THE ROYAL ARTILLERY INSTITUTION. 
459 
resistance of the air. The centre of gravity should also be thrown far 
forward in order to give more stability, and less liability to upset (Eig. 12); 
long shot also are to be preferred as the curves which they describe are much 
more nearly parabolic than round shot. Eor short distances up to 100 yds. 
it was found by experiment with the old spherical musket ball, that a string 
three feet long might even be attached to it with effect, as greater stability 
was given to the axis, and the air acting on the string steadied the ball. 
In accordance with the heading of this paper, I have omitted all con¬ 
sideration of the unequal action of the resistance of the air due to the 
rotation of the projectile, as this more properly belongs to the subject of 
rifling. I do not of course mean to disparage its importance, as I consider 
it the chief cause of all deviations, when the qualities of the marksman and 
his weapon are not taken into account. What has been already treated of 
bears principally on mean radial deviations, for it is easy to conceive that 
the less the resistance, the lower will be the trajectory, and the more likely 
the projectile to hit the mark. 
Hygrometfic state of the Air . 
The hygrometric state of the air, and its density is the next subject to be 
considered under this head. This will naturally have the effect of increasing 
or diminishing the resistance, and the projectile should range the furthest 
with the lowest height of the barometer. The difference of range is eight 
yards in a thousand from this source, between the heights of barometer 
30 inches and 28 respectively. 
The effect of damp is however greatly to diminish the force of the 
explosion, and in consequence the range. Eobins writes, that he was not 
able to discover that the variation of density in the atmosphere affected in 
the slightest degree the initial velocity, but that the same quantity of 
powder, which in a dry day would communicate to a bullet a velocity of 
1700 ft. in 1", would not in damp weather communicate more than 1200 or 
1300 ft. in 1". 
There is one more subject of interest in this section, viz. the effect of the 
wind. I have never heard of any experiments on this subject, so I have 
been reduced entirely to theory, to furnish a notion of the disturbing force. 
I would premise however that I have taken no account of the increased 
amount of section of the side of the shot exposed to the action of the wind, 
due to the velocity w T ith which it moves through the air. True results 
however may be obtained by multiplying by some empirical coefficient of 
the form where V is the initial velocity, and p some function of the 
range. 
Tables III. and IY. give what I think will be the minimum deviations 
of certain projectiles under different circumstances. They are calculated 
from the important formula. 
Deviation = 
w 
where P is the pressure of the wind per square foot, C is a certain coefficient 
of effectiveness; A is the area of the side section; W the weight of the 
projectile. The coefficient should properly be determined by experiment. 
