KNOBLAUCH ON RADIANT HEAT. 



401 



the needle. The same is the case with the other diathermanous 

 substances. 



In the case of metallic surfaces, the diffuse reflexion from which 

 does not exert the least influence upon the transmission of the 

 heat by radiation through those diathermanous plates which have 

 been hitherto experimented upon (see Table XXIX.), it is, in 

 fact, a matter of indifference whether they are used in a reflecting 

 or any other condition of the surface. In this case also the sub- 

 joined table contains the values observed : — 



Table XXXI. 



the insertion when the heat of the Argand lamp is reflected by 



reflected rays. But the heat reflected e. g. by green velvet 

 (see p. 393) radiates through alum, calcareous spar and gyp- 

 sum better than, red glass as well as, and rock-salt less perfectly 

 than the direct rays of the flame. The same occurs with other 

 surfaces. 



In the following table I have grouped some examples which 

 are characteristic in this point of view, in Mhich those columns 

 especially which are marked with the same letter when compared 

 exhibit peculiar relations : — 



Table XXXII. 



when the heat of the Argand lamp is reflected by 



Those imnibers separated hy the dark lines are not comparable witli each other 

 VOL. V. PART XIX. 2 K 



