428 



KNOBLAUCH ON RADIANT HEAT. 



the experiments on the heated cylinder, always })asses through 

 the diathermanous substances used for testing it, whether unre- 

 flected or diffusely reflected by the most dissimilar bodies. Thus 

 in all these cases, on inserting the red glass a deflection of 

 8°'08 to 8°*25 was obtained ; on inserting the calcareous spar, of 



When the heat of red-hot platinum, is reflected by the same 

 bodies, as we know, very distinct differences occur on trans- 

 mission. Thus e. g. the unreflected heat on transmission through 

 red glass produces a deflection of 10°*42 ; that reflected by black 

 paper, of 9°'58 ; that reflected by carmine, of 12°'33 ; and that 

 portion of the unreflected heat which is transmitted by calcareous 



Table LIII. 



After these results there can be no doubt that the heat emitted 

 by red-hot platinum is more heterogeneous than that evolved by 

 this metal at a dark heat. 



When the heat of platinum at a yellow heat is diffusely re- 

 flected by the above surfaces, these differences become still 

 greater. Thus, whilst the unreflected heat which permeates the 

 red glass deflects the needle 8°*83, that reflected by black paper 

 causes it to deviate 7°*42 ; that emitted by carmine, to 10°*58 ; 

 and the unreflected heat, when transmitted by calcareous spar, 



