Electrons emitted in Photo- Electric Effects. 105 



results obtained were consistent, as was to be expected. It 

 is clear that the ratio of the selective effect to the normal 

 increases slowly as the accelerating potential decreases. In 

 other words, the electrons in the selective effect tend to 

 follow the electric field somewhat more readily than those in 

 the normal effect. The results are plotted in fig. 4. The 



Fig. 4. 



• 







^ 



^S' 













r 







itf* 











/ 











#at/b-§. 









/ 



















f 



















ZOO 

 volts 



250 



curve for the selective effect has practically become flat 

 with 404 volts, showing that all the electrons' emitted from 

 the alloy, whatever be their direction of emission, have been 

 received by the electrode E. It is unfortunate that acceler- 

 ating potentials greater than 404 volts could not be used in 

 order to find where the normal curve became flat. We may, 

 however, estimate that the normal curve becomes flat at 

 about 500 volts. It is worthy of note that by multiplying 

 the coordinates of the normal curve by suitable factors, the 

 normal curve can be brought into close coincidence with 

 the selective curve. 



These experiments show that there is a small difference in 

 the way in which the electrons are emitted in the two effects, 

 although it is quite small in comparison with the difference 

 in the order of magnitude of the two effects. Is this 

 difference due to a difference in the velocity with which the 

 electrons are emitted, or to a difference in the direction in 



Phil. Mag. S. 6. Vol. 31. No. 182. Feb. 1916. I 



