MI.M..IU I.J Till. KADIATIONS OF IGNITED BO1MI S. 47 



Hi- dwells on the fact that melted metals, such as lead, 

 have the same point of ignition. He agrees in excepting 

 tin- phenomena of phosphorescence, and those in which 

 light is developed in chemical combinations. He re- 

 marks that "some philosophers of the highest eminence, 

 among them M. Biot, suppose that the first light disen- 

 gaged by incandescent bodies is blue, and they have ac- 

 counted for this on the principle of a theory now univer- 

 sally abandoned. But these cases," he adds, "ought to 

 be carefully distinguished from incandescence properly 

 speaking, which arises directly and solely from an eleva- 

 tion of temperature in the body, and which always com- 

 mences with a red light. 



" As to the exact degree of this temperature, the ob- 

 jections which might be raised against the mode em- 

 ployed by M. Draper are of very little importance. If 

 we compare the results at which he arrives with those 

 that have been obtained by Wedgwood and Daniel, the 

 difference is only 30 in excess in the first case, and 3 too 

 little in the second. The differences are much greater 

 when compared with the deductions of Davy and Sir I. 

 Newton, which gave 812 and 635, respectively. But 

 those numbers, and especially the latter, were obtained 

 by methods too imperfect to be trustworthy. Conse- 

 quently the number 977 Fahr., given by M. Draper, 

 must approach very closely the degree of heat which 

 produces the first incandescence of bodies." 



Melloni then describes the method I had resorted to 

 for investigating the nature of the colors which are de- 

 veloped by an ignited body as its temperature is in- 

 creased. 



He dwells on the employment of a reference spectrum, 

 which was resorted to in consequence of the spectrum of 

 a solid having no fixed lines a discovery which has 

 become of the utmost value in astronomical spectrum 



