The flight of the ball, and particularly of the golf ball, exercises a strange fascination for many people to whom the phenomena of flight exhibited by a spinning ball travelling through the air, are not of the slightest practical importance. That is to say, there is an immense number of people who take merely a scientific, and one might almost say an artistic interest in the effects produced by the combined influence of spin and propulsion. Scientific men have been for many years well aware of the causes which produce the swerve of a ball in the air. By swerve I mean, of course, a curve in the flight of the ball which is due to other causes than gravitation, and in the word swerve I do not include the drift of a ball which has been perfectly cleanly hit, but which, in the course of its carry, has been influenced by a cross wind. This does not legitimately come under the heading of swerve. It is more correctly described as drift, and will be dealt with in due course.

In the Badminton Magazine of March 1896, the late Professor Tait published an article on "Long Driving." Professor Tait was a practical golfer and a very learned and scientific man. He proved most clearly that a golf ball could not be driven beyond a certain distance. He proved this absolutely and conclusively by mathematics, but, so the story runs, his son, the famous Freddie Tait, proved next day with his driver, that his father's calculations were entirely wrong, for he is alleged to have driven a golf ball over thirty yards farther than the limit which his learned parent had shown to be obtainable. Naturally, Professor Tait had to reconsider his statements, and he then arrived at the conclusion that there must have been in the drive of his son, which had upset his calculations, some force which he had not taken into consideration. He soon came to the conclusion that this was back-spin, and he dealt with this matter of back-spin, which is a matter of extreme importance to golf, in a most erudite article, which is much too advanced for the ordinary golfer, so I shall content myself here with referring to just a few of the most important points in connection with it. It is necessary that I should, in dealing with the flight of the ball, give those of my readers who are not already acquainted with the simple principles of swerve, some idea of what it is which causes the spinning ball to leave the line of flight that it would have taken if it had been driven practically without spin.

The explanation is very simple. If a ball is proceeding through the air, and spinning, the side which is spinning towards the hole gets more friction than the other side which is spinning away from the hole. It is well known that a projectile seeks the line of least resistance in its passage through the air. It follows that the greater friction on the forward spinning half causes the ball to edge over towards the side which is spinning away from the hole. This, in a very few words, is the whole secret of swerve.

Professor Tait stated in his article that Newton was well aware of this fact some 230 years before the publication of the professor's article, and that he remarked when speaking of a spinning tennis ball with a circular as well as a progressive motion communicated to it by the stroke, "that the parts on that side where the motions conspire must press and beat the contiguous air more violently, and there excite a reluctancy and reaction of the air proportionately greater."

This really is an extremely simple matter and a very simple explanation. I have taken care to explain it so simply, for swerve is, by a very great number of people, looked upon as an abstruse problem - in fact, my book on Swerve, or the Flight of the Ball, is catalogued as a treatise on applied mathematics, instead of, as I intended it to be, simply a practical application of the ascertained facts to the behaviour of the ball in the air.

Professor Tait's article has enjoyed a wonderful vogue. Although it was published nearly twenty years ago it is quite frequently quoted at the present time. There are, however, in it some errors which one would not have expected to have found in such a scientific article. Speaking of the golf ball shortly after it has left the club, Professor Tait said:

It has a definite speed, in a definite direction, and it may have also a definite amount of rotation about some definite axis. The existence of rotation is manifested at once by the strange effects it produces on the curvature of the path so that the ball may skew to right or left; soar upwards as if in defiance of gravity, or plunge headlong downwards instead of slowly and reluctantly yielding to that steady and persistent pull.

There is, in this statement of Professor Tait's, a fundamental error in so far as regards the flight of the ball. He said: "The existence of rotation is manifested at once by the strange effects it produces on the curvature of the path." This is incorrect from a scientific point of view, and it is also badly stated. The existence of rotation is not manifested "at once"; in very many cases, practically in all, the ball proceeds for quite a long distance before the effect of rotation is seen. This is more particularly so when it is a matter of back-spin, but it is equally true of the pulled ball or the sliced ball. Both of these proceed for a considerable distance before the effect of spin is noticeable. In fact it is well known to all golfers that the spin begins to get to work as the velocity of the ball decreases. Also it seems as though it is incorrect to refer to the strange effects it (rotation) produces on the curvature of the path, for it is the rotation itself which produces the curvature.

Professor Tait then said:

The most cursory observation shows that a ball is hardly ever sent on its course without some spin, so that we may take the fact for granted, even if we cannot fully explain the mode of its production. And the main object of this article is to show that long carry essentially involves under-spin.