75 °* RADIANT HEAT. 



the focus of one, a lighted candle into the focus of the other 

 reflector. In two minutes the thermometer fluid rose 63*. 

 This [ determined by taking the mean of six experiments, 

 the results of which, from attention to the burning of the 

 candle, were very nearly alike. 



I procured three skreens; one of painted glass, one of 

 painted tin (both black), the other of plain glass. They 

 served for the following experiments. 



Exp. 2. Exp. 2. I placed a skreen stand midway between the 



two reflectors. On this I fixed the painted glass skreen ; 

 in two minutes the thermometer rose 2°: repeated, 2°: re- 

 peated, ]|°. 



■Exp. 3. Exp. 3. I exchanged the painted glass for the paiuted 



tin. Jn two minutes the thermometer rose 1|°: repeated, 

 11°: repeated, if. 



Exp. 4. Exp, 4. Having removed the painted tin, and interposed 



the plain glass, the thermometer rose in two minutes 25°: 

 repeated, 26°: repeated, 254°. 



Exp. 5. Exp. 5, The apparatus remaining as in the preceding 



experiments, and the glass skreen resting on the stand, 

 when the thermometer had fallen to zero, I brought the 

 lighted candle into the focus of the first reflector; the ther- 

 mometry fluid mounted in two minutes to 24°. I removed 

 the candle, but left the skreen. The thermometer did not 

 rise in the slightest degree, and in 30" it had fallen 3°; in 

 45", 8°; in 6o", 12°; in 75", 14°; in 90", i6°; in 105", 18°; 

 and in 2', |ft*J 



Exp. 6. Exp, 6. I substituted the painted for the plain glass. 



In two minutes the thermometer was at 1^°. I removed the 

 candle, the skreen remaining on the stand ; in one minute 

 the thermometer rose 1 -V* more, and after a short time it be- 

 gan to fall. 



Exp. 7. Exp, 7. Having fixed the blackened glass skreen on the 



stand, I brought into the focus of the first reflector a 7oz. 

 flask, containing A~ oz. of a boiling mixture of sulphuric 

 acid and water, the boiling point of which was somewhere 

 between 450° au'J 500° Fah. In two minutes the thermo- 

 meter rose \\ n . *i removed the flask — the thermometer con- 

 tinued to rise until at l|° of the scale. 



Fxp. 8. Exp. 8. I interposed the plain instead of the painted 



glass 



