KNOBLAUCH ON RADIANT HEAT. 



Table XI. 



219 



To make this experiment in a more direct manner, I heated 

 the radiating bodies also immediately by the diiferent rays. 



For this pm'pose I substituted a plate of charcoal for the paper 

 coated on both sides with lamp-black, and obtained the same 

 result as before. I placed carmine upon some wire-gauze, which 

 had the effect of keejjing its separate parts together. When 

 it was exposed in this manner before the thermal pile to the rays 

 of an Argand lamp or the metallic cylinder at 212° F., which 

 produced the same direct deflection, in both cases different in- 

 dications were given by the instrument. 



The question was, Mhether this difference was only to be 

 ascribed to the unequal absorption of the different rays by the 

 carmine-surface, or whether its radiating power was also con- 

 cerned in it. 



I tried to convince myself of this by the following experi- 

 ment; — If the carmine-surface next the pile is coated wiih 

 lamp-black, whilst upon the other side the sources of heat men- 

 tioned act upon it, the difference observed in the galvanometer 

 arises solely from the carmine-surface absorbing the heat of the 

 heated metallic cylinder to a greater extent than that of the 

 Argand lamp ; for, as we are aware, the radiation from the 

 carbon-surface does not in this case produce any difference. 

 But if the coating of lamp-black be removed, so that the carmine 



