Why? The Science of Athletics

282 WHY?-THE SCIENCE OF ATHLETICS ground were identical and consistent from the point of delivery, although the angle of the missile to the resultant wind was continually changing. This, it is suggested, may be due to the spin of the discus on its own axis having a gyroscopically stabilizing effect, which helps to prevent any large alteration in the ~ initial angle of inclination. Pictures taken from the rear (the discus being painted half black and half white) further established the theories of more than twenty years ago, for it was found that the discus in flight made from r8 to 21 complete revolutions; or enough to steady the flight, although not enough in aerodynamic effect to otherwise increase the distance thrown. Further, the experiments produced a Drag, Lift component of three forces besides gravity, and Momentum which is constant. These forces were "drag" , "lift" and "momentum". In this connection it must be remembered that whether the discus is moving forward against still air, or air in motion, the character of the force is the same, although the strength of the force varies. Moreover, an object moving forward tends to create a vacuum, and the shape of the discus is such that a partial vacuum is created behind and on top of the missile, when it is thrown at an angle upward from the horizontal and less than the vertical ; and consequently the discus is being constantly pushed up into its partial vacuum by the pressure resulting from its own motion and from whatever wind may be blowing against its flight. This is the "lift", already referred to, which helps the discus to overcome the force of gravity and causes it to progress with what is known, in athletic parlance, as "a true scale". 'The best "scale" is seen when the discus is flying through still air, or against the wind. The firs't inference would appear to be, therefore, that the stronger the head– wind the higher the discus will mount and the further it will fly ; but this is only true in part, for there is bound to come a point at which the strength of the head-wind