322 



foote: temperature and emissivity 



Color temperature of platinum. Koenigsberger has determined* 

 the emissivity for various wave lengths in the visible spectrum 

 for platinum at room temperature. If the logarithm of the 

 emissivity is plotted against 1/X the slope of the straight line is 

 Cop, whence p of equation (1) is directly determined. This com- 

 putation gives p = 0.0000287. Waidner and Burgess 7 deter- 

 mined the emissivity of platinum at its melting point (assuming 

 melting point = 1 755 °C.) for three different wave lengths. Their 

 values give p = 0.0000185. It is quite possible that this latter 

 value of p is too low because of the difficulty in obtaining accu- 

 rate measurements of emissivity at high temperatures. If both 

 values of p are correct platinum must have a temperature coeffi- 

 cient of emissivity and the temperature coefficient must be a 

 function of the wave length. The following table shows the 

 relation between the color temperature and the true temperature 

 of platinum, based on both values of p. 



TABLE IV 



•Ann. d. Physik, 43: 1205-22. 



7 Bur. Stds. Sci. Paper No. 11, p. 244. 1905. 



