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 of the air we have mentioned can come into operation, as the resistance is equal on all sides; and not only that, but if there are any irregularities on the surface of the ball, as they are brought rapidly first on one side and then on the other of the point or pole of rotation, they can have no effect in deflecting it to one side more than to the other. Hence the accuracy, or straight shooting, of our modern gun, the rifle.

We have before mentioned that Robins pointed out the enormous effect of the resistance of the atmosphere to the passage of a shot; and "because," as he says, "I am fully satisfied that the resistance of the air is almost the only source of the numerous difficulties which have hitherto embarrassed that science," viz. gunnery, he considered it above all things necessary to determine its amount; for which purpose he invented the Ballistic Pendulum and Whirling Machine. His experiments were made principally with small bullets; but a more extended series of experiments was made by Dr. Hutton with the same machines, and on the Continent and in America by Major Mordecai, with a ballistic pendulum of improved construction. It appears from these that when a ball of two inches diameter is moving with a great velocity, it meets with a resistance of which the following examples will give an idea: at a velocity of 1,800 feet per second the resistance is 85-1/2 lbs., and at a velocity of 2,000 feet, 102 lbs. If we wish to increase the range, then, we must overcome this resistance in some way. As the resistance is nearly proportionate to the surface, that is, twice as great on a surface of two square inches as on a surface of one square inch, we must do so by increasing the weight of the shot. For it is evident that if two shot of different weights start with the same velocity, and meet with the same resistance, the heavier one, having the greater momentum, will maintain its velocity the longest. Throw a cork and a stone of the same size with the same force—the cork will only go a few yards, while the stone will go perhaps ten times as far. In the smooth-bored cannon this could only be effected partially by increasing the size of the shot, when the surface exposed to the resistance of the air increased only as the square of the diameter, while the weight increased in a greater ratio, as the cube of the diameter. Hence the longer range and greater penetration of heavy guns. As, however, with a rotating body the tendency is always for the axis of rotation to remain parallel to its original direction—thus a top while spinning may move about the floor, but remains upright on its point, and does not fall till the spin is exhausted—we have with rifles a means by which we can keep a bullet always in the same direction. In order to comply with the condition, then, of exposing a small surface to the resistance of the air while the bullet's weight is increased, we reject the spherical form, and make it a long cylinder; and to make it the more easily cut through the air, we terminate it with a conical point.

Thus compare Mr. Whitworth's 3-pounder with the ordinary or old 3-pounder; the shot weigh the same, but the diameter of Mr. Whitworth's 3-pounder shot is 1·5 or 1-1/2 inches, while the diameter of the old