l6o Experiments on the Solar and on the 



No. 2. 



Very red-hot 

 Red-hot. 

 Still red-hot. 

 Still red. 

 A little red. 

 Doubtful. 

 57 \ s Not vifible in my )• 

 room darkened 



"] Now, the begin- 

 ning of this ex- 

 periment being 

 exactly like that 

 of the 15th, with 

 the thermome- 

 ter No. 3 left 

 out, the argu- 

 ments that have 

 before proved the. 

 refraction of heat 

 in one ftate, will 

 now hold good 

 for the whole. 

 For here we have 

 a regular alter- 

 nate ruing and falling of the thermometer, from a bright red 

 heat of the cylinder, down to its weakeft Mate of black heat ; 

 where the effect of the rays, condenfed bv the lens, exceeded 

 but half a degree the lofs of thofe that were Hopped by it. 



CZOlb Kxptrunent. Confirmation of the igth. 



In order to have fomc additional proof, befides the uniform 

 and uninterrupted operation of the lens in the foregoing ex- 

 periment, I repeated the fame with an affittant thermometer, 

 No. 3, placed firft of all at i of an inch from No. 2, and 

 more towards the lens, but fo as to be out of the converging 

 pencil of its rays, and alfo to allow room for the little fcreen 

 between the two thermometers, that No. 3 might not be 

 covered bv it. 



No. 3. "j Here No. 3, be- 



Advanceil Tideways. 

 Always open. 



63 



64 

 64 



64! 



64I- 



64 



64 



ing out ot the 

 reach of re- 

 fraction, gra- 

 dually acquir- 

 ed its maxi- 

 mum of heat, 

 in confe- 

 quence of an 

 uniform ex- 

 pofure to the 

 influence of 



the hot cylinder ; after which -it began to decline. 



No. 2, on 

 the 



