460 
ADJUNCTS OP DEFENCE. 
employment of either adjunct, and, in the interests of efficiency and 
economy, it must apparently be worth while to seek to arrive at these 
limitations. 
The Position-Findee. 
Accurate tire from permanently mounted guns at a stationary target 
depends on the exactitude and accuracy with which at least four 
separate conditions, independent of the gun itself, are, viz.:— 
{a.) A line observed by eye. 
( b .) An ascertained range. 
(<?.) Correction for drift. 
(d,) Correction for wind. 
(To the above may have to be added in some cases a correction for 
variability in powder). 
Of these conditions, the first (a) can be met by (1) sighting pure 
and simple ; (2) sighting for direction only ; (3) a telescope with cross¬ 
hairs attached to the gun; (4) a telescope separate and at a distance 
from the gun. The second (b) can be fulfilled by suitable instruments, 
or (with loss of time and ammunition) by trial shots alone. The third 
(c) is a mere clerical matter; the fourth (d) is largely a question of 
unaided judgment, i.e. } of practical experience. 
The relative importance of the fulfilment of these conditions in 
regard to accuracy of fire varies somewhat according to circumstances. 
Thus, in firing at a square target of small dimensions, the non-fulfil¬ 
ment of any single condition will ensure failure ; (a), (b), and (c) may 
be exact, but a wrong estimate of wind correction will cause the shot 
to be thrown away. In this case, therefore, assuming equal care to be 
taken in performing each operation, the relative importance will depend 
upon the probability of the limit of permissible error being exceeded. 
In eacli operation, error up to a certain point will not vitiate the result. 
In which, operation is that limit of error most likely to be exceeded— 
in the purely visual operation (a); in the determination of range (b) ; 
in the wind correction (< d ). 
Assume that the length of target is great in proportion to its 
height, as in the case of a ship 5 s broadside, then errors in direction 
become of less importance than those in elevation. In other words 
(tf), 1 (c), and (d) become of relatively less account, and success turns 
merely on the fulfilment of (b ). 
If the target is moving, the question becomes complicated by the 
need for a further correction which affects ranges if the motion takes 
place along a line passing through the gun, and range and direction in 
varying degrees according to the obliquity of the path. Thus this 
correction usually involves two variables, and is practically a prediction 
of the position of the target at the moment when the projectile will 
reach it, such prediction being based on observations previously made. 
What now are the special functions of the position-finding system, 
and how far does it tend to reduce the elements of error above pointed 
i Except possibly when ordinary sights are used, and yisual errors in eleyation therefore 
become possible. 
