V
Now, however good the ball might be, the chances would be against a perfect stillness upon any axis during flight; that is, of course, when no initial spin was imparted to it by the way in which the stroke was played. It would very likely turn just a little upon an axis, and that little would unsteady and injure its flight, inasmuch as the wobble would be from side to side alternately. This difficulty can be got over by imparting an initial spin to the ball which will always be the same all through its flight, and which will thus stop the wobbling. In a word, rotation will steady the flight. This idea was originally at the bottom of the rifling of the barrel through which a bullet is projected; certainly it was the fundamental principle of the rifling of the old 32-pounders. Better to make the ball rotate on an axis that you know about than that it should wobble on one you do not know about, they said; and so the tubes were rifled inside, the balls were made to rotate, and their flight was made steadier and therefore longer.
In the very earliest days of his investigations upon the flight of the golf ball, Professor Tait thought of the application of this idea to the game. A rotation should be given to the ball to steady its flight and make it longer. A moment’s thought on the part of those whose rudimentary scientific knowledge is a little rusty, will indicate that there are three definite and clearly distinguished axes of rotation. One is a vertical one, and it is chiefly upon that axis that the golf ball rotates when it is pulled or sliced, or upon an axis that has something of the vertical element in it. Then there is the horizontal axis, which is at right angles to the line of flight; and this is the axis upon which it rotates when either under-spin or top has been applied to it. And, thirdly, there is the horizontal axis, which is parallel with the line of flight. This is the axis upon which the rifle bullet spins. At first Professor Tait was inclined to the idea that the last-named would be the ideal axis for the rotation of the golf ball, but it happens to be the one upon which it is impossible to make it rotate when struck by a golf club. However, in this detail of his preliminary theorising he was wrong, due entirely to his not having then investigated the virtues of under-spin as always given to a ball when well driven, and not having come by the great discovery that this under-spin helped the ball to resist gravity and prolong its flight as nothing else could. How exactly under-spin does this, we have just seen, and readers will now have a very definite perception of the qualities of a ball and the importance of rotation, and though the chief advantage of rotation is in resisting gravity, it is an incidental advantage of it, as will now be understood, that the flight of the ball is thereby steadied, and a very slight inaccuracy in centering made of less consequence than it would otherwise be. But remember that a considerable inaccuracy in centering will interfere with the rotation, and therefore the bad flying ball can still be distinguished, because it will fly badly.