SO Experiments on the Rays that occajzon Heat. 



°^ 54 .54^1 And, in five minutes, the 3^ degrees 



ll 56 54 I of heat were regained. In confe-. 



3 r $j 54 J qnence of which we are affured, 



5 57^ 54* tnat certain rays came from the 



candle, fubject to the laws of refle&ion, which, though they 

 might not be the rays of light, for that our experiment does 

 not determine, were evidently invefted with a power of heatn 

 jng the thermometer placed in the focus of the mirror. 



$d Experiment. RefleElion of the Heat that accompanies the 

 Solar prifmatic Colours. 



In the fpc&rum of the fun, given by a prifm, I placed my 

 fmall fteel mirror, with a thermometer in its focus*. It 

 was covered by a piece of pafteboard, which, through a 

 proper opening, admitted all the vifible colours to fall on its, 

 polifhed furface, but excluded every other ray of heat that, 

 might be either on the violet or on the red fide, beyond the 

 fpeclrum. Then, placing the apparatus fo as to have the 

 thermometer in the red rays, but keeping the mirror covered 

 up till the thermometer became fettled, I found it ftationary 

 at 58 . Uncovering the mirror, I had as follows : 



No. 2.^ Here, in two minutes, the thermometer rofe 

 o' 58 > 35 degrees, by reflected heat. I covered 



2 93 J ^ ie mi'" 1 " 01 ' again, and, in a few minutes, 



the thermometer expofed to the dire6l prifmatic red came 

 4own to 58 again. And thus the prifmatic colours, if they 

 «re not themfelves the heat-making rays, are at lea(| accom- 

 panied by fuch as have a power of occasioning heat, and are 

 liable to be regularly refiefted. 



J^th Experiment. Reflection of the Heat of a red-hot Pohr. 



I placed the fmall fteel mirror at twelve inches from a red- 

 hot poker, fet with its heated end upwards, in a perpendi- 

 cular pofition, and fo elevated as to throw its rays on the 

 mirror f. The thermometer No. 2, was placed in its fe- 

 condary focus, and had a fmall pasteboard fcreen, to guard; 

 its ball frqm the direct heat of the poker. 



* See Plate II. fig. 1. + See Plate I. fig. 1. 



No, 



