Complete Photoelectric Emission. 153 



light. From these numbers Partzsch and Hallwachs** 

 have calculated that for gold a = l*03xl0 6 cm." 1 and 

 /3 = 0'59 x 10 6 cm.~ 1 , Since gold and platinum do not differ 

 much from one another in atomic weight and density, the 

 value of the electron absorption coefficient a will almost 

 certainly be much the same for both metals. Meier's katoptric 

 measurements with gold at wave-length \ = 2'57 x 10 -5 give 

 numbers which lead to /3 = 0"56x 10 6 cm. -1 , in satisfactory 

 agreement with that deduced from Rubens and Ladenburg's 

 observation. The absorption coefficient for platinum in this 

 part of the spectrum is larger than that for gold in the ratio 

 1*65 to 1*14 according to Meier ; so that in dealing with 

 platinum the value of fi should be increased to 0*85 x 10 6 cm." 1 

 instead of 059 x 10 6 cm. -1 . In this way we estimate the 

 value of f a H- /3) /a over the part of the spectrum which is 

 photoelectrically active to be 



(a + £)/«= 1-82 (6) 



In arriving at the value of the complete photoelectric 



emission from platinum at 2000° K. the product v ,, J N 



<l-p) 



has been taken outside the integral in (5) and the foregoing 



average values substituted in it. This is not exact, but it 



is the best that can be done with the data at present available, 



and in any event it is accurate enough for the immediate 



purposes of these calculations. The remaining integral 



\ (1 — p)^-y^ — Y v — dv has then been evaluated graphically, 



using the values of (1— p) j^ € given by the measurements 



of Oompton and Richardsonf and Richardson and Rogers"):. 



It is not claimed that the results of these calculations give 

 more than a, rough idea of the magnitude of the complete 

 photoelectric emission. For one thing, the absolute value 

 of the photoelectric emission when measured under a given 

 illumination varies considerably with the state of the metal 

 surface, and in a manner which cannot be said fully to be 

 understood. In the second place, a number of approximate 

 or doubtful assumptions are involved in the calculations. Of 



* Ann. der Physik, vol. xli. p. 269 (1913). 

 t Phil. Mag. vol. xxvi. p. 549 (1913). 

 \ Loc. cit. 



Phil. Maq. S. 6. Vol. 31. No. 182. Feb. .1916. M 



