JOURNAL 



OF THE 



WASHINGTON ACADEMY OF SCIENCES 



Vol. III. APRIL 4, 1913 No. 7 



PHYSICS. — The constants of spectral radiation of a uniformly 

 heated enclosure. W. W. Coblentz, Bureau of Standards. 



In a previous communication to this Journal a general descrip- 

 tion was given of the work^ which was completed prior to Decem- 

 ber, 1912. It was then proposed to observe several more sets of 

 energy curves, at the highest operable temperatures with a 

 vacuum furnace before publishing the exact numerical results. 

 Owing to unavoidable delays in assembling all the apparatus, the 

 intention of witholding all the data until the completion of this 

 investigation has now been abandoned and in the present paper is 

 given a brief summary of the most reliable data now at hand. 



The temperature scale used in this investigation, for tempera- 

 ture above 1400°C is the optical scale, which is obtained by adding 

 to the thermoelectric temperatures certain values,^ which are the 

 mean of several groups of thermocouples. In assembling the 

 present data for publication it was observed that for tempera- 

 tures above 1400°C there was an abrupt rise in the value of the 

 constant c which increased systematically to abnormally high 

 values for temperatures taken above 1500°. It was therefore 

 necessary to choose between the possibility that (1) this variation 

 in c at high temperature is owing to the failure of Planck's law at 

 high temperatures or (2) that, for the particular thermocouples 



1 Coblentz, Jour. Wash. Acad. Sci., 3: 10, 1913. ' 



2 Waidner and Burgess, Bull. Bur. Standards 3: 205, 1907. 



177 



