To the Editor.
In your last issue you publish, under the above heading, a letter from me which I wrote in response to your request for correspondence on the subject.
In a foot-note to the letter you remark that "Col. Western does not say in his book that a seven-eighths ball is a grazing ball." As I neither accused him of doing so nor so defined it myself, your comment was evidently made under a misapprehension.
I fully endorse your opinion as to the value of Col. Western's book, but on this question of aims he merely reverses the old naming of the finer and fuller than halfball aims, and I still submit that the old way is the better.
Up to the present we have directed our one-eighth, quarter and three-eighths ball aims to points in space; Col. Western does the same thing for his five-eighths, three-quarter, and seven-eighths aims.
It appears to me more consistent to have a thick contact by a three-quarter aim than the thin one which Col. Western's method gives.
On page 3 in reply to question 122 you say that the objective point "is always (except in full ball strokes) just twice as far from the centre of the object ball as the desired point of contact." Permit me with all deference to point out that this is quite a fallacy, although it is frequently mentioned.
For instance, the contact of a half-ball aim is not at a spot on the circumference of the object ball midway between the point aimed at and the point cut by an imaginary line connecting the centres of the cue and object balls. The contact is nearer the latter point and, of course, its position varies according to the distance between the balls.
A. LONG BROWN.
Muswell Hill, N.
March 25, 1912.
To the Editor.
In last month's Billiard Monthly you say:— Tests revealed clearly the fact that bonzoline balls are less elastic than crystalates, that crystalates are less elastic than hard (or African) ivory balls, and that soft (or "Indian") ivory balls are the most elastic of all.
Among various definitions of elasticity, perhaps the following from Chambers's Encyclopaedia is as good as any:— Elasticity is that property of matter which enables a body, whose form or bulk has been changed by a force to support without disintegration or further yielding the continued action of that force, and to recover its original form or bulk when left to itself.
When the cue ball strikes the object ball, a very slight flattening of both balls is the immediate result, at the point of contact. I will assume the force is not sufficient to break the balls, or crack them, or injure them in any way.
Then immediately the elasticity of the balls comes into play.
They tend to, and do, recover their original form, and the more effectively and the more rapidly they recover their original form, or shape, or sphericity, after the temporary slight flattening at the point, the more elastic they are, and the more effectively and rapidly they recover shape, the wider the angle at which the cue ball will be thrown off.
Play with two balls of some acknowledged inelastic substance such as clay, or lead. You will find the throw off of the cue ball less than that of Indian ivory. We must make the experiment of course with the same contact, or angle, say a true half-ball stroke, and you will find that the less elastic the substance, the less the throw-off, i.e., the less wide the angle of the cue ball. And so I think on investigation you will find that the greater the elasticity the greater the throw-off.
The greatest throw-off is with bonzoline, so I should say the most elastic balls are bonzoline and the less elastic are crystalate, and the still less elastic are ivory.
Your paragraph suggests that your view is that the less the throw-off, the greater the elasticity. My view is that the greater the throw-off, or the wider the angle, the greater the elasticity. May I say without offence to your "professional billiard expert" that he probably knows more about practical billiards than he knows about the theory of elasticity.
Another definition of elasticity from "Ganot's Physics" is:—
Elasticity is the property in virtue of which bodies resume their original form or volume when the force which altered that form or volume ceases to act.
But your paragraph puts it the other way and I venture to think it is wrong.
H. C. W.