432 KNOBLAUCH ON RADIANT HEAT. 



Hence it is evident that the differences which the rays of heat 

 evolved by the platinum partly at a white heat exhibit after dif- 

 fuse reflexion on transmission through diathermanous media, are 

 all greater than those which are found under similar circum- 

 stances with platinum at a yellow heat. It must consequently 

 be admitted that a still larger number of heterogeneous rays of 

 heat emanates from the former than from the latter. 



Thus the result of this entire investigation is, That the heat 

 emitted by red-hot platinum is more heterogeneous than that ema- 

 nating from this metal at a dark heat ; that from it at a yellow 

 heat more so than that when red-hot ; and that from white-hot 

 platinum more so than that which is emitted under any other 

 circumstances. 



Consequently the complexity of the heat emitted by any body, 

 as might be expected, appears greater at higher than at lower 

 degrees of temperature. 



But it neither increases in o)ie and the same body constantly 

 with the temperature, as is evident, e. g. by its remaining un- 

 changed until its temperature exceeds 234° F., nor with different 

 sources of heat, when numerous other circumstances cooperate, 

 is it always greatest with that which possesses the highest tem- 

 perature. 



Thus red-hot platinum e. g. emits more heterogeneous rays 

 than the flame of alcohol ; nevertheless it must be admitted that 

 the temperature of the former is lower than that of the latter, 

 which is capable of raising the platinum wire to either a yellow 

 or white heat. The experiments which have hitherto been made 

 show that, the differences in the nature of a source of heat have not 

 the slightest possible relation to its radiating power. However, the 

 series which the sourceswhen arranged accordingto the compound 

 nature of their rays of heat form (see p. 426, and pp. 430, 431), 

 is exactly the same as that which they would form if arranged ac- 

 cording to the varied nature of the luminous rays which they emit; 

 for we must e.^. consider the luminous rays alsoofanArgand lamp 

 as more heterOj";eneous than those of red-hot platinum, because 

 all bodies which reflect diffusely, when exposed to their influence, 

 appear to the eye of more varied colours, and the luminous rays 

 of red-hot platinum as more heterogeneous than those of the 

 flame of alcohol, because, when reflected by differently-coloured 

 bodies, they appear to the eye as far more varied than the latter. 



