Why? The Science of Athletics

280 WHY?-THE SCIENCE OF ATHLETICS If the discus is thrown properly it will rotate round its own centre of gravity and will fly with a perfect scale, but should it not be given enough "spin" in the final propulsive effort it will soon commence to change its rate of rotation _and ·will "wobble", owing to instability in flight. To make this matter plain, Fig. 102 has been drawB. ·FIG. 102 This figure shows three positions of a discus in flight that has been projected inefficiently. This is plain from the fact that the centres of rotation of the missile along the line ab do not correspon.d with the centre of gravity, which passes through the centrally placed screw that fastens the two faces of the discus together. The constant changing of the centre of rotation and its non-coincidence with the centre of .gravity makes the discus unstable in flight. The above theory was propounded as long ago as 1913 in my book Success in Athletics, a book in which I col– laborated with the late Major R. V. Mostyn and Dr. T. J. PryceJenkins. This led, I am told, to experimental research concerning the science of discus throwing. During the last twenty-odd years we have learned something, but far from all, about certain of the elements and forces involved in the flight of a discus, and the results of these forces measured in distances of throws . The impossibility. of measuring the reactions of the discus to extraneous forces while it is free in air must