36 THE RADIATIONS OF IGNITED BODIES. [MEMOIR I. 



In view of the foregoing facts, I conclude that as the 

 temperature of an incandescent body rises, it emits rays of 

 light of an increasing ref Tangibility, and that the appar- 

 ent departure from this law, discovered by an accurate 

 prismatic analysis, is due to the special action of the eye 

 in performing the function of vision. And as the lumi- 

 nous effects are undoubtedly owing to a vibratory move- 

 ment executed by the molecules of the platinum, it seems 

 from the foregoing facts to follow that the frequency of 

 those vibrations increases with the temperature. 



In this observation I am led by the principle that " to 

 a particular color there ever belongs a particular wave- 

 length, and to a particular wave-length there ever be- 

 longs a particular color;" but in the analysis of the spec- 

 trum made by Sir D. Brewster by the aid of absorption 

 media, this principle is indirectly controverted, that emi- 

 nent philosopher showing that red, yellow, blue, and con- 

 sequently white light, exist in every part of the spectrum. 

 This must necessarily take place when a prism which 

 has a refracting face of considerable magnitude is used ; 

 for it is obvious that a ray falling near the edge and one 

 falling near the back, after dispersion, will depict their 

 several spectra on the screen ; the colors of the one not 

 coinciding with, but overlapping the colors of the other. 

 In such a spectrum there must undoubtedly be a general 

 commixture of the rays ; but may we not fairly inquire, 

 whether, if an elementary prism were used, the same facts 

 would hold good ; or if the anterior face of the prism 

 were covered by a screen, so as to expose a narrow fis- 

 sure parallel to the axis of the instrument, would there 

 be found in the spectrum it gave every color in every 

 part, as in Sir David Brewster's original experiment? 

 M. Melloni has shown how this very consideration com- 

 plicates the phenomena of radiant heat; and it would 

 seem a very plausible suggestion tha-t the effect here 



