422 KNOBLAUCH ON RADIANT HEAT. 



When these results are compared with those which were ob- 

 tained on the transmission of the heat diffusely reflected by the 

 above bodies through diathermanous substances, it appears — 



1 . That a surface which reflects heat in such a manner that it 

 is transmitted by red glass, blue glass, alum, rock salt, calca- 

 reous spar and gypsum in a greater degree than that reflected 

 by any other, in comparison with the latter, reflects the heat of 

 the Argand lamp best, that of red-hot platinum next, that of the 

 flame of alcohol in a less degree, and that of the heated cylinder 

 least of all ; which also involves the reverse proposition, that a 

 reflecting surface, which in comparison with any other diminishes 

 the transmission of the heat by the above bodies, reflects the rays 

 of the Argand lamp in comparatively the least degree, that of 

 red-hot platinum better, that of the flame of alcohol with still 

 greater intensity, and that of the dark cylinder comparatively 

 best*. 



(Compare white and black velvet, p. 393 and 419; black 

 wood-charcoal and brown coal, p. 397 and 421 ; carmine and 

 black paper, p. 404 and 405, and p. 420 and 421.) 



2. That a substance by which heat is so reflected that it is 

 transmitted by some diathermanous media better or in the same 

 manner, by others less freely than that reflected by any other 

 surface, in comparison with the latter, sometimes reflects the 

 rays of the one, and sometimes of the other source of heat com- 

 paratively the best. 



(Compare red and green taffeta,pp. 392, 418 and 419; asphalt- 

 lac and black taffeta, p. 396 and 420 ; gypsum and peroxide of 

 copper, pp. 402, 403 and 420.) 



3. But that two surfaces which reflect the heat so that it per- 

 meates the diathermanous plates in the same manner, also con- 

 stantly reflect the rays of the different sources of heat with the 

 same relation to the intensities as has been found in either of them. 



(Compare white and black satin, p. 392 and 418; yellow 

 leather and brown Spanish leather, p. 395 and 419; silver and 

 sheet iron, p. 410 and 421.) 



Now M'hen we recollect that through red glass, blue glass, 

 alum, rock salt, calcareous spar and gypsum the heat of the Ar- 

 gand lamp passes best, that of red-hot platinum less freely, that 



* The raj's of the above four sources of heat, reflected by one and the same 

 surface, could not be directly compared, because it was impossible to give the 

 same direct intensity to the rays emitted by them in the position above described. 



