Electrons hy Metals under Influence of Alpha Rar/s. 475 



on the case is increased, more and more of these electrons 

 are withheld from reaching the brass plate. The fact that 

 this radiation communicates a positive charge to the plate is 

 not an obstacle to the hypothesis that it consists of electrons. 



Fig. 4. 



Since the early experiments of Lenard it has been known 

 that electrons, moving with velocities corresponding to several 

 hundred volts, when they fall upon a metal, cause the latter 

 to emit secondary electrons, which may carry 



a larger 



