404 PROCEEDINGS OF THE AMERICAN ACADEMY. 



netic field serves as a rectifier, and when a Leyden jar is used it allows 

 only the oscillation from the cathode to reach the focal plane. 



The canal rays appear to fatigue certain substances, — for instance, 

 lithium chloride and rubidium chloride, — and after the application of 

 these rays the blue phosphorescence of the cathode rays is diminished. 

 It can, however, be restored by increasing the strength of the cathode 

 beam. This can be accomplished by the following arrangement. A 

 storage battery was connected to the exhausted tube through a large 

 running water resistance, and a spark gap was inserted in the circuit. 

 The coatings of a small Leyden jar were connected to the spark gap ; 

 the spark seemed continuous to the eye. Under the effect of the 

 longitudinal magnetic field a very brilliant phosphorescence could be 

 produced even after extreme fatigue of the group lithium, caesium, and 

 rubidium chlorides. It is therefore probable that the cathode phos- 

 phorescence can be restored by stronger and stronger cathode rays 

 condensed in the manner I have described. 



Jefferson Physical Laboi;atory, 

 Harvard University. 



