While he was at work on these reckonings he dispelled one fallacy,
which, notwithstanding, is commonly held by golfers to the present day.
Most players think that when driving and following through well the ball
hangs on the face of the club, as it were, for long enough for the club
to do something in the way of guiding it. How brief is the time in which
the actual stroke is made for good or ill was proved conclusively in a
very striking manner, and that time was set down--the whole time of
impact--as that in which the club, moving at 300 feet a second, passed
through about four times the linear space by which the side of the ball
was flattened. Putting this space down, nowadays, at about ⅛ in., and
reckoning the time that it would take the club going at the speed
indicated to cover that small distance, we have the fact that the
duration of impact is only about 1/7000th of a second, and that that is
the whole time that the golfer has for the guiding of the ball! As the
Professor said, “the ball has, in fact, left the club behind before it
has been moved through more than a fraction of its diameter”; and in the
case of the gutta, with the smaller extent to which it flattened on the
club, he came to the conclusion that the duration of impact was far less
than that which has just been mentioned.
Incidentally in this connection he took occasion to expose another of
the golfer’s fallacies as to the effect of wind on the flight of the
ball, in the following words: “It is well to call attention to a
singularly erroneous notion very prevalent among golfers, namely, that
a following wind carries a ball onwards! Such an idea is, of course,
altogether absurd, except in the extremely improbable case of wind
moving faster than the initial speed of the ball. The true way of
regarding matters of this kind is to remember that there is always
resistance while there is relative motion of the ball and the air, and
that it is less as that relative motion is smaller, so that it is
reduced throughout the path (of flight) when there is a following wind.
Another erroneous idea somewhat akin to this is that a ball rises
considerably higher when driven against the wind, and lower if with the
wind, than it would if there were no wind. The difference (whether it is
in excess or deficit will depend on the circumstances of projection,
notably on the spin) is in general very small; the often large apparent
rise or fall being due mainly to perspective as the vertex of the path
is brought considerably nearer to or farther from the player.”
And Professor Tait was led to make a definite pronouncement on the
particular kind of weather in which a ball will fly best and farthest.
What golfers do not generally realise is that the atmospheric resistance
to the flight of their ball is much greater than in simple proportion to
its speed; it is as the square of the speed. This is to say, that if one
ball is driven twice as fast as another to begin with, the resistance to
that ball is four times as great as it is to the slower one. It is this
fact which makes it so difficult to get extra length, beyond a good
length, on to a ball, no matter what improvements are made in the ball.
Therefore, on the weather question the Professor set it down that, “Of
course, other circumstances being the same, the only direct effect is on
the co-efficient of resistance. If this be taken as proportional
(roughly) to the density of the air, it may vary, in this climate, to
somewhere about 10 per cent. of its greatest value, and the drive is
accordingly shortest on a dry, cold winter day with an exceptionally
high barometer. The longest drive will, of course, be when the air is as
warm and moist as possible, and the barometer very low.”
But he probed most deeply into the mysteries of the flight of the golf
ball when he came suddenly to understand the rotation which was
subjected to it by the club, and it is of interest and importance to
every golfer that he should understand it also. The starting-point of
the wonderful investigations that he made is contained first in the
simple fact that when an object is poised in the air there is equal
atmospheric pressure upon it at all points; and second, that, as several
of the most eminent scientists before him, from Newton onwards, had
found out, when a sphere rotates in a current of air the side of the
sphere which is advancing to meet the current is subject to greater
pressure than is that which is moving in the direction of the current;
and a step further in this argument is that, as the result of this extra
pressure, if a spherical ball be rotating, and at the same time
advancing in still air, it will deviate from a straight path in the same
direction as that in which its front side is being carried by the
rotation.
Therefore, when a ball is sliced, it is made to spin round so that its
front side moves round constantly to the right, and, in accordance with
the law just mentioned, there is a greater atmospheric pressure on the
left side than on the right, and, consequently, the ball is pushed away
to the right--as we see it. When it is pulled, the spin is in the
opposite direction, and the extra pressure is from the right, and so it
is sent away to the left. When the ball is topped the spin on the front
side is downwards, and the ball ducks--the extra pressure this time
being in the same direction as gravity; and when under-cut is applied,
and under-spin follows, the front side of the ball is spinning upwards,
and the extra pressure is from below and against gravity.
When this conclusion was first briefly stated, golfers resisted the
suggestion that when driving they imparted any under-spin to the ball;
but the Professor stuck to his point, and proved it beyond doubt, and it
is in this way that the ball takes six and a half seconds over its
flight instead of the three and a half that it would otherwise do; and
he proved, moreover, that if there was no under-spin imparted to it when
driving it would only travel about half the distance that it usually
does. The greater the under-spin the greater the upward pressure, and
this conclusion leads to others very interesting.