JOURNAL 



OF THE 



WASHINGTON ACADEMY OF SCIENCES 



Vol. VI JUNE 4, 1916 No. 11 



PHYSICS. — The relation between color temperature, apparent tem- 

 perature, true temperature, and monochromatic emissivity of 

 radiating materials. Paul D. Foote, Bureau of Standards. 



In an earlier note 1 the relation between color temperature and 

 true temperature was discussed. The present paper interrelates 

 the color temperature, apparent temperature, true temperature, 

 and monochromatic emissivity coefficient of a radiating mate- 

 rial. A new method of determining the temperature coefficient 

 of monochromatic emissivity is also considered. 



Most metals are supposed to have practically zero tempera- 

 ture coefficient of monochromatic emissivity in the visible spec- 

 trum, a region of resonance where the well known Maxwell rela- 

 tions for emission coefficient do not apply. This supposition is 

 not thoroughly warranted by experimental data, since the accu- 

 racy of many of the data is not sufficient to detect a 10 per 

 cent change in emissivity over a temperature range of several 

 hundred degrees. For some metals, moreoever, a small tempera- 

 ture coefficient of monochromatic emissivity has been observed. 

 The following empirical equation may represent the emissivity 

 for wave lengths in the visible spectrum and a moderate tem- 

 perature range where A', c», p and q are constants, A the emis- 

 sivity coefficient, T the absolute true temperature, and X the 

 wave length in microns. 



1 Foote and Fairchild, J. Wash. Acad. Sci. 6: 193-197. 1916. In this paper 

 the following corrections were overlooked in the manuscript. Eq. (3), change 



+ — to — — , page 195, Eq (5) and lines 10 and 14, change +p to —p. 



A A 



317 



