270 
AUTOMATIC SIGHTING. 
Then A B F = Tangent angle of elevation. 
E B F = Quadrant angle of elevation. 
BCD — Angle of depression of object due to the 
height of the battery and the range, con¬ 
veniently called the range-finding angle. 
E B F = ABF - ABE. 
But ABE — BCD because E B was drawn parallel 
to DC. 
E B F — A B F — B C D. 
The angle B C D for ordinary heights can always be calculated 
from the formula. 
-p. • i • • i. Height in feet x 1146. 
Depression angle in minutes = ^ r -=- 
Range in yards. 
The condition to bo fulfilled then for automatic sighting, are that 
when the gun F B is elevated to any given angle to the horizon 
(quadrant angle), the tangent scale FA must at the same time be 
automatically raised to the height, representing the distance the shot 
will be thrown due to that quadrant angle, or vice versa if mechanism 
to fulfill the above condition is fitted to a gun, then whenever the eye 
looking over the sights sees the water line of the object, the gun will 
of necessity be at the right quadrant angle to hit that object. 
It may not be generally known that having a gun fitted with a 
quadrant elevation scale, a modified form of automatic firing may be 
carried out. Thus, suppose we wish to fire at a target at a distance 
of 2200 yards which is slowly coming in. We could place the gun at 
the quadrant elevation due to 2,100 yards, raise the tangent scale also 
to 2,100 yards, and fire the moment the sights are on the waterline of 
the target. It is evident that by so doing we have fulfilled the 
conditions given in Fig. 1, and that when the object is seen over the 
sights the target is at 2,100 yards. 
The condition of accuracy can be obtained from the equation. 
E B F = ABF — BCD , and are 
(a). That the range-finding angle BCD must be obtained with 
accuracy, in order to obtain the range for setting the 
tangent scale ABF. 
(bj . That any variation in the level of the platform will seriously 
affect the accuracy, in as much as it alters the quadrant 
angle E B F } and the angle of inclination of the sights. 
With regard to (a) it is clear that the greater the height the less 
any inaccuracy in obtaining the depression angle will affect the range, 
and a, short range will be far more accurately obtained than a long 
one. Take for example a height of 50 feet and 200 feet and ranges 
of 1,000 yards and 5,000 yards. 
