46 THE RADIATIONS OF IGNITED BODIES. [MEMOIR I. 



radiant heat, read before the Royal Academy of Sciences 

 at Naples a memoir entitled "Researches on the Radi- 

 ations of Incandescent Bodies and on the Elementary 

 Colors of the Solar Spectrum." This was translated into 

 French from the Italian, and published in the BilMo- 

 tlieque Universelle of Geneva. It was also translated into 

 English, and published both in England and America. 



M. Melloni commences his memoir as follows : " Among 

 the more recent scientific publications will be found a 

 memoir by the American professor J. W. Draper ' On the 

 Production of Light by Heat,' 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 pre- 

 sented themselves to me, which I have submitted to the 

 test of experiment. I believe that an analysis of the 

 memoir of M. Draper, accompanied with a brief account 

 of what I have done, will not be without interest. 



"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 necessary to produce this state of incandes- 

 cence 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 colored lights emitted by a given sub- 

 stance when brought to temperatures more and more ele- 

 vated? Finally, what is the relation that subsists at 

 different periods of incandescence between the tempera- 

 ture and the quantity of light and of heat emitted by a 

 body?" 



Melloni then describes the apparatus and the processes 

 I had used to determine the thermometric degree of in- 

 candescence and its uniformity for different substances. 



