262 M. Melloni on the Radiations of Incandescent Bodies, 



making the arbitraries functions of x. This would lead to 

 very complicated results, and therefore I shall not pursue the 

 subject further, but shall content myself with having added 

 another case to that treated by Mr. Boole. 



Gunthwaite Hall, near Barnsley, Yorkshire, 

 February 17, 1848. 



XXXIX. Researches on the Radiations of Incandescent Bodies, 

 and on the Elementary Colours of the Solar Spectrum. Bij 

 M. Melloni*. 



AMONG the more recent scientific publications will be 

 found a memoir by the American Professor, J. W. 

 Draper, On the Production of Light by Heatf, which appears 

 to me to merit the attentive consideration of those who interest 

 themselves in the progress of the natural sciences. The author 

 treats, in a very ingenious manner, some questions allied to 

 my own researches on light and radiant heat. In reading this 

 interesting work several ideas have presented themselves to 

 me, which I have submitted to the test of experiment. I be- 

 lieve that an analysis of the memoir of Mr. Draper, accom- 

 panied with a brief account of what I have done, will not be 

 without interest to the readers of this journal. 



Every one knows that heat, when it accumulates in bodies, 

 at last renders them incandescent ; that is to say, more or less 

 luminous and visible in the dark. Is the temperature neces- 

 sary to produce this state of incandescence always the same, 

 or does it vary with the nature of the body? In either case 

 what is its degree ? and what is the succession of coloured 

 lights emitted by a given substance, when brought to tempe- 

 ratures more and more elevated? Finally, what is the rela- 

 tion that subsists at different periods of incandescence between 

 the temperature and the quantity of light and of heat emitted 

 by a body ? 



To solve these different questions, of which some have been 

 already studied by other philosophers, Professor Draper has 

 made use of an instrument composed of a strip of platina ig- 

 nited by the action of a voltaic current. The strip was vertical, 

 its length one inch and one-third, its width the twentieth of 

 an inch, and its upper extremity being fastened to a firm sup- 

 port, it was kept stretched by a little weight furnished with a 

 copper wire, that dipped into some mercury placed in a cup 



* Read at the Royal Academy of Sciences at Naples, July 6, 1847, and 

 translated for Silliman's American Journal from the Bibliotheque U?iiver- 

 selte of Geneva for August 1847. 



t Phil. Mag., May 1847, vol. xx. p. 345. 



