I860.] Draper on American Contributions to Spectrum- Analysis. 397 



series now to be considered, was published by Dr. Draper in the 

 ■ Philosophical Magazine,' May, 1847, under the title of ' The Pro- 

 duction of Light by Heat.' The chief points experimentally deter- 

 mined in it are the following : 1st, that all substances become red hot 

 at the same therm ometric degree, which is 977° Fahr. ; 2nd, that the 

 light of an incandescent solid examined by the spectroscope is con- 

 tinuous, or without lines or breaks ; 3rd, that at the same temperature 

 there is always emitted the same ray ; 4th, that as the temperature 

 rises, rays of increasing refrangibility are added, and when the 

 substance is intensely white hot all the rays of the solar spectrum are 

 present. By direct photometric measures, founded upon the principle 

 known as that of the extinction of shadows, he proved that the 

 brilliancy of the emitted light increases more rapidly than the tem- 

 perature. He also gave the true explanation of that apparent increase 

 downwards, in the less refrangible rays, which the spectroscope ex- 

 hibits at high temperatures, as depending on the physiological pecu- 

 liarities of the eye. 



It may, in passing, be remarked that a strip of platinum ignited by 

 a regulated voltaic current, was in these experiments recommended as 

 a Unit Lamp, or standard source of light and heat, in the mode that 

 has since been followed by Professor Tyndall. 



Of so much importance was this memoir considered by Melloni, 

 that he read an abstract of it, and critique upon it, before the Royal 

 Academy of Sciences at Naples. 



It is greatly to be regretted that M. Kirchhoff, in the memoir 

 he published in ' Poggendorf's Annalen,' and of which a translation 

 was printed in the ' Philosophical Magazine,' July, 1860, did not profit 

 by the example Melloni had set. On page thirteen of the last-quoted 

 work the facts that a platinum wire, as its temperature is raised, emits 

 rays of increasing refrangibility, that all bodies become red hot at the 

 same temperature, and emit special rays at special temperatures, that 

 the spectrum of an ignited platinum wire is continuous, are presented 

 as the results of his own mathematical investigation. From the 

 obscure foot-note upon that page, no reader would ever infer that all 

 these points had been proved by experiments by Dr. Draper many 

 years previously. 



III. Of Flames. — In continuation of the preceding investigation, 

 Dr. Draper published, in the ' Philosophical Magazine,' February, 1848, 

 a Memoir on " The Production of Light by Chemical Action." In 

 this, resorting, as has been subsequently continually done, to a solar 

 spectrum as the standard, and to the fixed line D, tables were pub- 

 lished of the spectra of alcohol, carbonic oxide, cyanogen burning in 

 air, cyanogen burning in oxygen, oil in air, and also in oxygen, 

 hydrogen in oxygen, nitrate of strontia, &c, as seen in the spectro- 

 scope. The convenience of reducing these flames to the yellow ray 

 D, has since been universally recognized. In like manner five such 

 tabular results of platinum ignited to different temperatures, referred 

 to the solar spectrum as a standard, had been previously published. 

 In the case of flames, the line D in these memoirs is described as 

 Brewster's yellow ray, in commemoration of Sir David Brewster's 



