COAST DEFENCE. 
189 
table of quadrant elevation for the high site and for the low site, read¬ 
ing to minutes and yards, and also make out a table of permissible 
errors in range for the high and low site, you will find that, although 
the actual permissible error in range from the high site is less than 
from the low, the permissible error in elevation, the cause over which 
we in the fort have control, is the same in both cases. That is to say, 
for a 9-inch gun firing at 1700 yards, the permissible error in elevation 
is eight minutes from either site, when firing at a target such as we 
have supposed; but the permissible error in range is, for the 250 feet 
site, 39 yards, and for the 29 feet site it is as much as 65 yards; or, in 
other words, you can make a mistake of eight minutes on the 250 feet 
site, and only get an error of 39 yards, whereas the same error on the 
29 feet site gives an error of 65 yards, getting on for double the former 
amount. This is where the fallacy has crept in—the effect has been 
considered without giving due consideration to the cause. 
The true comparison to make is, how far will the same error in 
elevation affect the same gun on a high and a low site? You will find 
practically no difference as regards the target without beam, but as 
the scale by which the elevation is given is more open, and therefore 
easier to read the higher you ascend, the chances are greater that the 
correct elevation is given to the gun on the high site. 
This will show you that the range tables issued for each gun only 
furnish (as far as six columns out of thirteen are concerned) the 
necessary data for you to reconstruct range tables suitable for the 
particular height at which your gun is mounted. Remember that 
the range tables are made out for target and gun on the same level, 
and that directly you fire at a target lower than your gun, then much 
of the data given in the tables requires modification. Take the 9-inch 
gun as an example. The range table tells you that on the flat 
five minutes’ elevation at 1700 yards makes a difference of 47 yards. 
Take the gun up only 100 feet, the difference is reduced to 34 yards, 
whilst at 250 feet the difference is 20 yards. Even 29 feet reduces 
the difference by 7 yards, 40 instead of 47. 
Again, on page 57 of your Drill Book, you must suppose the 
statement to refer to a very low site indeed (which, fortunately, is the 
exception rather than the rule). It states: “ If there is a difference 
of level in the racers of five minutes between trail extreme right and 
extreme left, this would mean, with a 9-inch or 10-inch gun, a difference 
of 50 yards at 1500 yards range.” At a height of 250 feet the error 
in range caused by five minutes’ irregularity of racer would be less 
than 16 yards in 1500. 
For this reason you can easily imagine that correction of fire is 
easier on the high site for gunnery reasons alone. Racer and tide 
corrections tend to disappear, and what is called, with great unfairness 
to the ammunition, “the powder correction,” becomes less, and 
proportionately the chance of error in giving it ought to be reduced. 
I understand that it has been necessary, when practising from some 
of the high-site batteries at Gibraltar, to increase the range beyond 
the usual limits, in order that the target may not be destroyed each 
