1040 



The measurements. 



The pyrometer which was used for measuring the temperature 

 had been very carefully standardized at the melting-point of gold. 

 The greatest deviation in six measurements was 1° C. The active 

 wave-length of the red glass filter (Schott and Gen. N". 2745) had 

 been determined by the metliod of Hyde, Cady and Fohsythe ') 

 with a spectro-photometer. By means of photometric measurements 

 the relation was established between the current in the pyrometer- 

 lamp and the ratio of the intensity as measured at a definite tem- 

 perature through the red filter to the intensity at the melting point 

 of gold. 



The constant of the BRODHUN-photometer was determined by means 

 of a set of lamps which had been standardized in the Phys. Techn. 

 Reichsanstalt. 



The set of three prisms B C D was standardized separately. The 

 determination of the absorption of the bichromate-filter was made 

 by six observers. The results of four of these agreed to within about 

 two percent. The other two obtained larger deviations. As with 

 them similar irregularities had been noticed on a former occasion, 

 their results were rejected. 



The following results were thus arrived at; 



By means of a plot of the form log H=f(-j we found at the 



melting point of gold 7^= 1336° 77= 0,119^^A/cm"-. 



The values found by us agree well with those calculated by 

 others, but deviate very far from the numbers obtained by Nernst 

 and by Lummer and Pringsheim. It is, therefore, very probable that 

 in their measurements the Purkinje-effect must actually have played 

 a part. Nernst used rods of an area of 10 mm'. The intensity 

 in his measurements was, therefore, very small indeed. 



-) Hyde, Cady and Forsythe Astrophys Journ. (42) 294, 1915. 



