V.] CONDITION )!' 111H SUN'S SURFACE. . s ;, 



" Whence, applying the same proposition to other 

 1 indies, it follows that all bodies, when their tempera- 

 ture is gradually raised, begin to emit waves of the same 

 length at the same temperature," etc. (Draper, Phil. 

 Mag., Vol. XXX., p. 345. Berl., 1847.) 



"For the same temperature the magnitude (I) is a 

 continuous function of the wave-length, except for such 

 values of the latter as render (I) evanescent. The truth 

 of this assertion may be concluded from the continuity 

 of the spectrum of a red-hot platinum wire, provided it 

 be admitted that the power of absorption of such a body 

 is a continuous function of the length of the waves of 

 the incident rays." 



These, together with other facts, were presented by M. 

 Kirchoff, not as experimental, but as mathematical results. 

 No allusion was made to the fact that the whole subject 

 had been extensively investigated, as shown in the pre- 

 ceding pages, many years before, the only reference to 

 such investigation being; that contained, as shown above, 



O O ' 



in a parenthesis, which in the original is in a foot-note, 

 and even this was omitted in an historical memoir on the 

 subject shortly afterwards published by M. Kirchoff. 



As an example of the effect of this, I may quote from 

 the Cours de Physique de FJZcole Poly technique, of Paris, 

 by Professor Jamin : 



"M. Kirchoff has deduced the following important 

 consequences : 



" Black bodies begin to emit at 977 Fahr. red radia- 

 tions, to which are added successively and continuously 

 other rays of increasing refrangibility as the temperature 

 rises. 



" All substances begin to be red-hot at the same tem- 

 perature in the same enclosure. 



" The spectrum of solids and liquids contains no fixed 

 lines." 



