THE VISIBLE RADIATION FROM CARBON.* 

 By Edward L. Nichols. 



Presented May 8, 1901. Received Jlay 15, 1901. 



The law of radiation has for a long time been considered by physicists 

 as a subject of high interest, and numerous investigations looking to the 

 establishment of a general relation between radiation and temperature 

 have been made both from the theoretical and the experimental stand- 

 point. The earliest attempts to determine incandescence in its relation 

 to temperature were made with platinum. Draper f in 1847 made 

 observations upon a wire of that metal heated by an electric current. 

 The temperatures were determined from the expansion of the wire. 

 Zollner$ in 1859 compared the light emitted by incandescent platinum 

 with the heat evolved. E. Bec(iuerel,§ who made an extensive study of 

 vi.-iible radiation from various solids at high temperatures, used thermo- 

 elements of platinum and palladium, calibrated by refei-ence to melting 

 points with the air thermometer. A partial separation of the rays was 

 effected by means of colored screens. 



Becquerel found that opaque bodies, such as lime, magnesia, platinum, 

 and carbon, at the same temperature had very nearly equal emissi\:e 

 powers, a conclusion vigorously contested by his contemporaries, but ex- 

 plained, in the light of later work, by the fact that the flowing bodies 

 were enclosed in a long earthen tube. The conditions for ideal blackness 

 were thus approximately fulfilled. He likewise made photometric obser- 

 vations upon wires electrically heated and found the liglit to increase 

 much more rapidly than the emitted heat. 



Although some of Becquerel's results were at fault, particularly his 

 estimation of temperature above the melting point of gold, his work is 

 especially notewortliy in that he employed many of the methods to which, 



* An investigation carried on in part by means of an appropriation from the 

 RuniforJ Fund. Read at the meeting of the Anierioan Association for the Advance- 

 ment of Science in New York, June 27, 1900. 



t Draper, Philosophical Magazine, XXX. 345 (1847). 



J Zrdlner, Pliotometrische Untersuchungen (18.59). 



§ Becquerel, Annales de Cliimie et de Physique, {■)), LXVIII. 47 (1803). 



