THE 

 LONDON, EDINBURGH and DUBLIN 



PHILOSOPHICAL MAGAZINE 



AND 



JOURNAL OF SCIENCE. 



— , ♦ 



[FOURTH SERIES.] 

 SEPTEMBER 1860. 



XX. On the Radiative Powers of Bodies with regard to the 

 Dark or Heat-producing Rays of the Spectrum, By Balfour 

 Stewart, M.A* 



1. TN their communication which appeared in the August 

 -*- Number of this Magazine, Professors Kirchhoff and 

 Bunsen have furnished us with some very interesting and 

 important facts regarding the spectra of different kinds of flame : 

 the following is one of these : — 



" It appears," they say (while describing the effect produced 

 upon flame-spectra by the presence of small quantities of metals 

 or bodies containing metals), " that the alteration of the bodies 

 with which the metals employed were combined, the variety in 

 the nature of the chemical processes occurring in the several 

 flames, and the wide differences of temperature which these 

 flames exhibit, produce no effect upon the position of the bright 

 lines in the spectrum which are characteristic of each metal" 



2. Now when the particles of the body which mingle with 

 and characterize the flame are exceedingly divided, we may with 

 much probability (as far as the quality of the radiated light is 

 concerned) regard them as ultimate particles or molecules : the 

 spectra exhibited will then afford us the means of approximately 

 ascertaining what kind of light the molecules of certain sub- 

 stances give out when heated. It thus appears that we have 

 grounds for supposing that the ultimate particles of different 

 substances which possess in common some characterizing metallic 

 element, give out the same quality of light when introduced into 

 flame. 



3. It becomes interesting to know if we have any means of 

 detecting a similar property of bodies (should such exist) having 



* Communicated by the Author. 

 Phil Mag. S. 4. Vol. 20. No. 132. Sept. 1860. N 



