KNOBLAUCH ON RADIANT HEAT. 

 11. 12. 13. 



415 



Carmine. 

 Madder-red. 

 Red woollen ta- 

 pestry. 



White velvet. 

 WTiite wool. 

 Green woollen ta- 

 pestry. 



White lead. 

 Diesbach blue. 



14. 



Black velvet. 

 Green oU-cloth. 



The following bodies cannot be referred to either of these 

 groups as regards the reflexion of heat : — 



3. It was an important question, How the alterations in heat 

 by reflexion, proved in the above manner to occur, could be ex- 

 plained. 



In regard to this point, two cases might occur. They either 

 consisted in a change of the rays of heat, which rendered them 

 more capable of permeating one or the other diathermanous sub- 

 stance, or they were the consequence of a selective absorption of 

 the reflecting surfaces for certain rays of heat transmitted to 

 them, as appeared the most probable view from the experiments 

 of Baden Powell and Melloni, 



In the first case, the differences in the reflected heat should 

 not occur until it was transmitted through the diathermanous 

 media; in the second, it must be recognizable in it, even before 

 its entrance, from the intensity with which the different rays of 

 heat would be reflected by the different surfaces, because the 

 intensity of the reflected heat is the reciprocal expression of the 

 absorption of heat (see p. 384). 



Experiment decided this point as follows : — We have learned 

 that e. (J. the heat reflected by carmine is transmitted compara- 



