55 
NOTE ON THE CORRECTION 
OF 
ARTILLERY EIRE. 
BY 
MAJOR P. A. MACMAHON, R.A. 
The question I propose to discuss here is as followsWhat is the best 
method of handling a single gun so that there may be the best possible 
chance of hitting an object (at first considered to be fixed) at a known 
or unknown range ? 
Artillerymen frequently have to fire at a fixed object, and it may, or 
may not, be convenient to obtain the range by a range-finder.\ In the 
former case, the range having been found, the gun may be laid for the 
range, and the projectile may, or may not, strike the object. If the 
object be sufficiently small the first shot will probably not be a hit. 
The reasons for this are clear; the range-finder may be at fault; the 
powder charge, or the projectile, or both, may be slightly abnormal ; 
the gun-layer may not be sufficiently well-trained; the gun or its 
mounting may be defective; the climatic conditions may be extraor¬ 
dinary ; and so on. 
Supposing lateral errors to be eliminated, if the gun were laid at the 
ranges indicated by the range-finder for a large number of shots, the 
points of impact would form a group of points, more or less scattered, 
along the line of fire ; the average range obtained would be a point 
called the centre of impact, and the density of the points of impact on 
the ground in the neighbourhood of the centre of impact would approx¬ 
imately obey the law known as the “ Law of Frequency.'” The nearer 
the points to the centre of impact the denser will they be. 
The centre of impact should coincide with the object if perfect shoot¬ 
ing is to be possible. The gun will be laid at the correct elevation if 
the result of a large number of shots is the production of a group of 
points of impact whose centre coincides with the object. The group 
will be more or less scattered according to the accuracy of the gun as 
measured by the true dimension of its 50 per cent, zone for the range. 
If the gun be perfectly laid, the percentage of hits depends entirely 
upon the size of the object, and an object could be so designed as to 
receive any desired percentage of hits. 
It is convenient to suppose that the object is a point on the range 
at a distance x yards from the gun. The artilleryman desires in the 
shortest space of time to arrive at the elevation he must give the gun 
2. VOL. XXI. 
