254 Experiments on the Solar and on'thi 



No. i. No. 4. "J Here, in nine minutes, the ray$ 



Burning lens. Screened. coming from the fi'C, through 



o' 58 58 the burning glafs, gave 9I 



I'J 65 60 : decrees of heat more to the 

 Ay <t r .u!:.. !_.. xt.'. _ .u-.^ 



3 68 61 



5 70 6r 



7 7*t 6l l 



thermometer No. 1, than 

 No. 4, from change of tem- 

 perature, had received behind 

 9 71^- 61 1- J the fcreen. Now, to deter- 



mine whether this was owing merely to a tranfmifiion of 

 heat through the glafs, or to a condensation of the rays, by 

 the refraction of the burning lens, I took away the lens, as 

 foon as the laft obfervation of the thermometers was written 

 down, and continued to take down their progrefs as follows : 



Here the diieft rays of the 

 fire, we fee, could not keep 

 up the thermometer No. 1 ; 

 which loft %~ degrees of 

 heat, notwithstanding the 

 lens intercepted no longer 



Here again, the lens afted as a 

 condenfer of heat, and gave 1^ 

 degrees of it to the thermometer 

 No. 1. I now once more took 

 away the lens, and continued 



25']- 71 61^ This again confirms the fame bv 



31 68 6r : ij a loTs of 3 degrees of heat; 1 



reftored the lens once mxSre, and had a^ follows : 



No. r. No. 4.^ And here the thermometer 



Binning Lens. Serened. I received 1 '- degree of heat 

 $i'\: 68 61} J again ; fo that, in the courfc 



35 69^ 61?- J of 35 minutes, the thermo- 



meter No. 1 was alternately raifed and deprefied five times, 

 bv rays which came from the chimney fire, and were fubjecl: 

 to laws of refraction, not fenfibly different from thofe which 

 affect light. 



l£tb Experiment. RefraSion of the Heat of red-hot Iron. 



I caufed a lump of iron to be forged into a cylinder of %\ 

 9 inches 



