be 
knocked away, it is only used as a guide for the first shot. When 
the gun has been laid the directing plates are fixed to the platform in 
such a manner that their corresponding longitudinal edges coincide 
with the zero-points of the index plates when let down. Any subse¬ 
quent alterations in direction that may be required are effected by 
means of the aligning apparatus. 
In enfilading single faces at the shorter ranges (with ricochet fire), 
the elevation is also given by means of the quadrant. To get the gun 
so placed that its plane of symmetry shall coincide with the plane of 
alignment ( Richhtngs-JEbenc ) the plumb-line and pickets are made use. of. 
The latter must be set up separately for each gun, and with their 
direction either parallel to the crest of the work to be enfiladed, or 
making a small angle with it. The direction and its correction are 
given by means of the aligning apparatus. 
As the prolongation of the interior crest can only be found with 
great difficulty, it is better to get the prolongation of the exterior crest 
instead. 
The lines of direction (Directions Linien ) of the individual guns are 
11 
