CHAPTER VI
ON THE ROTATION OF BALLS
The subject of this chapter is a very difficult one to deal with in a manner at all satisfactory, and the writer is conscious that the want of minute knowledge, both theoretical and experimental, must render the task before him formidable in every way. Yet there is no intention of evading it, for the remarks which will be offered for consideration are based on a lengthened observation of the behaviour of billiard balls under various conditions, and will, it is believed, prove of interest, if not of use, some to one person, others to another, even though put forward in an unscientific manner.
In most books on billiards the subject is avoided; a chapter (of a page or two) is devoted to side, and those writers who have dealt with it most briefly have probably made the fewest mistakes. An exception, however, must be made in the case of M. Vignaux, in whose ‘Manual’ endeavour is made, with considerable success, to explain many phenomena in a homely way; and as the observations and deductions therein recorded often agree with those arrived at in this book independently, it is not remarkable that the courage which the Professor has shown in attempting a difficult subject should be admired, and that the skill which has led him to no small measure of success should be praised. Besides, in trying to convey instruction the teacher is much assisted, and the learner finds his task more easy, in proportion as the reasons for orders are understood. A rule whereby a player is desired to use right-hand side for a certain stroke from baulk to the top of the table, and left-hand side for a similar stroke from the top to baulk may be perfectly correct; but it is much more likely to be remembered and put in practice at the moment of need if the reason why has been explained and is known. Hence, some space will be devoted to the consideration of rotation, and it may be that when attention is drawn to the various effects, or some of them, due to this cause, a better qualified writer may be induced to study and deal with the subject in a more scientific and satisfactory manner. If this should happen, the remarks now made, however imperfect and conjectural, will not have been thrown away.
It has already been brought to the reader’s notice that a ball, when set in motion by the stroke of a cue, does not merely slide forward, but at once commences to rotate round its horizontal axis, which is at right angles to the axis of the cue, or the path of the ball. That is, in addition to the movement of displacement, or movement from one place to another (which can be effected by taking the ball in one’s fingers and placing it down in its second position), called by the French ‘translation,’ there is generated a distinct movement of rotation, which is for the most part latent and invisible till after impact with another ball or with a cushion.
That the motions are distinct is evident; for a ball or a cube may be so pushed or removed from one spot on the surface of the table to another that no rotation results. Again, the same ball may be made to spin or rotate by the action of the fingers, and dropped vertically on the table, so that no impulse forwards or backwards is communicated, and yet no sooner does the ball fall on the cloth than it will commence to travel in a line at right angles to the axis of its rotation. Hence, both motions may produce displacement or translation, and when both are at the same time active in a ball the path travelled, whether straight or curved, is the resultant of the two movements.
In Or Out Of Baulk?
Now at p. [132]–3 the divisions of balls were explained, and the same figure will suffice to assist in defining the various classes of rotation used in the game of billiards to effect different purposes at the discretion of the player. There are four main divisions, corresponding to the four sectors into which the lines H B and G D divide the ball.
(1) Forward rotation, or follow, is communicated by striking the ball on the line C H above the centre C.
