4 " N n RAYS 



Now, without altering the position of the 

 gap, turn it so that it comes parallel to OZ, i.e. 

 normal to the cathode rays. The influence of 

 the " X " rays on the spark is then seen to 

 disappear, and the interposition of a lead or 

 glass plate causes no change in its brightness. 



"X " rays have therefore a plane of action, 

 which is the one passing through each "X" 

 ray and the cathode ray which gives rise to it. 

 If the direction given to the spark-gap is inter- 

 mediate between the two above mentioned, the 

 action is seen to diminish from the horizontal 

 position to the vertical. 



The following is another experiment, still 

 more striking: if the spark is made to turn 

 about OX, parallel to plane YOZ, the spark is 

 seen to pass from a maximum brightness when 

 horizontal to a minimum when vertical. These 

 variations of brightness are similar to those 

 observed when a pencil of polarized rays tra- 

 verses a rotating Nicol's prism, the small spark 

 playing the part of analyzer. The pencil of 

 "X" rays presents the same asymmetry 

 as a pencil of polarized light. According to 

 Newton's definition, it has sides differing from 



