796 



Professor Sir J. J. Thomson 



[March 1.^, 



the reason for this rule, trace out souie of its consequences. By the 

 nose of the ball we mean the point on the ball furthest in front. 

 Thus if, as in Fig. 1, C the centre of the ball is moving horizontally 

 to the right, A will be the nose of the ball ; if it is movins; horizon- 



FlG. 1. 



tally to the left, B will be the nose. If it is moving in an inclined 

 direction C P, as in Fig. 2, then A will be the nose. 



Now let the ball have a spin on it about a horizontal axis, and 

 suppose the ball is travelling horizontally as in Fig. ;3, and that the 



Fig. 2. 



Fig. 3. 



direction of the spin is as in the figure, then the nose A of the ball is 

 moving upwards, and since by our rule the ball tries to follow its nose, 

 the ball will rise and the path of the ball will be curved as in the 

 dotted hne. If the spin on the ball, still about a horizontal axis. 



♦Fig. 4. 



were in the opposite direction as in Fig. -i, then the nose A of the 

 ball would be moving downwards, and as the ball tries to follow its 

 nose it will duck downwards, and its path will be like the dotted line 

 in Fig. 4. 



Let us now suppose that the ball is spinning about a vertical axis, 

 then if the spin is as in Fig. 5, as we look along the direction of the 



