Page:The Cornhill magazine (Volume 1).djvu/543

 3-pounder shot is 2·91 inches, or nearly three inches; and the surfaces they expose to the resistance of the air are 2·25, or 2-1/4 square inches, and 8·47 nearly, or nearly 8-1/2 square inches; that is, Mr. Whitworth's bullet, with the same weight to overcome it, meets with a resistance of a little more than a quarter that which the old bullet met with, and has the advantage of a sharp point to boot. Hence the enormous range attained,—9,688 yards.

The very same causes which make the fire of a rifle accurate, tend also to make it inaccurate, paradoxical as it may seem; but this inaccuracy being to a certain extent regular and known beforehand, is not of so much consequence, though it is a decided disadvantage. It may—not to be too mathematical—be explained thus:—The axis of rotation having, as we said, a tendency always to remain parallel to its original direction, when a rifle bullet or picket (the long projectile we have described) is fired at a high angle of elevation—that is, slanting upwards into the air, in order that before it fells it may reach a distant object,—it is evident from the diagram, that if the direction of the axis of rotation remains, as shown by the lines

No. 3. P   P    P    P    P    P    P gun

p p p, which represent the shot at different portions of the range parallel to the original direction in the gun, the bullet or picket will not always remain with its point only presented in the direction in which it is moving, but one side of the bullet will be partially opposed to the resistance of the air. The air on that side (in front) will be denser than behind, and the disturbing or deflecting influences before described will come into operation, the two opposite tendencies described in the text and the note to a certain extent counteracting one another. While at the same time the resistance of the air has a tendency to turn the bullet from the sideways position in which it is moving with respect to the line of flight (and the effect of this is the greater the less spin the bullet has to constrain it to keep its original direction), the result of which force, conspiring with the force described in the note, is to give it a slight angular rotation round another axis, and deflect the bullet by constantly changing its general direction (this second axis of rotation) to the side to which the rifling turns. This was exemplified in the late practice with Mr. Whitworth's gun. When firing at the very long range of 9,000 yards the 3-pounder threw constantly to the right from 32 to 89 yards.

The rotation of the earth about its axis tends to throw the projectile always to the right of the object aimed at. Space will not permit of