FOOTE I LUMINOSITY AND TEMPERATURE OF METALS 



325 



which represents the luminosity of a non-black body at tem- 

 perature where 6 r is given by equation (6) . It is well known 

 that 6' is the color temperature 3 of the non-black body. 



Application of equation (8) to the determination of the melting 

 point of tungsten. Langmuir 4 found the luminosity of tungsten 

 to be 6994 candles per square centimeter at its melting point. 

 Equation (8) may be used to determine the temperature corre- 

 sponding to this value of the luminosity after the constants P, 

 A' p, and q have been evaluated. The constant P is obtained 

 by equation (2) from the work of Hyde, Cady, and Forsythe 5 

 upon the brightness of a black body at various temperatures. 

 The result of this computation is shown in the following table. 



TABLE I 



Mean P = 1.91 ± 0.05 X 10 7 



The constants p and q, on the basis of Hyde, Cady, and For- 

 sythe's 6 data for color temperature, true temperature and appar- 

 ent temperature of tungsten were found 7 to have the values 

 p = +0.0000104 and q = + 322. On the basis of c 2 = 14450 

 and these data A' = 0.303. From equation (6) 6' is found, 

 whence from equation (8) I/, the luminosity for various values 



3 Foote and Fairchild, J. Wash. Acad. Sci. 6: 195. 1916. Foote, this Journal, 

 6: 317-323. 1916. 



4 Phys. Rev. 6: 141. 1915. 



5 J. Frank. Inst. 181: 421. 1916. 



s J. Frank. Inst. 181: 419. 1916. Also Worthing, idem, p. 417. 

 7 Foote, this Journal, 6: 317-323. 1916. 



