Another point is extremely interesting. Some golfers no doubt think that in driving they have to cock their balls up in the air, so to speak; that is to say, that they have to aim at an upward trajectory from the beginning. As a matter of fact they have to do nothing of the kind, and as a matter of common knowledge the best balls, as driven by a Vardon or a Braid or any other first-class player, always “start low” and keep a path quite close to the ground for some distance, after which they begin to rise. If there were no under-spin the ball could not keep this horizontal path for the time that it does; still less could it begin to rise afterwards. It is the under-spin that does it, and the theoretically perfect drive is the one that is hit straight forward with practically no initial elevation or incline. The character of the stroke gives to the ball the necessary under-spin and power to rise, and the way in which the club comes on to the ball in a stroke so perfectly executed makes any considerable initial elevation impossible, just as it is not wanted. But mark, that if the golfer has not acquired the proper knack of driving--_i.e._ the proper knack of imparting just the right kind and right amount of underspin--then he will need some initial elevation in order to keep his ball in the air; and so he has to depart intentionally from the proper principles of driving, and deliberately cock up his ball, even though slightly. How his driving suffers in consequence may be gathered by taking the extreme case of no under-spin at all, upon which Professor Tait says: “When there is no rotation there must be initial elevation, and even if we make it as great as one in four, the requisite speed of projection for a carry of 250 yards would be 1120 feet per second, or about that of sound.” Now, as the actual speed of projection in the case of a fine drive by a first-class player is not more than 350 feet per second, the reader may have some idea as to how hard he would have to hit if he were dispensing with rotation. Of course “a carry of 250 yards” is extremely long, and is rarely if ever done in the absence of a helping wind from behind, but the Professor had just been speaking of the practicability of such a carry “in still air.” Even though it be abnormal, the vast disparity between an initial speed of the ball of 350 feet per second and one of 1120 feet will make the point clear. VII