NICHOLS. — THE VISIBLE RADIATION FROM CARBON. 7o 



candescent lamp. He found that the first light to appear was not that of 

 the region nearest the red end of the spectrum, but corresponded in wave 

 length to the region of maximum luminosity, and that at these low tem- 

 peratures the spectrum was devoid of color. Stenger * in the same year 

 corroborated Weber's observations and offered what has since been 

 received as the proper explanation of the phenomenon. 



In 1889 I published in collaboration with W. S. Franklin f a series of 

 spectrometric comparisons of incandescent lamps maintained at various 

 degrees of brightness. No attempt was made to determine temperatures. 

 In 1891 H. F. Weber I read a paper at the Electrotechnical Congress 

 in Frankfurt on the general theory of the glow-lamp. By means of 

 numerous measurements through a wide range of incandescence made 

 upon lamps with treated and untreated filaments, constants were estab- 

 lished for his empirical formula for the relation of radiation and tempera- 

 ture. 



The infra-red spectrum of carbon has, since the appearance of the 

 incandescent lamp, likewise been subjected to measurement. Abney and 

 Festing § in 1883 published curves for the distribution of energy in the 

 spectrum of such lamps from measurements made with the thermopile. 

 In 1894 I compared, with the help of the same in-itrument and a highly 

 sensitive galvanometer, the infra-red spectra of lamps with black and gray 

 filaments. || 



Of late years attention has been devoted especially to the problem of 

 the law of radiation from an ideal black body, and various formulae have 

 been proposed by means of which the rise of radiation of any single wave 

 length upon the one hand, and of the total radiation on the other, may be 

 expressed as a function of the temperature. Interesting as this phase of 

 the problem is from the point of view of theoretical physics, it is perhaps 

 even more important to know the relation between temperature and 

 radiation for actual surfaces. 



Apparatus and Outline of Method. 



I propose in the present paper to describe an attempt to measure the 

 temperature of carbon rods rendered incandescent by the passage of an 



* Stenger, Wiedemann's Annalen, XXXIL 271 (1887). 



t Nichols and Franklin, Am. Jour, of Science, XXXVIII. 100 (1880). 

 ' t Weber, Bericht des internationalen Elektrotechniker-congresses zu Frankfurt 

 am Main, p. 49 (1891) ; also Physical Review, IL 112. 



§ Abney & Festing, Pliilosophical Magazine, (5) XVI. 224 (18.33); also Pro- 

 ceedings of the Royal Society, XXXVII. 157 (1884). 



II Nichols, Physical Review, II 260 (1894). 



