CH. v.] OF LENARD RAYS 53 



Fig. 5 shows Lenard's apparatus for showing that 

 his rays are accelerated or retarded by passing along 

 the lines in an electric field between two disks ab. 

 Here C is the cathode of a Lenard tube similar to 

 that shown in fig. 1, and the rays enter an 

 aluminium window at A, thence passing on through 

 an earthed tube n leading to one of the charged 

 disks. The disks are perforated to allow the rays to 

 pass through them ; they go on through another tube 



TO EARTH 



FIG. 5. Lenard's apparatus for exhibiting the effect of a longitudinal 

 electric field in affecting the velocity of cathode or Lenard rays. 



m, which, with the disks, is kept at high potential, and 

 thence between the plates de, which represent either 

 an electric or a magnetic field ; after which they 

 encounter a phosphorescent screen S, and depict upon 

 it a luminous spot. The observation consists in 

 observing the change of position of this spot when 

 the sign of the electrification of the plates ab is 

 changed ; for if the longitudinal field alters the 

 velocity, the deflexion caused by the field de will 

 also be modified, and thereby the change in velocity 

 is demonstrated. 



