Page:The Cornhill magazine (Volume 1).djvu/541

 shot, for it was not only that the bullet did not go in the direction in which it was aimed, but it did not even follow the direction in which it started. This was well shown by Mr. Robins in the experiment we commenced with. He bent the end of a gun barrel to the left, and aimed by the straight part. As would be naturally expected, the shot passed through the first tissue-paper screen 1-1/2;**P2 unclear] inches to the left of the track of a bullet, which had been previously fired from a straight barrel in the same line with which the crooked barrel had been aimed, and 3 inches to the left on the second screen; but as he had predicted, and as the company could hardly have expected, on the wall which was behind, the bullet struck 14 inches to the right of the track, showing that though it had gone at first as directed by the bent portion of the barrel, yet as the bullet in being turned had rolled against the right-hand side of this portion of the barrel, it had a rotatory motion impressed upon it, by which the anterior portion moved from left to right, and the bullet, after moving away from, turned back and crossed the track of the other bullet again, or was incurvated to the right.

We now see why spherical bullets from a smooth bore, though they may fly almost perfectly accurately a short distance, cannot be depended on in the least for a long distance, as the bullet which might strike within 1 inch at 100 yards would not strike within 2 inches at 200 yards, and still less within 3 inches at 300 yards of the mark at which it was fired.

The cause of these deflections we have seen is almost wholly rotation or spin. The object of the rifle is to place this rotation under our control, and if the bullet must spin, to make it spin always in the same direction, and in the way which will suit our purpose best. With this object the interior of the cylindrical bore which we have been considering as smooth, is scored or indented with spiral grooves or furrows. As we are merely concerned with the principles, and not with the constructive details, we need only mention that the number of these grooves varies in different rifles from two to forty; that their shape and size, though dependent on certain conditions, is, we might almost say, a matter of fashion; and that Mr. Whitworth, in his almost perfect rifle, uses a hexagonal bore, and Mr. Lancaster makes a smooth oval-bored rifle; but that in all, the deviations from the circle of the interior cylinder do not pass straight from end to end of the barrel, but spirally, and constitute, in fact, a female screw. The bullet, fitting tight and entering the grooves, is constrained to rotate while being forced out of the barrel by the gunpowder, in the same manner that a screw is necessarily twisted while being drawn out of a hole or nut; and this rotation or spin being impressed upon it by the same force which projects it from the barrel, continues during the flight. This spin is different in direction from those we have been considering previously; it is like the spin of a top thrown point foremost, the axis of rotation coincident with the line of flight. While it remains in this position (coinciding with the line of flight) none of the deflecting effects