liU 



KNOWLEDGE 



[J AX. 



1882. 



uhrniists. Even so late as; 1874 it furnished to the 

 (Jormiin exi>crini('nt<TS the basis of a very interesting dis- 

 cussion in |)iiotoihc'iiiistiy. 



"In 18 fj Dr. Draper discovered that not only might 

 the Fraunliofer fixed lines in the spectrum lie photo- 

 ■,'raplicd, 1)ut that there exist.s a vast number of others 

 lii'yond the violet, which up to that time had been un- 

 known. He also found three great lines less refrangible- 

 than the red, in a region altogether ii.\isiblc to the eye. 

 Of the.se new linos, which more than doubled in number 

 those of Fraunhofcr, he published engravinirs. Ifo ;dso 



the stars, and the nebulae. In this paper he established 

 experimentally that all solid substances, and probably 

 liquids, become incandescent at the same temp«'ra- 

 ture ; that the thermometric point at which such 

 substances are red-hot is about 'J77' Fahr. ; that the 

 spectrum of an incandescent solid is continuous, it contain.^ 

 neither bright nor dark fixed lines ; and from common 

 temperatures up to 977° Fahr. the rays emitted by a solid 

 are invisible, but at that temperature they impress the eye 

 with the .sensation of red ; that the heat of the incandescing 

 body bi -in 2 made continuously to ri.se, other rays are added. 



PR. J. W. DRAPER. 



invented an instrument for measuring the chemical force 

 of light — the chlor-hydrogen photometer. This was subse- 

 (luently extensively used by Bunsen and Koscoe in their 

 photo-chemical researches. In their paper, read before the 

 Royal Society in 18.56, they say, 'With this instrument 

 Draper succeeded in establishing experimentally some of 

 the most important relations of the chemical action of 



" His memoir ' On the Production of Light by Heat,' 

 published in 1847, was an important contribution to 

 spectrum analysis. Among other things it gave the means 

 for determining the solid or gaseous condition of the sun. 



increasing in refraugibility as the temperature ascends ; 

 and that, while the addition of rays so much the more re- 

 frangil>le as the temperatiire is higher is taking place, there 

 is an augmentation in the intensity of those already 

 existing. This memoir was published in both American 

 and European journals. An analysis of it was read 

 in Italian before the Koyal Academy at Naples, 

 July, 1847, by Melloni, which was also translated 

 into French and English. But, thirteen years s<dise- 

 quently, M. Kirchhotl" published, in a very celebrated 

 memoir, considered by many as the origin of spectrum 

 analysis, and of which an English translation may be 



