The truth is that Professor Thomson's explanation tends at the outset to confuse. The swerve of the ball has nothing whatever to do with the turning of the "nose," or the millions of noses in any particular direction apart from the extra local friction set up, as already explained, on one part of the ball.

Professor Thomson makes it very clear that he is not well acquainted with the various methods of applying spin to balls in sport. He says: "A lawn tennis player avails himself of the effect of spin when he puts 'top-spin' on his drives, i.e. hits the ball on the top, so as to make it spin about a horizontal axis, the nose of the ball traveling downwards . . . ; this makes the ball fall more quickly than it otherwise would, and thus tends to prevent it going out of court."

I have played tennis - we do not now call it lawn tennis - for more than twenty years. I am the author of four books on the game, one of which is translated into French and German, published also in America, and is recognized both in England and America as the standard work on the game, and I can assure Professor Thomson that no tennis player ever dreams of trying to get top-spin on his ball by hitting it on top. The only result would be to "founder" the ball, to drive it onto the ground before it could even touch the net, let alone get over it and into the opposite court.

HARRY VARDON Finish of Drive.

Sometimes when the bound is very high and very near the net one may hit the ball a little above the middle of its height; to use Professor Thomson's term, a little above its "nose" as seen from the opposing player's court, but even in such rare cases as these there is no attempt to hit the ball on "top." This is theory of the most unsound nature. Top-spin in tennis is obtained by hitting the ball generally speaking with a racket whose face is practically vertical and ascending in an oblique line across the intended line of flight of the ball, to put it very simply one "brushes" the racket up behind and against the ball thus gripping it and making it spring away with a lot of forward roll that is commonly called top or top-spin.

Professor Thomson indeed shows by diagram how this top-spin affects the ball, but even here he is in error. He shows the ball beginning to dip directly it is hit. It really goes quite a long way in nearly every case before the spin gets to work. Probably, almost certainly, on account of the great adhesion between the ball and the tennis racket, the ball rises after impact. It is in fact a certainty that most balls hit with top-spin do so rise for a majority of them are hit below the height of the net.

Professor Tait makes this error in his article Long Driving, and it is quite clear to me that Professor Thomson is following him very closely in his statements.

Here is a statement by Professor Thomson about the soundness of which many of my readers will be better able to judge than I am: "Excellent examples of the effect of spin on the flight of a ball in the air are afforded in the game of base-ball. An expert pitcher, by putting on the proper spin, can make the ball curve either to the right or the left, upwards or downwards; for the sideway curves the spin must be about a vertical axis; for the upward or downward ones, about a horizontal axis."

I speak here, subject to correction, but I should imagine that all good pitchers tilt the axis of spin out of the vertical and so get gravitation in as an ally instead of fighting it by keeping the plane of spin horizontal. We get much greater swerve in the American service at tennis, where the axis of spin is tilted over, than we do in services where we keep the axis of spin nearly vertical.

Professor Thomson says: "If a ball were spinning about an axis along the line of flight, the axis of spin would pass through the nose of the ball, and the spin would not affect the motion of the nose; the ball, following its nose, would thus move on without deviation."

The spin which Professor Thomson is here describing is that which a rifle bullet has during its flight for it is obvious that a rifle bullet is spinning "about an axis along the line of flight" and that the axis of spin does pass through the nose of the bullet. We know, however, that in the case of the rifle bullet there is a considerable amount of deviation, which is called "drift," and not swerve. This has never been very clearly explained although some most learned treatises have been written about it.

It is, of course, an impossibility to communicate this spin to a golf ball by means of a golf club, but reasoning from the analogy of the rifle bullet I cannot see that Professor Thomson is safe in so dogmatically asserting that there would be no deviation. In fact, I am inclined to think that if tempted I might show that a golf ball with a similar spin to the rifle bullet would deviate from its course.

I have just said that it is impossible to produce this spin with a golf club. The question naturally arises how could one make the test. I believe it could be done with a straight hit ball provided the ball was grooved in curves of such a nature that the wind would be almost sure to engage them and so turn the ball until it acquired a certain amount of spin.

I saw a sample of such a ball some time ago. It had four to six poles and the lines were all in curves flowing one way. The idea was ingenious but the resulting patterns would not be popular with golfers; and while the ball might hold its flight well, in plain hit balls it would not, I think, have any advantage in the important class of balls hit with backspin, for it would naturally have a constant tendency to fight across the plane of spin of the backspin.

Professor Thomson performed some most elaborate experiments to prove the truth of those things which Newton explained about two hundred and fifty years ago and which were recognized as fundamental truths until I was rash enough to use them in London, when they were called my "theories." They never really understood how complimentary they were.