392 



KNOBLAUCH ON RADIANT HEAT. 



the insertion amounted to 25°. The heat reflected by black and 

 white velvet therefore radiates through the above substances in 

 very unequal proportions ; for when the heat was reflected by 

 the former, the needle, on the insertion of the red glass, moved 

 from 13° to 8°* 16; but when the reflexion was produced by 

 black velvet, it receded from 13° to 6°*5. On inserting calca- 



Table XXIV. 



II. 



Thick- 

 ness in 

 milli- 

 metres. 



Substances inaertedc 



Deflec- 

 tion by 

 direct 

 radia- 

 tion. 



Deflection 

 after the in- 

 sertion by the 

 unreflected 

 rays of the 

 Argandlamp. 



Deflection after the 



White 

 satin. 



Black 

 satin. 



White 

 taffeta. 



Red 

 taffeta. 



1-5 



1-4 

 1-4 



4-4 

 3-7 



1-4 



Red glass 



Blue glass 

 Alum 



13° 



Rock salt . . 

 Calcareous spar 



Gypsum 



25° 



700 



519 

 .3-31 



21-69 

 13 62 



10-50 



7-54 



5-28 

 3-96 



2212 

 17 25 



1419 



7-54 



5-24 

 3-96 



2212 

 1712 



1412 



7-58 



5-28 

 413 



2212 



17-38 



1412 



7-50 



5-21 

 4-38 



22-31 

 1712 



14-12 



Corresponding results were obtained on the comparison of 

 other substances of different colours. Thus, the heat reflected 

 by white paper, which had directly deflected the needle 13°, on 

 the insertion of the red glass produced a deviation of 8°*29, that 

 reflected by black paper a deflection of 6°"12 ; and on the inser- 

 tion of the calcareous spar, the former caused the needle to 

 deviate to 19°*81, the latter to 13°-38, when the direct deflection 

 amounted to 25°. If these values be compared with those repre- 

 senting the portion of the unreflected rays which passes through 

 the red glass and the calcareous spar, 7°*46 and 14°'56, it is 

 evident that the transmission of the heat through these bodies is 



