COBLENTZ: NOTE ON COEFFICIENT OF RADIATION 1 85 



RADIATION. — Note on the coefficient of total radiation of a 

 tmiformly heated enclosure. W. W. Coblentz, Bureau 

 of Standards. 



Under the above title the writer pubhshed^ a value of the 

 so-called vStefan-Boltzmann constant of radiation from a uni- 

 formly heated enclosure or so-called black body. The value 

 is 0- = 5.72 X 10-'- =t 0.012 watt cm"'- deg~^ It is based 

 upon about 600 measurements, made with 10 receivers, which 

 are summarized in table 6 of a previous publication.- The data 

 obtained with receivers nos. 8 and 9 were not included because 

 the apparatus was defective. The data obtained with these 

 10 receivers were corrected for radiation lost by reflection, 

 which loss amounts to 1.2 per cent for receivers covered with 

 lampblack (soot) and 1.7 per cent for receivers covered with 

 platinum black. It does not include a set of measurements 

 made on an unblackened radiator. The reflection from a re- 

 ceiver covered with platinum black, then smoked, is 1.2 per 

 cent. These corrections were determined by direct measure- 

 ments upon some of the receivers and by comparison of the sur- 

 faces of the other receivers with samples of lampblack whose 

 reflection losses had been determined in a previous investiga- 

 tion.'' 



Experiments were made on atmospheric absorption and it 

 was shown that if any correction to these data for atmospheric 

 absorption is to be made, it can hardly be greater than o.i per 

 cent. 



Recently a new determination' of this radiation constant was 

 brought to my attention, and in view of the fact that this paper 

 contains inaccurate statements concerning my own work a 

 few comments are permissible. For example, the statement 

 is made that the only novelty in the apparatus employed by 

 Coblentz and Emerson {loc. cit.) was a thermopile with a contin- 

 uous receiving surface, which is of secondary importance. As a 



' Proc. Nat. Acad. Sci, 3: 504. 191 7. 



- Coblentz and Emerson. Bull. Bur. vStand. 12: 549. 19 16. 



» Bull. Bur. Stand. 9: 283. 1913- 



* Kahanowicz. Nuovo Cimento (6) 13: 142. 1917. 



