And Professor Tait was led to make a definite pronouncement on the particular kind of weather in which a ball will fly best and farthest. What golfers do not generally realise is that the atmospheric resistance to the flight of their ball is much greater than in simple proportion to its speed; it is as the square of the speed. This is to say, that if one ball is driven twice as fast as another to begin with, the resistance to that ball is four times as great as it is to the slower one. It is this fact which makes it so difficult to get extra length, beyond a good length, on to a ball, no matter what improvements are made in the ball. Therefore, on the weather question the Professor set it down that, “Of course, other circumstances being the same, the only direct effect is on the co-efficient of resistance. If this be taken as proportional (roughly) to the density of the air, it may vary, in this climate, to somewhere about 10 per cent. of its greatest value, and the drive is accordingly shortest on a dry, cold winter day with an exceptionally high barometer. The longest drive will, of course, be when the air is as warm and moist as possible, and the barometer very low.” But he probed most deeply into the mysteries of the flight of the golf ball when he came suddenly to understand the rotation which was subjected to it by the club, and it is of interest and importance to every golfer that he should understand it also. The starting-point of the wonderful investigations that he made is contained first in the simple fact that when an object is poised in the air there is equal atmospheric pressure upon it at all points; and second, that, as several of the most eminent scientists before him, from Newton onwards, had found out, when a sphere rotates in a current of air the side of the sphere which is advancing to meet the current is subject to greater pressure than is that which is moving in the direction of the current; and a step further in this argument is that, as the result of this extra pressure, if a spherical ball be rotating, and at the same time advancing in still air, it will deviate from a straight path in the same direction as that in which its front side is being carried by the rotation.