on the terrestrial Rays that occasion Heat. 297 



telescope/ which carried a Camera-eye-piece,* but no eye-glass. 

 When, by proper adjustment, the focus came to the ball of the 

 thermometer, it rose from 52 degrees to 1 10 ; so that rays which 

 came from the sun, underwent three regular reflections ; one, 

 on a concave mirror, and the other two, on two plain ones. 

 Now these rays, whether they were those of light or not, for 

 that our experiment cannot ascertain, had a power of occasioning 

 heat, which was manifested in raising the thermometer 58 

 degrees. 



zd. Experiment. Reflection of the Heat of a Candle. 



At the distance of 29 inches from a candle, I planted a small 

 steel-mirror, of 3^ inches diameter, and about 2^ inches focal 

 length. -f* In the secondary focus of it, I placed the ball of the 

 thermometer which in my paper has been marked No. 2 ; and 

 very near it, but out of the reach of reflection, the thermometer 

 No. 3. Having covered the mirror till both were come to the 

 temperature of their stations, I began as follows. 





No. 2. 



No. 3. 





In the focus. 



Standard* 



0' 



54 



54 



1 



55 



54 



s 



56 



54 



3 



57 



54 



4 



57$ 



54 



5 



57i 



54 



Here, in five minutes, the thermometer No. 2 received 3^ 

 degrees of heat from the candle, by reflected rays. I now 



• See Phil. Trans. Vol. LXXII. p. 176. 

 t See Plate XII. Fig. 1. 



