418 COBLENTZ: BLACK BODY RADIATION 



PHYSICS. — Constants of spectral radiation of a uniformly heated 

 inclosure or so-called black body, II? W. W. Coblentz, 

 Bureau of Standards. 



A knowledge of the exact value of the constants which enter 

 into the mathematical equation which represents the distribu- 

 tion of energy in the spectrum of a black body is necessary in 

 many physical problems, especially in extending the tempera- 

 ture scale higher than is possible by means of thermocouples. 



Spectral energy curves have been obtained by means of a 

 vacuum bolometer, a mirror spectrometer, and a fluorite prism; 

 and the constants of spectral radiation of a black body have 

 been published in a previous paper. 2 



The present paper gives the result of a recomputation of 

 these constants. This recomputation was necessitated by the 

 adoption of a new and apparently more reliable calibration curve 

 of the fluorite prism used in the work, and by the discovery of 

 a small error which was found in the previous computations. 

 Although these errors are small (and would have been considered 

 negligible four years ago) they happen to be of the same sign 

 and, hence, have an appreciable effect upon the final result. 



The results of the present computations give a mean value 

 of C = 14369, which is close to the mean value of all the published 

 data. 



When the data of other investigators are summarized, it is 

 found that they lie close to C = 14350. 



From a consideration of the data now available it appears 

 that the values of the constants of spectral radiation are close to 



C = 14350 micron deg. 

 A = 2890 micron deg. 



and that the coefficient of total radiation is of the order of <r = 

 5.7 X 10~ 12 watt cm. -2 deg. -4 . This indicates that the con- 

 stant h of the quantum theory is of the order h = 6.56 to 6.57 

 X 10~ 27 erg sec. 



1 Detailed paper to appear as Bur. Stds. Sci. Paper No. 284 (Bull. Bur. Stds., 

 13: 459-477). 1916. 



2 Bur. Stds. Sci. Paper No. 204 (Bull. Bur. Stds., 10: 1-77). 1913. 



