2^6 Experiments en tbc Solar and on the 



moved the lens, and, putting a plain glafs in the room of it, 

 I repeated the experiment with all the reft of the apparatus 

 in its former fituation. 



Here we find that both 

 thermometers receiv- 

 ed heat and parted 

 with it always in equal 

 quantities, which con- 

 firms the experi- 

 ment that has been given. And thus it is evident that 

 there are rays i filling from red-hot iron, which are fubjeet 

 to the laws of refraction, nearly equal to thofe which affect 

 light ; and that thefe rays are inverted with a power of caufmg 

 heat in bodies. 



l6tb Experiment. Refratlion of Fire-heat, by an InJIrument 

 refejnbling a Telejcope. 



It occurred to me that I might ufe A concave mirror to 

 condenfe the heat of the fire in the grate of my chimney, 

 and, reflecting it fideways by a plain mirror, I might after- 

 wards bring it to a fecondary focus by a double convex lens ; 

 and that, by this conftrucYion, I (hould have an inllrument 

 much like a Newtonian telefcope *. The thermometer would 

 figuratively become the obferver of heat, by being applied to 

 the place where, in the real telefcope of the fame conftrnc- 

 tion, the eye is fituated to receive light. Having put toge- 

 ther the different parts, in fuch a way as I fuppofed would 

 anfwer the end, I tried the effect by a candle, in order to 

 afcertaln the proper diftance of the obj eft- mirror from the 

 bars of the chimney-grate, .The front of the apparatus was 

 guarded by an iron plate, with a thick lining of wood •; and 

 the two thermometers which I ufed, were parted from the 

 mirrors and lens by a partition, which fcreened them from 

 the heat that was to be admitted through a proper opening 

 in the front plate, to come at the object-mirror. In the par- 

 tition was likewife an opening, of a fufficient diameter to 

 permit the rays to come from the eye-glafs to their focus, on 

 the ball of the thermometer No. r; while No. 4 was placed 



• Sec Plate VJII. fig. 2. 



h bv 



