1898.] on Magneto-Optic Rotation. 721 



of vibration must have different frequencies for the same velocity 

 of propagation. 



The vibrations of the molecules of a gas in which the Zeeman 

 effect is produced by a magnetic field may be represented by the 

 motion of a pendulum the bob of which contains a rapidly rotating 

 gyrostat with its axis in the direction of the supporting wire of the 

 pendulum. The period of revolution of the bob when moving as a 

 conical pendulum is greater or less than the period when the gyrostat 

 is not sj^inning according as the direction of revolution is against or 

 with the direction of rotation. 



The bob when deflected and let go moves in a path which 

 constantly changes its direction, so that if a point attached to the bob 

 writes the path on a piece of paper, a star-shaped figure is obtained. 

 I cause the gyrostatic pendulum here suspended to draw its path by 

 a stream of white sand on the blackboard placed below it, and you 

 see the result. 



I must here leave the subject, and may venture to express the 

 hope that on some other occasion some one more specially acquainted 

 with the electromagnetic aspects of the phenomenon may be induced 

 to place the latest results of that theory before you. 



[A.G.] 



