1910] 0)1 the Dynamics of a Golf Ball. 799 



one way when the spin is in one direction, and in the opposite way 

 when the direction of spin is reversed. The beam, as vou will see, 

 rotates in the same direction as the cylinder, which an inspection of 

 Fig. 8 will show you is just what it would do if the cylinder were acted 

 upon by a force in the direction in which its nose (which, in this case, is 



Air Blast 



Fig. 8. 



the point on the cyhnder first struck by the blast) is moving. If I stop 

 the blast, the beam does not move even though I spin the cylindei', 

 nor does it move when the blast is in action if the rotation of the 

 cylinder is stopped ; thus both spin of the cylinder and movement of 

 it through the au- are required to develop the force on the cylinder. 



Fig. 9. 



Another way of showing the existence of this force is to take a 

 pendulum whose bob is a cylinder, or some other symmetrical body, 

 mounted so that it can be set in rapid rotation about a vertical axis. 

 When the bob of the pendulum is not spinning the pendulum keeps 

 swinging in one plane, but when the bob is set spinning the plane in 

 which the pendulum swings no longer remains stationary, but rotates 

 slowly in the same sense as the bob is spinning (Fig. 9). 



Vol. XIX. (No. 104) 3 & 



