T-erreJlrla! Rays that oxcqfion Heat, 127 



rays might come from the mirror to No. 1, while No. 4 

 remained fcreened from their influence. On expofing this- 

 apparatus to the fire, I had the following refult : 



No. 1. No. 4."} Here, in five minutes, the heat re- 

 flected from the plain mirror raifed 

 the thermometer No. 1, 7 de- 

 grees; while the change in the 

 temperature of the fcreened place, 

 indicated by No. 4, amounted 

 only to half a degree: which (hows 

 that an open fire fends out rays that are fubjeel: to the laws of 

 reflection, and occafiun heat. 



€tb Experiment. RsfltElion of Fire-Heat by a Prifm. 



Every thing remaining arranged as in the 5th experiment, 

 I removed the fmall plain mirror, and placed in its (lead a 

 p-rihn which had one of its angles of 90 degrees, and the- 

 ether two of 45 degrees each *. It was put fo as to have 

 one of the fides facing the fire, while the other was turned 

 towards the thermometer: the hypotenufe, confequently, 

 made an angle of 45 degrees with the bars of the grate. The 

 apparatus, after having been cooled fome time, was expofed 

 to the fire, and the following refult was taken: 



No.'r 1 ." No. 4."! Here, in eleven minutes, th_ 

 J*i 62 l r rays refleded by the prifm 



2 



63 62 



64 6 3 



raifed the thermometer ±\. 

 degrees ; but, the temperature 



4 64^- 63 y of the place having undergone 



an alteration of 1 \ degrees, we 

 can only place %\ to the ac- 

 count of reflection. The ap- 



| 6 5 ■ 63" 



H 6 5l 63!- 



10 66!- 62 L 



1 1 



67 64^ J paratus becoming now very- 



hot, it wouid not have been fair to have continued the ex- 

 periment for a longer time; but the effect already produced 

 was fully Efficient to (how, that even a prifm, which flops 

 a great many heat-making rays, (till refle&s enough of them 

 to prove, that an open fire not only fends them out, but that, 

 they are fubject to every law of reflection. 



• Sec Plate II. % 2. F. 



