KNOBLAUCH ON RADIANT HEAT. 



393 



reous spar, it receded in the first case from 25° to 19°'62, and 

 in the second from 25° to 15°"5. 



Similar differences were observed in other coloured surfaces 

 composed of smooth silk and velvet, as shown by the annexed 

 table, which also exhibits the relation of the transmission of the 

 reflected heat to that of the unreflected* : — 



Table XXIV. 



insertion when the heat of the Argand lamp is reflected by 



comparatively facilitated after reflexion by white paper, but im- 

 peded by that from black paper. 



The same was observed with the other diathermanous media. 

 The following table contains these differences, as also those 

 which occurred on the reflexion of the heat by other substances 

 of the same kind, of different colours : — 



* That the numbers which give the transmission of the unreflected heat 

 through the diathermanous bodies in the different tables are not the same, de- 

 pends upon their ha\ ing been observed on different days, and thus under 

 altered conditions. It would have been useless to have reduced them, because 

 the comparison of the reflecting surfaces is never extended beyond a single 

 group, within the limits of which it is of full value. 



