knoblauch ox radiant heat, 

 Table ZXIII. 



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



391 



those series marked with an =:, from their similarity.) 



of the differences obsei'ved from the addition of the heat of the 

 reflecting surfaces themselves to the rays from the original source 

 of heat ; for, as we know (see Table XV. pp. 225 and 226), the 

 former are less perfectly transmitted by all the diathermanous 

 media used than those of the Argand lamp. Thus, to give a 

 single instance, the rays of heat emitted by a body below 234° F., 

 which have produced a direct deflection of 25°, after the inser- 

 tion of the calcareous spar, cause the needle to deviate 5°'69 ; 

 those from an Argand lamp, exerting the same direct action, 

 after the insertion of the same plate, deflect the needle 15°" 19. 

 Hence, if the former were added to the latter, so as when united 

 with them to produce a deflection of 25°, a less deviation than 

 15°'19 should occur after the insertion of the calcareous spar. 

 An increase to 22°*31, however, as we found e.g. with the car- 

 mine (Table XXIIL), would be utterly impossible. 



It appeared to me interesting, with regard to the present 

 question, to compare the same substances, but of different colours, 

 with each other. 



On so doing, it appeared that, e. g. the heat reflected by white 

 and black satin, as also that by white and black taffeta, could 

 not be distinguished by radiation through the above bodies ; for 

 the rays of heat emitted by all these surfaces, which passed 

 through the red glass, deflected the needle of the multiplier 

 7°'54-7°*5H, when their direct action produced an indication of 

 13°, and those passing through the calcareous spar caused a de- 

 viation of 1 7°-12-l7°'50 in the needle when the deflection before 



