during the Absorption of Electrons by Platinum. 20f> 



His value of 6, when reduced in the manner described above, 

 gives <£ = 5*63 volts. Another satisfactory set of measure- 

 ments is given by Deininger *, who finds <£ = 5*1 volts. 

 Deininger, however, seems to have used the same approximate 

 values of R and e as were used by Richardson in his first 

 paper. Using the better values of the constant e/R given 

 above, we find from Deininger's value of b that <£ = 5*26 volts. 

 Another determination to which some weight should be 

 attached is a more recent one by Richardson f. The indivi- 

 dual observations in this set are not so good as in the two 

 others, but they have the merit of comprising concordant 

 values for two different specimens of platinum. 



If we take the mean of the values given in the last 

 paragraph, assigning different weights to the different deter- 

 minations, namely 3 to Wilson's, 2 to Deininger's, and 1 to 

 Richardson's, we find <£ = 5*54 volts. This may be taken to 

 be coincident with the value 5*5 volts found ' for the corre- 

 sponding quantity in the present investigation, within the 

 limits of the errors of observation. 



Values of b for the electronic emission from hot platinum 

 in an atmosphere of hydrogen have been given by Wilson J 

 and Richardson § . These depend not only on the pressure 

 of the hydrogen, but on the previous history of the platinum 

 as well. The values given by Wilson are for a new wire 

 and are as follows : — 



Pressure of H... '0013 mm. '112 mm. 133 mm. 



Value of b 6-0 xlO 4 4*30 xlO 4 l'80xl0 4 



Value of <f> 5-16 volts 3*70 volts 1*546 volts. 



Richardson's values, which are for an old wire in hydrogen, 

 are as follows : — 



Pressure of H... 1*9 mm. 226 mm. 



Value of 6 ; 6-0 xlO 4 2*78 xlO 4 



Value of <f> 5*16 volts 2'39 volts. 



The platinum in our experiments was saturated with 

 hydrogen by electrolysis of dilute sulphuric acid and it is 

 impossible to say which of the above values our results should 

 be compared with. All the results in hydrogen have one 

 feature in common, namely that they give a smaller value of 

 <£ than that given by a platinum wire which is free from 

 hydrogen. 



* Ann. der Phys. iv. vol. xxv. p. 301 (1908). 



t Phil. Trans. A, vol. ccvii. p. 1 (1906). 



% Loc. cit. § Loc. cit. 



