118 
An Essay on the Game of Billiards. 
[April, 
still further diminished by its elevation ; so that the aim must be in the same mea- 
sure uncertain ; neither can the cue be applied in this inclined and limited direction, 
without much danger of tearing the cloth : for which reasons, this stroke is 
seldom more than an expedient, when the use of the cue is confined by the ball 
being close or near to the cushion, and the effect cannot be produced otherwise ; 
or, (if in a more open situation,) to avoid making a foul 6 one, when the interval 
between both balls is small ; for the horizontal distance, over which the point 
of the cue moves after contact, decreases, as it deviates from the horizontal line; 
that is (see Fig. 8.) if the line of impulse a, b, should be placed as c, d, it will 
reach horizontally only to c, e, a distance considerably less. This motion, with 
its causes, may be clearly exhibited in degrees of slow operation, by turning the 
ball upon the table, with a dry finger, or any other soft and rough substance ; 
but as, in playing the game, it is never designed to take place, till it hits another 
ball, the direction given should partake of that necessary for the progressive also, 
and be a composition of both, as the case may require. Here also, it is obvious 
the point must be chalked, and that the corresponding parts come into suc- 
cession as before. It may be added, when rotary motion excited by the cue, and 
the part of the ball struck, are upon the same side of a perpendicular line passing 
through the centre of the ball, it is called twisting : and when on opposite sides, 
it is denominated walking. 
In a view of this last power, or effect of power, which is the reverse of the 
former, and with which it has been in some measure contrasted ; in order to be 
more explicit, it will be necessary to revert to the part the ball rests on, from which 
the consideration of the twisting power began. In the first arc of ninety degrees, 
that is, from thence to the middle of the semicircle beforementioned, the cue 
must be held with the but-end lower than the point (see Fig. 9.), so as to impel the 
ball in a direction above its centre, which is in this case necessary to make the ball 
walk ; and being thus scarcely applicable to a very small portion of this arch, in 
the ordinary way of holding it, the power here may be considered as almost 
useless : but, in the upper arc of the semicircle, though the back-hand be some- 
what raised above that position, this impulse may be given easily, and with increas- 
ing effect, so far as about the middle of it ; and might till the cue became a tan- 
gent to the ball’s surface, (the power being as the distance between the line of 
direction and the centre of the ball,) would not the deflection of the arc be thus 
almost identified with the line of impulse, and make it impossible to prevent 
the point from slipping ; or though it should not slip, the small part exposed 
to the invading force, being instantly detached by turning under the stroke, 
while the main body lies intrenched below, and participates equally of the im- 
pression made ; the walk imparted, as well as the progressive motion, (without 
which the other is of little use,) must be very trifling. It is better, therefore, 
to strike the ball in some intermediate part of the arc, where the point will 
not be so apt to slip, or the force so quickly evaded, and a sufficient of the 
progressive may be received. The same observation may be made in playing 
for a twist, where the weight of the ball assists the chalk, and is the only differ- 
ence. 
This effect likewise branches into a division, collateral with that of twisting ; and 
may be produced by striking the ball also above the middle, but in a direction 
beyond the part whereon its rests, though below its centre, (see Fig. 10.) Here, 
too, the progressive motion is impeded by the table ; neither can the ball obey 
the impulse directly, otherwise than by passing through its surface, and it * 
a This will be fully explained hereafter, with some comments-too much at lei** 
