﻿622 On the Photoelectric Effect. 



spectrum of caesium under better conditions from the stand- 

 point of preventing fatigue. 



Previous measurements of absolute photoelectric efficiency 

 have been made by S. Werner * with sputtered films of gold, 

 platinum, silver, bismuth, and copper, and by Pohl and 

 Pringsheim t with surfaces of calcium, sodium, potassium 

 and potassium amalgams of different concentrations. For 

 a platinum film deposited in hydrogen at 0*6 mm. pressure, 

 Werner finds at v = l'36 x 10~ 15 that 1 calorie of radiation 

 liberates 5'6xl0~ 4 coulomb. The value for platinum at 

 this frequency found in the present paper is 2 x 10 ~ 5 coulomb 

 per calorie. W T erner's value is for complete absorption of 

 the radiation, whereas our value is reckoned per unit incident 

 energy of (isotropic) radiation. 



Werner also made some rough measurements of the emis- 

 sion from surfaces of ordinary (not sputtered) platinum, and 

 it appears from the data given by him that the value for 

 complete absorption by the hydrogen sputtered film re- 

 quires to be reduced by the following factors to obtain 

 the value for radiation incident on a surface of ordinary 

 platinum, viz. : — 



- on account of the reflected light ; 



- on account of the observed Greater sensitiveness of 



hydrogen films compared with films sputtered in 

 nitrogen ; and 



- on account of the greater sensitiveness of the nitrogen 



films compared with surfaces of polished platinum. 



According to these figures the total reduction factor is 

 ~ X g x ™ = tqT) I so that under the conditions of our ex- 

 periments Werner's numbers would give a sensitiveness at 

 y = l-36xl0 15 sec.- 1 of about 5'6 x 10" 6 coul./cal. This is 

 only just over one-fourth of the value given by our 

 measurements. 



The values for sodium one hour after distillation are 

 practically the same as those found by Pohl and Pringsheim 

 (17xl0~ 4 as compared with 15 — 19 x 10~ 4 coul./cal.) so 

 far as the first maximum is concerned. For values of 

 v> 10~ 15 sec. _1 the curve does not agree with their typical 

 curves but is more like that given by the figures in the last 

 column of Table I. of their paper (loc. cit. p. 176) . According 



* Ark. f. Math., Fys. o. Astr. Bd. viii. Nr. 27, Upsala (1912), Diss, 

 Upsala (1913). 



t Verh. der Deutsch. Physik. Ges. xv. Jahrgano- p. HI. p. 173 p. 431 

 {1913), 



