188 
COAST DEFENCE. 
in warfare. The best protection against the enemy’s fire is a well- 
directed fire from our own guns.” 1 
Let us now consider how height affects practice against a target such 
as we use, that has only length and freeboard, and is without the third 
dimension of beam. Lateral errors do not concern us in this investiga¬ 
tion, as height does not affect direction. 
Throughout your Drill Book you will find enumerated the various 
disturbing causes that affect the range. It does not particularly matter 
what the cause of error in range may be, but suppose our target is at 
A, we are firing from C, a low site, and for some reason the shot strikes 
at B, an error of AB. Now assuming the theory of rigid trajectory, 
which is practically true for small angles, let us suppose C on a height, 
and the round is repeated under exactly the same conditions; DA being 
now horizontal, the shot will strike at E, an error equal to AE, or less 
than that when firing from a low site. To take an actual example— 
8 oz. of powder added to the full charge of the 9-inch B.M.L. gun will 
increase its muzzle velocity about 8 feet per second (and I fear that 
variation from correct weight is not so uncommon as it should be). 
This increase of velocity on the flat means an increase of range of 30 
yards in 1700. At a height of 250 feet above the level of the sea this 
error is reduced to 20 yards—a very considerable reduction. For the 
sake of argument, let us suppose that we have perfect guns and ammu¬ 
nition, and accurate range-finding arrangements, and that the guns 
shoot exactly in accordance with the range table. Now, suppose one 
gun is in a fort 250 feet, and the other at a height of 29 feet above the 
mean level of the sea. These heights have been taken because they 
represent the heights of forts actually in existence, that need not be 
named. It is manifest, under the conditions, that when the gun is fired 
we hit or miss the target according to whether the gun is inclined at 
the correct angle or not to the horizon, the line being supposed to be 
correct. Further, there is a limiting angle of elevation between that 
necessary to strike the water-line and that to just graze the top of the 
target. Our targets are 12 feet high, so with the 9-inch guns this 
limit, which may be called the “permissible error in elevation,” is 
a very appreciable quantity. If you take the trouble to make out a 
Life of Farragut,” p. 218. 
