Proceedings of the Royal Institution, 



381 



tiling distinct from heat, and that its radiation was affected by sur- 

 face precisely like heat. For it is evident, that the hypothesis of M. 

 Prevost will not of itself explain these facts. If all bodies, whethet 

 hot or cold, radiate heat, and if their different effects be ascribabfe 

 only to the different intensities of their radiation,, it is obvious, that, 

 by weakening the radiating power of a comparatively cold body, we 

 should increase its cooling influence ; and that the bright ice-col^ 

 canister ought to depress the thermometer more than the black one, 

 because the former radiates less of that feeble heat which M. Pre- 

 vost's theory supposes to emanate from both. 



This is the point which is not cleared up in any English work ; — 

 the objection which these experiments offer to the hypothesis of M. 

 Prevost is only in appearance ; and it was reserved for M. Fourier 

 to point out that M. Prevost's ideas were perfectly consistent with all 

 the observed phenomena. But to do this, it is necessary to remem- 

 ber, that surface influences the re/lection of heat in a manner directly 

 the reverse of its effect upon radiation ; that is to say, a briglit me- 

 tallic surface reflects about ten times as much heat as one that is 

 rough and blackened. When this circumstance is combined with the 

 other considerations, it will be evident, that Mr. Leslie's experiments 

 suggest no difficulty, but that they are in fact perfectly reconcileable 

 with each other, ^d with the theory of M. Prevost, as the annexed 



diagram will explain. 



Here the mirrors may be omitted, as in fact they merely oomp|ir 

 cate the question, without at all assisting in its solution. Let a a and 

 APRIL— JUNE, 1830. 2 C 



