KNOBLAUCH OX RADIANT HEAT. 



407 



red-hot platinum exhibited after reflexion by the same bodies. 

 The same was the case in the differences noticed with other 

 diathermanous bodies, as also in those which were obsen^ed in 

 the rays reflected by the other surfaces on transmission through 

 red glass, blue glass, alum, rock salt, calcareous spar and gypsum. 

 An examination of the heat of an iron cylinder heated to about 

 212° F., reflected by the same bodies, yielded the results con- 

 tained in the following table : — 



Table XXXVII. 



the insertion when the heat of the hot metallic cylinder is reflected by 



Hence these experiments prove that the modifications which 

 heat experiences on reflexion are very considerable in the case 

 of the heat emanating from an Argand lamp ; that with the 

 heat of the red-hot platinum they diminish; with the heat of 

 the flame of alcohol they are still less ; and in the case of the 

 heat emitted by a heated iron cylinder, of whatever tempera- 

 ture it may be, between 79° and about 234° F.*, they absolutely 

 vanish. 



To render this still more distinct, I repeated the experiments 

 detailed also at greater deflections than those already given. 

 The numbers which were found are arranged in the folio wins 

 table : - 



Table XXXVIII. 



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



• The limit, 320° F., given in tlie Monthly Report of the Berlin Academy 

 for May 1815 is too higli. When the temperature of tlie cylinder is ahove 234° 

 F. (thus at a temperature which is far too low to produce a visii)le red heat), 

 difierences do occur in the transmission of the heat reflected hy different hodies. 



