KNOBLAUCH ON RADIANT HEAT. 



233 



less for the rays of the cylinder than for those of the Argand 

 lamp. 



With letter 2]aper the difference in the indications produced 

 by the removal of the lamp-black becomes reversed. Thus, 

 whilst by heating the paper coated next the pile with lamp- 

 black with the rays of the flame, a deflection of 1 8°'37 was found, 

 and with those of the dark cylinder 21'^*13 ; in the uncoated one, 

 in the first case it amounted to 22°'25, in the last to 20°"5. On 

 this occasion transmission also occurs, which acts in opposi- 

 tion to the heating, and preponderates to such a degree, that it 

 not only overcomes the influence of the unequal absorption, but 

 even produces a change of the difference to the other side. 



This also occurred with ivory, as may be seen from the fol- 

 lowing table, which contains the details of the observations 

 (arithmetic means of every two) : — 



Table XX. 



These changes of the difference of the thermoscopic indica- 

 tions on removing the coating of lamp-black would not occur in 

 adiathermanous bodies. 



Hence it is proved that black glass, black asphalt-lac, a thin 



