KNOBLAUCH ON RADIANT HEAT. 



Table XII. 



221 



Thus, under those circumstances in which the same bodies ex- 

 hibit an unequal absorjitive power, their radiating jjoiver is one 

 and the same ; and those differences ivhich have hitherto been 

 observed when they are not heated to the same extent, are there- 

 fore pure functions of the former, and independent of the latter. 



In all cases therefore in which the elective absorption of cer- 

 tain substances is to be determined from the amount of heat 

 which they transmit to the thermoscope, it is a matter of in- 

 difference whether they are coated with lamp-black (see p. 206), 

 paper (p. 207), oi' ^ny other substance, for the purpose of in- 

 creasing their radiation upon the pile. Within the limits of the 

 experiments detailed, there will therefore be no fear of disturbing 

 the above differences by any foreign influence exerted by them. 



IV. Comparison of the Heat radiated from different bodies within 

 a certain range of Temperature. 



All former observations upon radiation have only related to 

 the quantities of heat emitted by different substances at certain 

 temperatures. The object of the present investigation is to 

 ascertain — 



Whether the heat which radiates from certain bodies, at one 

 and the same temperature or within certain limits of temperature, 

 is of a different kind, according as it is emitted by different bodies, 

 or is excited in them in a different way. 



