on the terrestrial Rays that occasion Heat, 30J 



thermometer No. 2, placed in the focus. Then, alternately 

 covering and uncovering the mirror, one minute at a time, the 

 effect was as follows. 









No. 2.- 



The mirror 



covered 



0' 



61 



Open 



- 



1 



68 



Covered 



- 



2 



61 



Open 



-- 



3 



64 



Covered 



- 



4- 



59 



Open 



-. 



5 



6if 



Covered- 



_, . 



6l 



& 



Here, in six minutes, we have a repeated result of alternate 

 elevations and depressions of the thermometer, all of which 

 confirm the reflexibility, the radiant nature, and the heating 

 power, of the invisible rays that came from the poker. 



From these experiments it is now sufficiently evident, that 

 in every supposed case of solar and terrestrial heat, we have 

 traced out rays that are subject to the regular laws of reflection, 

 and are invested with a power of heating bodies ; and this inde- 

 pendent of light. For though, in four cases out of six, we had 

 illuminating as well as heating rays, it is to be noticed that our 

 proof goes only to the power of occasioning heat, which has 

 been strictly ascertained by the thermometer. If it should be 

 said, that the power of illuminating objects, of these same rays, 

 is as strictly proved by the same experiments, I must remark, 

 that from the cases of invisible rays brought forward in the four 

 last experiments, it is evident that the conclusion, that rays 

 must have illuminating power, because they have a power of 

 occasioning heat, is erroneous ; and, as this must be admitted, 

 we have a right to ask for some proof of the assertion, that rays 



