KNOBLAUCH OX RADIANT HEAT. 



389 



heat of an Argand lamp, by a surface of white lead^ the centre 

 of which was 8 inches distant from the thermoscope, and the 

 normal of which was at an inclination of 4° to its longitudinal 

 axis, or at a distance of 9*75 inches and an inclination of 58°. 

 The same constant was found at every other distance and in- 

 clination, as also whatever was the size of the reflecting surface. 

 The experiments which were instituted on this point are con- 

 tained in the following table : — 



Table XXII. 



marked differences were discovered in them. Thus, when the 

 direct radiation of the Argand lamp (through a diaphragm) 

 upon the thermoscope had deflected the needle of the thermo- 

 multipHer 13°, on inserting the red glass it receded to 6°'59; 

 but when a similar deflection of 13° was produced by the heat 

 of the lamp diffusely reflected by vermilion, on inserting the 

 same glass it placed itself at 7°'04 ; and when the heat reflected 

 by carmine had produced this deflection, at 8°*33. Thus the 

 reflected heat, of the same direct intensity, passed through red 

 glass better than the unreflected, and that reflected by carmine 

 in a greater degree than that reflected by vermilion. The same 

 occurred with calcareous spar. Thus the unreflected rays of the 

 Argand lamp which passed through the plate of calcareous spar 

 to the pile, deflected the galvanometer-needle 15°- 19, those re- 

 flected by vermilion 17°'81 , and those reflected by carmine 22°*31, 

 when the deviation of the needle before the insertion of the cal- 

 careous spar amounted in each of the three cases to 25". 



The following table exhibits the differences which occurred with 

 other reflecting pigments and other diathcrmanous bodies : — 



