VOL. XC.] PHILOSOPHICAL TRANSACTIONS. 6Q5 



rays came from the candle, subject to the laws of reflection, which, though they 

 might not be the rays of light, for that our experiment does not determine, were 

 evidently invested with a power of heating the thermometer placed in the focus of 

 the mirror. 



Exper. 3. Reflection of the Heat that accompanies the Solar Prismatic Colours. — In 

 the spectrum of the sun, given by a prism, I placed my small steel mirror, with a 

 thermometer in its focus, fig. 2, pi. 12. It was covered by a piece of pasteboard, 

 which, through a proper opening, admitted all the visible colours to fall on its 

 polished surface, but excluded every other ray of heat that might be, either on the 

 violet or on the red side, beyond the spectrum. Then, placing the apparatus so as 

 to have the thermometer in the red rays, but keeping the 

 mirror covered up till the thermometer became settled, I ' 58 * 



found it stationary at 58°. Uncovering the mirror, I had 2 93 



as annexed. Here, in 2 minutes, the thermometer rose 35°, by reflected heat. I 

 covered the mirror again, and in a few minutes the thermometer, exposed to the 

 direct prismatic red, came down to 58° again. And thus the prismatic colours, if 

 they are not themselves the heat-making rays, are at least accompanied by such as 

 have a power of occasioning heat, and are liable to be regularly reflected. 



Exper. 4. Reflection of the Heat of a red-hot Poker. — I placed the small steel 

 mirror at 12 inches from a red-hot poker, set with its heated end upwards, in a 

 perpendicular position, and so elevated as to throw its rays Min N » 2 



on the mirror, fig. 1, pi. 12. The thermometer N° 2 was o^ 54£ 



placed in its secondary focus, and had a small pasteboard 



ij 93 



screen, to guard its ball from the direct heat of the poker. — I covered the mirror. 



Here, in 14- minute, the thermometer rose 38-±- degrees, by 



reflected rays; and when the mirror was covered up it fell in the next 14- minute, 

 28 degrees. On which account, we cannot but allow, that certain rays, whether 

 those that shine or not, issue from an ignited poker, which are subject to the re- 

 gular laws of reflection, and have a power of heating bodies. 



Exper. 5. Reflection of the Heat of a Coal Fire by a plain Mirror. — I placed a 

 small speculum, such as I use with my 7-feet reflectors, on a stand, and so as to 

 make an angle of 45 degrees with the front of it, fig. 3, pi. 12. This was after- 

 wards to face the fire in my parlour chimney, and would make the same angle with 

 the bars of the grate. At a distance of 3^ inches from the speculum, on the re- 

 flecting side of it, was placed the thermometer N° 1 ; and close by it, but out of 

 the reach of the reflected rays, the thermometer N° 4. The whole was guarded in 

 front, against the influence of the fire, by an oaken board 14- inch thick, which had 

 a circular opening of 1 4- inch diameter, opposite the situation of the plain mirror, to 

 permit the fire to shine on it. The thermometers were 

 divided from the mirror by a wooden partition, which 

 also had an opening in it, that the reflected rays might 

 come from the mirror to N° 1, while N° 4 remained 

 screened from their influence. On exposing this ap- 

 paratus to the fire, I had the annexed result. Here, in 



