"^30 'Experiments on the Sslar and on the 



No. 2. -v Here, in two minutes, the 



iii the Focus of Tnvifible Heat. T thermometer rofe 24 de- 



§ 83 T grees. I covered the min- 



6 88 J ror once more, 



7' 69 — And, in one minute, the thermometer fell 



19 degrees. Now, by this alternate rifing and falling of the 

 thermometer, three points are clearlv ascertained. The firft 

 is, that there are invifible rays of the fun. The fecond, that 

 thefe ravs are not only reflexible, in the manner which has 

 been proved in the foregoing experiment, but that, by the 

 ftriet laws of reflection, they are capable of being condenfed. 

 And, in the third place, that by condenfation their heating 

 power is proportionally increafed ; for, under the circum- 

 ftances of the experiment, we find that it extended fo far as- 

 to be able to raife the thermometer, in two minutes, no lefs 

 than 24 degrees. 



gth Experiment. Rcflc&ion of "invijibh Culinary Heat. 



1 planted mv little fteel mirror upon a finall board *, and 7 

 sit a proper diftance oppofite to it, I creeled a flip of deal, 

 4- inch thick and 1 inch broad, in a horizontal direction, fo as 

 to be of an equal height, in the middle of it* thicknefs, with 

 the centre of the mirror. Againft the fide, facing the mirror, 

 were fixed the two thermometers No. 2 and No. 3, with their 

 balls within half an inch of each other, and the fcales turned 

 the oppofite way. A little of the wood was cut out of the 

 flip, to make room for the balls to be freely expofed. That 

 of No. 2 was in the axis of the mirror, and the ball of No. 3 

 w as fcreened from the reflected rays by a fmall piece of pafte- 

 feoard tied to the fcale. The fmall ivory fcales of the ther- 

 mometers, with *he flip 01 wood at their back, which, how ever, 

 \vas feather-edged towards the (tove, intercepted fome heatj 

 but it will be feen prefentlv that there was enough to fpare. 

 When my iiove was of a good heat, I brought the apparatus 

 to a place ready prepared for it. 



No. 2. No ■]. ~\ Here wc find that, in one mi- 



Li the Focus. Screen*!. I nute, the invifible culinary 



<$' 53 52 I heat raifed the thermometer 



T 91 M J No. 2, 39 degrees ; while 



* ieU'lats IV. %■:-., 



No. 3, 



