December 22, 1910] 



NATURE 



255 



■ attery ; the upper one is electrified negatively, hence 

 '.hen one of these particles moves between the plates it is 

 exfjosed to a constant downwards force, quite analogous 

 to the weight of the ball. You see now when the particles 

 pass between the plates their path has the shape shown in 

 Fig. 16 ; this is the path of a ball without spin. I can 

 imitate the effect of spin by exposing the particles while 

 they are moving to magnetic force, for the theory of these 

 particles shows that when a magnetic force acts upon them 

 it produces a mechanical force which is at right angles 



Fig. 16. 



1 the direction of motion of the particles, at right angles 

 also to the magnetic force, and proportional to the pro- 

 duct of the velocity of the particles, the magnetic force, 

 and the sine of the angle between them. We have seen 

 that the force acting on the golf ball is at right angles 

 to the dfrection in which it is moving at right angles to 

 the axis of spin, and proportional to the product of the 

 velocity of the ball, the velocity of spin, and the sine of 



Fig. 17. 



the angle between the velocity and the axis of spin. Com- 

 paring these statements, you will see that the force on the 

 particle is of the same type as that on the golf ball if 

 the direction of the magnetic force is along the axis of 

 spin and the magnitude of the force proportional to the 

 velocity of spin, and thus if we watch the behaviour of 

 these particles when under the magnetic force we shall 

 get an indication of the behaviour of the spinning golf 



Fig. 18. 



ball. Let us first consider the effect of underspin on the 

 flight of the ball ; in this case the ball is spinning, as in 

 Fig. 3, about a horizontal axis at right angles to the 

 direction of flight. To imitate this spin I must apply a 

 horizontal magnetic force at right angles to the direction 



F.G. 19. 



of flight of the particles. I can do this by means of the 

 electromagnet. I will begin with a weak magnetic force, 

 representing a small spin. You see how the path differs 

 from the one when there was no magnetic force ; the 

 path, to begin with, is flatter, though still concave, and 

 the carry is greater than before — see Fig. 17, a. I now 

 increase the strength of the magnetic field, and you will 

 see that the carry is still further increased. Fig. 17, h. 

 1 increase the spin still further, and the initial path be- 

 comes convex instead of concave, with a still further 

 increase in carry. Fig. 18. Increasing the force still 



XO. 2147, VOL. 85] 



more, you see the particle soars to a great height, then 

 comes suddenly down, the carry now being less than in 

 the previous case (Fig. 19). This is still a familiar type 

 of the path of the golf ball. I now increase the magnetic 

 force still further, and now we get a type of flight not 

 to my knowledge ever observed in a golf ball, but which 

 would be produced if we could put on more spin than 



Fig. ;o. 



we are able to do at present. You see there is a kink in 

 the curve, and at one part of the path the particle is 

 actually travelling backwards (Fig. 20). Increasing the 

 magnetic force I get more kinks, and we have a type of 

 drive which we have to leave to future generations of 

 golfers to realise (Fig 21). 



{Fig. 21. 



By increasing the strength of the magnetic field I can 

 make the curvature so great that the particles fly back 

 behind the tee, as in Fig. 22. 



So far I have been considering underspin. Let us now 

 illustrate slicing and pulling ; in these cases the ball is 

 spinning about a vertical axis. I must therefore move 

 my electromagnet, and place it so that it produces a 

 vertical magnetic force (Fig. 23). I make the force act 



Fig. 22. 



one way, say downwards, and you see the particles curve 

 away to the light, behaving like a sliced ball. I reverse 

 the direction of the force and make it act upwards, and 

 the particles curve awav to the left, just like a pulled 

 ball. 



By increasing the magnetic force we can get slices and 



7 



Fig. 23. 

 pulls much more exuberant than even the worst we per- 

 petrate on the links. 



Though the kinks shown in Fig. 20 have never, so far 

 as I am aware, been observed on a golf links, it is quite 

 easy to produce them if we use very light balls. I have 



