Speaking roughly, billiard balls may be taken as measuring two inches in diameter, which means that the centre is one inch from the circumference and that the part midway between the centre and the circumference is at a distance of half-an-inch from each.
From a half-ball stroke, as everyone who handles a cue knows, aim has to be taken at the edge of the object ball; for a plain three-quarter-ball stroke, aim has to be taken exactly midway between the edge and the centre of the object ball, and for a quarter-ball stroke aim has to be taken the same distance away from the edge-or half-an-inch in either case. These three principal aims-at the edge, half-an-inch inside the edge, and half-an-inch wide of the edge, account for, probably, 75 per cent. of the strokes that have to be made in billiards. Another valuable thing to know and remember is that the same pocket or cannon stroke, so far as the run of the cue ball is concerned, is made whether three-quarter or quarter-ball aim be taken.
In the half-ball stroke, in which aim is taken at the edge of the object ball, the red ball is struck half-an-inch from its edge; in the three-quarter ball stroke it is struck three-quarters of an inch from its edge; and in the quarter-ball stroke it is struck a quarter-of-an-inch from its edge. In the half-ball stroke, the two balls travel at the same pace after contact, but in the three-quarter ball stroke the red takes on more pace than the white and in the quarter ball stroke less. Thus in the fuller than half-ball strokes the cue ball loses pace, which the object ball gains, and in finer than half-ball strokes the cue ball takes on extra pace whilst the object ball lags.
The result of ordinary, and especially of heavy, cueing at short range is what is called a "stun" shot-an excellent stroke in its proper place but a disastrous one when not intended. For some little distance after being centrally struck, the cue ball slides along the cloth without revolving; and this sliding action is increased by grasping or pinching the cue. If the cue ball comes into contact with the object ball before rotation has fully set in it takes a wider angle than usual, and this can only be obviated by high and light cueing At longer range, the high- cueing is not essential, as natural rotation sets in, but the lightly-held cue will be found to work magic in almost every stroke that is made in billiards.
The run of the object ball should always be mentally forecasted before the immediate pocket or cannon is made, otherwise the position for the next stroke becomes a matter of chance, as does also the avoidance of a kissing of the balls, or of the unintended loss of the object ball in a pocket, in baulk, or under a cushion. Exactly what is meant here will be quickly appreciated if the object ball be placed 24 inches above the baulk central spot, with the cue ball on one of the baulk corner spots. This is a plain half-ball stroke into either of the middle pockets and if placed exactly half-ball and with correct strength will bring the object ball back into the same position from off the top cushion. This particular shot is now becoming known as the "Gray" shot, although it is one that has long been familiar to, and practised by, all position players.
All that a player desiring favourable after position for the object ball after any half-ball stroke has to remember is that the half-ball contact is always midway between the edge and centre and that the ball will travel along an imaginary line drawn through it from that exact point. Similarly, in three-quarter ball strokes the line of travel would be from a contact point three-quarters of an inch from the edge of the object ball and in quarter ball strokes from a contact point one quarter of an inch from the edge of such ball. If the rapid observation thus taken reveals the fact that the intended half-ball, three-quarter ball, or quarter-ball stroke would drive the object ball in an undesirable or risky direction a different class of stroke must be made, even though the chance of bringing off the immediate shot be thereby jeopardized.
We have already seen that, in making a half-ball in-off stroke, aim is taken at the edge of the object ball, and that the point of contact is midway between the edge and centre of the object ball. Consequently whenever an imaginary line drawn from this midway point of contact would reach the most open part of a pocket the pot is a half-ball one. The same thing applies to three-quarter and quarter ball pots. When the imaginary line from the pocket comes out three-quarters of an inch from the edge (or a quarter of an inch from the centre) aim must be taken midway between centre and edge and when the line comes out a quarter of an inch from the edge aim must be taken half-an-inch finer than the edge.
To sum up what has been said as to the principal aims and contacts for in-off strokes and as to the run of the object ball in each case, we find that For a half-ball in-off stroke, aim is taken at the edge of the object ball and contact takes place half an inch inside the edge. In a half-ball in-off stroke, the object ball, being struck half an inch inside its edge, travels along an imaginary line drawn through its diameter from that point.
For a three-quarter ball in-off stroke, aim is taken half an inch inside the edge of the object ball and contact takes place three-quarters of an inch inside the edge (or a quarter of an inch from the centre).
In a three-quarter ball in-off stroke, the object ball, being struck three-quarters of an inch inside its edge (or a quarter of an inch from the centre), travels along an imaginary line drawn through its diameter from that point.
For a quarter ball in-off stroke, aim is taken half an inch outside the edge of the object ball and contact takes place a quarter of an inch inside the edge.
In a quarter ball in-off stroke, the object ball, being struck a quarter of an inch from its edge, travels along an imaginary line drawn through its diameter at that point.
To sum up what has been said as to principal aims and contacts for "pot" strokes and the throw off of the cue ball in each case, we find that A half-ball pot stroke is on when an imaginary line from the most open part of the pocket comes out at a point half an inch from the edge of the object ball.
The cue ball in such a stroke is aimed at the edge of the object ball and takes the usual half-ball direction.
A three-quarter ball pot stroke is on when an imaginary line from the most open part of the pocket comes out at a point three- quarters of an inch from the edge (or a quarter of an inch from the centre) of the object ball.
The cue ball in such a stroke is aimed half an inch inside the edge of the object ball and takes the usual three-quarter ball direction.
A quarter-ball pot is on when an imaginary line from the most open part of the pocket comes out at a point a quarter of an inch from the edge of the object ball.
The cue ball in such a stroke is aimed at a point half an inch outside the edge of the object ball and takes the usual quarter- ball direction.