foote: total emissivity and resistivity 



Figure 1 represents the total emissivity of platinum as a func- 

 tion of the temperature in the range 0° to 1700°C. 



The computed points are represented by crosses. Prelimi- 

 nary observations made with radiation pyrometers which were 

 later found to be somewhat defective are shown by small dots 

 and the final observations made with an instrument compara- 

 tively free from these defects are plotted as circles. The large 

 dot at 15°C. was obtained from the work of Hagen and Rubens 

 on the reflection coefficients of platinum. These investigators 

 have determined the dispersion of the reflection coefficient to 



Temperature °C 



Fig. 1 



25/1. If the values of Ex = 1 — Rx are substituted in equation 

 (6) the total emissivity may be btained. The integration was 

 performed graphically. The triangles represent the observations 

 of Lummer and Kurlbaum.^° 



The agreement between the theoretical and experimental 

 values is excellent, when one considers the difficulties involved 

 in an accurate determination of total emissivity. The devia- 

 tions of the computed values from the observed values are in 

 general much less than ± 0.01, which is about the limit of ac- 

 curacy of the experimental determinations. 



Table I presents a summary of the values of the total emis- 

 sivity of pure platinum for the temperature range 0° to 1700°C. 



10 Lummer and Kurlbaum, Verb. d. Phys. Ges., 17: 106. 1898. 



