The scientific explanation is really a very simple one, and it was set forth very lucidly by Professor Tait. The perfect ball--using the adjective in its most absolute sense--is that which has its centre of gravity, that is to say its centre of weight, dead in the centre of the ball, the centre of measurement. It is by no means to be assumed that these two centres must necessarily coincide. For them to do so exactly is an ideal state, and while matter and man are what they are, and subject to their constant, even though slight, deviations, it is unattainable. But when a ball is properly cored and properly covered, most carefully and by the most exact machinery, the two centres come very near together, and generally, to all intents and purposes, do coincide. That they do not always do so exactly is merely because the greatest human effort is incapable of achieving the scientific ideal, and it must constantly happen that, despite all that effort, the distances between the two centres vary a little. Practically no effort can prevent it, particularly when the exigencies of circumstances demand that balls should be turned out weekly in tens of thousands, and at a price of not more than two shillings each. Now and again the separation of the centres will be greater than normal--accidental again--and then you get a really bad ball, with much bias upon it. When the centre of weight is not at centre of measurement, it means that the ball in effect is heavier on one side than the other, biassed, and that is practically equal to its being not round. Suppose you inserted a small piece of lead just inside the cover of a ball and closed it up again, shaping it as perfectly as it was before. The effect of this would be to remove the centre of weight very far towards that side, and you would have a great exaggeration of the difference between the two centres that commonly exists. If you laid that ball on a table it would promptly roll round until the weighted or biassed side were underneath. If you floated it in water it would wobble about until eventually it did the same thing; and if you floated it in air it would wobble again, and such wobbling would obviously be detrimental to its straight and even flight. There you have it. The farther the two centres are from each other--from the ideal state of absolute coincidence--the greater must be the tendency towards a wobbly or uneven flight, and diminished rotation, and consequently towards a short flight. In the case of many balls other than golf balls, these variations are very considerable. You have an extreme example when a football is out of shape, and it can be seen to make zigzags in the air. But the flight of footballs, or even cricket balls, is not such a delicate and susceptible thing as the flight of a golf ball at its far greater pace.