204 Researches in regard to (he Manner 



in the thermometer A stood at 13° of Reaumur, and that 

 in B at 14°. The former, therefore, was the temperature of 

 the hght itself. 



Experiment II. 



I let the above apparatus remain without any change, but 

 suspended near the iherniometer B another, C, the bulb of 

 ■which was covered with a mixture of chalk and clear gum 

 water, and completely dried. 



Observation. — At the end often minutes the temperature 

 of the thermometers A and B was the same : in C the mer- 

 cury stood only at 12 degrees. 



Experiment III. 



T again left llic apparatus in the same state, but in place 

 of the thermometer C substituted a new one, D, the bulb 

 of which was covered with a mixture of gum water and ver- 

 milion completely dried. 



Observation. — At the end of ten minutes the mercury in 

 A and B was in the same state as before ; but in the ther- 

 mometer D, the bulb of which had been covered with ver- 

 milion, it stood at 17 degrees. 



Experiment IV. 



In the like manner I suspended near the thermometer B 

 another, E, the bulb of which was painted black, with a 

 mixture of lamp-black and gum water. 



Observation. — At the end of ten minutes the temperature 

 of the thermometers A and B was as before ; l)ut the one E, 

 painted with lamp-black, exhibited the temperature of 20°. 



The results of these experiments were striking, but I was 

 imcertain on what principle I could explain them. Two 

 explanations only were possible. 1st, Either the colours 

 which I employed act as conductors of heat : or, 2d, They 

 have different degrees of power to extricate heat from light. 

 To ascertain these points I made the following experiments: 



Experiment V. 



I took three cylindric glasses of equal thickness, and 

 filled one witli dry pounded chalk, ancjtherwith dry pounded 

 cinnabar, and the third with burnt lainp-black. In each 

 of these glasses I placed the bulb of a thermometer, in such 

 a manner that it was every where covered by the pulve- 

 rized substance. The three glasses were then deposited in 

 a small wooden box, and hot sand being poured over them, 

 ihey uere left at rest for ten minutes. 



Ohscrvatlon. — The temperature of the sand was now 50 



decrees 



