74 PROCEEDINGS OF THE AMERICAN ACADEMY. 



iti the hands of later investigators, our knowledge of the laws of incan- 

 descence is due. He established the direct proportionality of the loga- 

 rithm of the intensity of radiation to the temperature and pointed out the 

 possibility of optical pyrometry. 



In 1878 Crova* used the Glan spectrophotometer in the comparison 

 of various sources of light, such as candles, gas flames, the lime light, the 

 arc light, and sunlight, and proposed au optical method for the measure- 

 ment of temperatures. 



In 1879 f I published the results of a series of measurements made in 

 this manner upon the visible radiation from platinum at various tempera- 

 tures. At that time, the measurement of high temperatures by means 

 of thermo-elements, of platinum and platinum-rhodium, or platinum-ind- 

 ium, had not been developed, aud j the determination of the temperature 

 from the change of resistance of the metal was, as has been previously 

 pointed out by Siemens, a matter of great uncertainty on account of the 

 varying performance of different samples of platinum. This difficulty, 

 which was due to the impurities contained in the metal, has since been 

 largely overcome, and platinum thermometry has, through the study of 

 Callendar and others, been advanced to the position of au operation of 

 precision, but at that time I was forced to content myself in the investi- 

 gation just referred to with an expression of temperature of the glowing 

 platinum in terms of its increase of length. 



Work upon the incandescence of carbon was first taken up in a serious 

 manner after the development of the incandescent lamp. 



Schneebeli,$ in 1884, made some observations upon the total radiation 

 and candle power of the Swan lamp. He made no estimation of tem- 

 peratures. 



In the same year Schumann § published his very complete spectro- 

 photometric comparison of the various incandescent lamps in use in 

 Germany. Lucas, || in 1885, heated arc-light carbons in vacuo, estimated 

 their temperature from the current employed, and measured the light 

 given in carcels. I shall refer to his work in some detail later. 



In 1887 H. F. Weber U began his studies of the spectrum of the in- 



* Crova, Comptes Rendus, LVII. 497 (1878). 



t Nichols, Ueber das von gliihendem Platin ausgestrahlte Licht. Gottingen, 

 1879 ; also American Journal of Science, XVIII. 446 (1879). 

 t Schneebeli, Wiedemann's Annalen, XXII. 430 (1884). 

 § Schumann, Elektrotechnische Zeitschrift, V. 220 (1884). 

 || Lucas, Comptes Rendus, C. 1451 (1885). 

 IT Weber, Wiedemann's Annalen, XXXII. 256 (1887;. 



