56 Mr. Powell on Light and Heat 



bution among the primary rays when analyzed by a prism. But 

 the conclusion once maintained of an absolute separation of heat- 

 ing rays by this means, has been more recently shewn to be most 

 probably owing to red rays of so deep a colour as not to be ordi- 

 narily visible. (See Mr. HerscheVs Paper ^ Edinh. Trans. 1823, 



§• 7.) 



And though the recent experiments of Dr. Seebeck have 

 shewn that this heat is distributed to different j^arts of the spec- 

 trum in very different degrees, according to the different nature of 

 the prism employed, yet since the light is known to be also simi- 

 larly affected, this is no proof of the distinct existence of separate 

 rays of heat. 



Upon the whole, then, we must view these effects as due to a 

 certain power or property of communicating heat belonging to the 

 rays of light. But this need by no means involve the supposition 

 that light and heat are identical, or can be converted the one into 

 the other. But with respect to this view of the subject, we may 

 obtain greater certainty by returning to the subject of the forego- 

 ing experiments. 



14. At the commencement of this inquiry I viewed it as bearing 

 upon the theory, which asserts that the radiant matter from lumi- 

 nous sources is of one species, only gradually changed from heat 

 into light. The facts here established so far disprove this opinion, 

 that we evidently perceive a very considerable portion of the ra- 

 diant matter undergoing no change whatever, except an increase 

 in intensity. 



If, therefore, we still adhere to the supposition that light is only 

 heat in a different state, we must so far modify the hypothesis as 

 to admit that only a part of the igneous fluid undergoes this 

 change. 



15. But without assuming any hypothesis, it is evident that the 

 total effect, whether communicated directly, or by means of the 

 light, must have originated in some way from the hot body; and 

 although I have proved the total effect to be distinguishable into 

 two parts or species, we still cannot consider them otherwise than 

 as both derived from the same Bource. I conceive it already suf- 



