g20 Dr. Herschel's Experiments on the solar, and 







No. 2. 



Screened 



8' 



$7\ A little red. 



Open 



10 



59% Doubtful. 



Screened 



12 



57-§- Not visible in my room darkened. 



Open 



14 



5H 



Screened 



16 



bl\ 



Open 



18 



5H 



Screened 



20 



57i 



Open 



22 



58 



Screened 



24 



57k 



Open 



26 



58 



Screened 



28 



57% . 



Now, the beginning of this experiment being exactly like 

 that of the 15th, with the thermometer No. 3 left out, the 

 arguments that have before proved the refraction of heat in one 

 state, will now hold good for the whole. For here we have a 

 regular alternate rising and falling of the thermometer, from a 

 bright red heat of the cylinder, down to its weakest state of 

 black heat ; where the effect of the rays, condensed by the lens, 

 exceeded but half a degree the loss of those that were stopped 

 by it. 



20th Experiment. Confirmation of the lgth. 



In order to have some additional proof, besides the uniform 

 and uninterrupted operation of the lens in the foregoing experi- 

 ment, I repeated the same, with an assistant thermometer, 

 No. 3, placed first of all at \ of an inch from No. 2, and more 

 towards the lens, but so as to be out of the converging pencil 

 of its rays, and also to allow room for the little screen between 

 the two thermometers, that No. 3 might not be covered by it. 



