Therefore, when a ball is sliced, it is made to spin round so that its front side moves round constantly to the right, and, in accordance with the law just mentioned, there is a greater atmospheric pressure on the left side than on the right, and, consequently, the ball is pushed away to the right--as we see it. When it is pulled, the spin is in the opposite direction, and the extra pressure is from the right, and so it is sent away to the left. When the ball is topped the spin on the front side is downwards, and the ball ducks--the extra pressure this time being in the same direction as gravity; and when under-cut is applied, and under-spin follows, the front side of the ball is spinning upwards, and the extra pressure is from below and against gravity. When this conclusion was first briefly stated, golfers resisted the suggestion that when driving they imparted any under-spin to the ball; but the Professor stuck to his point, and proved it beyond doubt, and it is in this way that the ball takes six and a half seconds over its flight instead of the three and a half that it would otherwise do; and he proved, moreover, that if there was no under-spin imparted to it when driving it would only travel about half the distance that it usually does. The greater the under-spin the greater the upward pressure, and this conclusion leads to others very interesting. IV Golfers are in the way of saying that this ball “flies well” or that the other ball “does not fly well.” Sometimes it is imagination born of lack of form; but when great players concur it is not imagination. Some balls are obviously better than others--made of better material, better elastic thread, and more carefully constructed. There is an evident reason why such balls should fly better than others; that is to say, why they should go off the club more quickly, keep their place in the air longer, and travel farther. But then there are many balls of absolutely first-rate quality--and maximum price--that vary considerably in their flying properties, and it very commonly happens that even balls out of the same box, made at the same time and in the same way and of the same stuff, vary also. One frequently finds one or two “bad” balls in a box, and one or two very good ones. The excellent player very soon knows when he has come by the good ones and the bad ones. Now why, under such circumstances, should these balls vary so? What is it that makes them vary? Golfers in general do not know. Often enough they put it down to “pure cussedness”; others, to an idea that it is due to some accidental flaw in the manufacture. It is neither the one nor the other.