34:2 Mr. J. H. J. Poole on a Possible Connexion between 



diminution in the total electronic current. This effect would' 

 however, be largely cut out by the following considerations. 

 Owing to local variations in the field the atoms will not set 

 themselves with their electronic orbits exactly parallel to the 

 surface, and hence, on the average, half the electrons will 

 still escape from the surface. As a large accelerating- 

 electric field was employed in my experiments, most of the 

 electrons escaping from the iron surface would be carried 

 away at once. Hence, although the initial direction of 

 emission of the electron would probably be very nearly 

 parallel to the surface, the total ionization current would 

 not be much affected. If, however, no accelerating field 

 was employed, and the iron surface was kept in a good 

 vacuum, we would expect that the maximum positive poten- 

 tial which it would attain when illuminated by light of a 

 definite wave-length, would be less when it was magnetized, 

 since in this case the component of the velocity of the 

 electron normal to the surface would be small, and therefore 

 a smaller positive potential would be sufficient to prevent 

 the electron from escaping. No experiments, however, have 

 been made on this point owing to the difficulty of obtaining 

 a sufficiently high vacuum, to insure that the mean free path 

 of the photo-electron should be at least as great as the 

 distance between the surface and. the grid. It is hoped 

 to carry out trials of this possible effect at some future 

 date. 



Fig. 1. 



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In the experiments dealt with in this paper only the 

 total ionization current from the surface was measured, and 

 hence it is only a change in the total number of electrons 

 emitted which would be detected, and not a change in the 

 direction of emission. A sketch of the arrangement used is 

 shown (fig. 1). The first experiments were made with the 



