132 Experiments on the Solar and on the 



I mud remark that, from the cafes of invifible rays brought 

 forward in the four laft experiments, it is evident that the 

 conclufion that ravs mutt have illuminating power becaufe 

 thev have a power of occafioning heat is erroneous; and, as 

 this mud be admitted, we have a right to afk for forne proof 

 of the aflejtiori, that rays which occafion heat can ever be- 

 come vifible. But, as we fliail have an opportunity to fay 

 more of this hereafter, I proceed now to inveftigate the re- 

 fraction of heat-making rays. 



\l th Experiment. RefraSiion of Solar Heat. 

 With a new len-feet Newtonian telefcope, the mirror of 

 which is 24 inches in diameter of polifhed furfacc, I received 

 the ravs of the fun; and, making them pafs through a day- 

 piece with four lenses, I caufed them to fall on the ball of 

 the thermometer No. 3, placed in their focus. Thofe who 

 are acquainted with the lines in which the principal rays and 

 pencils move through a fet of glafi'es, will eafilv conceive how 

 artful]v, in our prcfent inftancc, heat was fent from one 

 place to another — heat trotting heat, through many intcr- 

 fecVmg comie , without joftljng together, and each parcel 

 arriving at la it fafely to its deflined place. As foon as the 

 ravs were brought to the thermometer, it rofe, ahnoft inttant- 

 lv, from 60 degrees to 130 ; and, being afraid of cracking the 

 glades, [ turned away the telefcope. Here the rays, which 

 occafioned no lei's than 70 degrees of heat, had undergone 

 pight regular fucceffive refractions ; fo that their being lubjeft 

 fo its laws cannot be doubted. 



l%t& Experiment. Refraellon of the Heat of a Candle. 



I placpd a lens of about 1,4 inch focus and 1,1 inch dia- 

 meter, mounted upon a fmail fupport, at a diftance of 2,8 

 inches from a candle*; and the thermometer No. 2, be- 

 hind the lens, at an equal diftance of about 2,8 inches ; but 

 which ought to be very carefully adjutted to the fecondary 

 focus of the candle. Not far from the lens, towards the 

 caml'e, was a pafleboard fcreen, with an aperture of nearly 

 ihe fame fize as the lens. The fupport of the lens had ai> 



* Sec Plate IV. i\£- 3- 



eccentric 



