8 JV. F. Holmaii 



turned to its original magnitude. The same explanation, how- 

 ever, may be given by assuming a migration of electrons with the 

 negative current, and the possibility of appreciably changing their 

 available number in the metal in the same way as the quantity of 

 hydrogen is changed. 



A repetition of the above experiments with several different 

 metals brought to light an entirely different set of influences. 

 With electrodes freshly polished the electrode chamber was left 

 at extreme vacuum in connection with the dryer for several 

 hours, after which the photo-electric current was tested as before 

 in an atmosphere of less than .001 mm. pressure. The mean re- 

 sults of a number of tests, in which the individual observations 

 revealed about the same fluctuation in value as those in the pre- 

 vious experiments, are given in table V. In this series the ca- 

 pacity. C. was about 2.800 cm., other conditions as before. 



Table V 



A striking feature in these results is the exceptionally large 

 value of the photo-electric current of zinc as compared with the 

 previous tests — the magnitude in one case being as much as 

 seven times as high as the largest values before, and in no case 

 dropping as low as the maximum value previously obtained. In 

 these experiments it is to be noted that after use as cathode the 

 current is greatest, and after standing in hydrogen or used as 

 anode it is generally considerably smaller, the dift'erent metals 



132 



