Terrejlrial "Rays that occajion Heat. iy 



heads that have been propofed, I referve the three next, and. 

 a difcuffion which will be brought on by the feventh article, 

 for the fecond part. 



ijl Experiment. Reflection of the Heat of the Sun. 

 I expofed the thermometer, which in a former paper has 

 been denoted by No. 3, to the eye-end of a ten-feet New- 

 tonian telefcope, which carried a Camera eye-piece*, but no 

 eye-glafs. When, by proper adjustment, the focus came to 

 the ball of the thermometer, it rofe from 52 degrees to no; 

 fo that rays which came from the fun, underwent three re- 

 gular reflections; one on a concave mirror, and the other two 

 on two plain ones. Now thefe ravs, whether they were 

 thofe of light or not, for that our experiment cannot afcer- 

 tain, had a power of occafioning heat, which was manifefted 

 in railing the thermometer 58 degrees. 



2d Experiment. Reflection of the Heat of a Candle. 

 At the diftance of 29 inches from a candle, I planted a 

 fmall fteel mirror, of 3^ inches diameter, and about <x\ inches 

 focal length f- In the fecondary 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 ftations, I began 

 as follows : 



") Here, in five minutes, the 

 thermometer No. 2, re- 

 ceived 3^ degrees of heat 

 from the candle by re- 

 flected rays. I now covered 

 the mirror, but left all the 

 reft of the apparatus un- 

 touched. 



[ere, in fix minutes, the ther- 

 mometer loft the 3^ degrees 

 of heat again, which it had 

 gained before. I uncovered 

 the mirror once more. 



176. \ See Plate I. fig. 1. 



