348 
MINUTES OF PROCEEDINGS OF 
We have now to consider the effect of the force of the wind on the 
line of flight, and to calculate the deviation from this cause. 
Let p — pressure of wind in pounds per square foot, 
A = area of longitudinal section of shot in square feet; 
then pA will represent the pressure of wind on side of shot tending to 
turn it out of the original line of flight. 
If the shot were perfectly smooth, the effect of the wind on its side 
would be \pA; but since the surface of the projectile is rough, both at 
the sides and at the base, and as it is, moreover, furnished with 
numerous studs, I have estimated that the pressure will be fairly repre¬ 
sented by pA; and from the calculation of many practice tables I 
believe this to be practically accurate. 
Sir Henry James, K.E., gives the following ratio of pressure to 
velocity of wind :— 
p = *005 V 3 in miles per hour; 
or^ = '00232438 F 3 in f.s. 
Now, if we regard the wind as a constant force blowing across the 
range, and acting uniformly on the projectile, we shall have a curve 
resembling a parabola as the path of the latter; and for heavy shot and 
short ranges* or light winds, this method would give tolerably accurate 
results, and would only require the simple formula 
S = t 2 p sin D ~ 
1 2 w 
— deviation in ft. 
This equation is not accurate enough for light shot and high winds, 
since the wind communicates a certain amount of sideways or crab-like 
velocity to the projectile, and would ultimately cause it to travel as fast 
across the range as the wind itself is travelling. 
It is clear, then, that the pressure of the wind on the side of the 
shot is that due to the difference between the sideways velocity of the 
latter, and the velocity across the range of the former. 
Putting v as the sideways velocity of the projectile, communicated to 
it by the wind, we have 
W sin D — v 
as the difference between velocities of wind and shot across the range; 
and thus, to find the pressure, we have 
p = *00282438 {W sin D - vf. 
Putting/ 1 as the force of the wind acting on the side of the projectile, 
we have 
f: g :: pA j w; 
pAg_ 
w 
= •0023 2438^ ysinj) _ 2 
w 
— a {W sin D ~ v) 2 ; 
where a is a constant for each nature of projectile. 
