Terrejtrial Rajs that occajlon Ileal. 131 



No. 3, from change of temperature, rofe only one, notwith- 

 ilanding its expofure to the ftove was in every refpe£t equal 

 to that of No. 3, except fo far as relates to the rays returned 

 by the mirror; and therefore the radiant nature of thefe in- 

 vifible rays, their power of heating bodies, and their being 

 fubject to the laws of reflection, are equally ellablifLed by 

 this experiment. 



lotb Experiment. JiefleEtion of the invifible Rays of Heat vf 



a Poker, cooled from being red-hot till it could no longer 

 be feen in a dark Place. 



The great abundance of heat in my laft experiment would 

 <not allow of its being carried on without injury to the ther- 

 mometer, the fcale of which is not extenfive ; I therefore 

 placed a poker, when of a proper black heal, at 12 inches 

 from the fteel mirror *, and received the effect of its con- 

 denfed rays upon the thermometer No. 2, placed in the focus. 

 Then, alternately covering and uncovering the mirror, ope 

 minute at a time, the effect was as follows : 



No. 2."} Here, in fix minutes, 

 we have a repeated 

 refill tof alternate : ele- 

 vations and depref- 

 fions of the thermo- 

 meter, all of which 

 confirm the rerlexi- 

 bility, the radiant 

 Mature, and the heating power of the invifible rays that came 

 from the poker. 



From thefe experiments it is now fufficiently evident, that in 

 every fuppofed cafe of folar and terrcftrial heat, we have traced 

 out ravs that are fubiect to the regular laws of reflection, and 

 <nc inverted with a power of heating bodies ; and this inde- 

 pendently of light. For, though, in four cafes out of fix, we 

 bad illuminating as well as heating rays, it is to be noticed 

 that our proof noes only to the power of occafioning heat, 

 which has been ftrictlv afcertained by the thermometer. If 

 it fliould be faid, that the power of illuminating objects of 

 fame ravs i~ as firietly proved by the fume experiments, 

 1 Bee Plate l.Ui:,. 1. 



s 2 1 mult 



