378 
MINUTES OF PllOCEEDINGS OF 
From the varying quality of the powder, from the varying resistance of the air 
on different days, from the inevitable inequalities in the weight and in the position 
of the centre of gravity of the projectiles, there result certain irregularities in the 
trajectories, even with rifled guns, which it is impossible to avoid. 
(2) The guns as manufactured are not perfectly identical; hence too arise 
certain differences in the trajectories. Experience has shown that out of a batch 
of perfectly new guns, firing equal charges, with the same elevation and atmospheric 
circumstances, some shoot further and others shorter than they should under the 
given conditions. The peculiarities of each gun, then, should be ascertained, so as 
to discover how far the elevation and allowance for drift for each range as ascer¬ 
tained by calculation agree. This peculiarity again is to a certain extent prejudicial 
to the probability of a hit. 
(3) Bronze rifled guns wear from the friction between the driven surfaces of 
the projectile and the driving surfaces of the piece; the wear increases by long 
service and gradually diminishes the probability of a hit. Although the endurance 
of bronze guns may be said to be perfectly satisfactory, still the above circum¬ 
stance must be borne in mind in questions of probability. 
(4) The gun is not always laid with the same accuracy and uniformity at 
practice, still less so before an enemy; this, once more, introduces variation in the 
trajectories and therefore is prejudicial to the probability of a hit. 
(5) The estimation of the distance of the object to be fired at is difficult at 
short and much more so at long distances; usually the estimate is more or less 
erroneous; the error thus introduced extends to the elevation of the gun and the 
allowance for drift, and finally, to the trajectory; thus the probability of a hit is 
diminished. 
(6) A wind blowing in a direction non-coincident with the line of fire exerts a 
more prejudicial influence on the elongated projectiles from rifled guns than on the 
round shot of smooth-bores, inasmuch as the former projectile opposes a larger 
side surface to the wind, and consequently deviates more from the intended 
direction. 
(7) With shrapnel shells the probability of a hit of the splinters of cast-iron 
and bullets depends chiefly on the regularity of the burning of the fuze; the rings 
of composition of the latter vary in time of burning; this is partly due to the 
varying condition and density of the composition, and partly to the temperature 
and hygrometricity of the atmosphere: these variations are more particularly 
observable at long ranges. 
(8) The more extended range of rifled guns lessens the probability of a hit so 
far, that the various influences which cause divergence of the projectile have a 
longer time to act upon it, and consequently cause greater irregularity. 
After having thus detailed the various elements affecting the probability 
of a hit, we have now to show the actual probability of the mountain gun. 
The probability of a hit may be estimated, either by the ratio of the 
number of hits in a given object at a certain distance to the number of 
rounds fired ; or by the dispersion of the first grazes, both as to length of 
range and width of side deviation. 
The following tables, the results of experimental practice, give the 
necessary information as to the probability of a hit of the various projectiles 
fired from the 3-pr. mountain gun. 
