492 Dr. Herschel's Experiments on the solar, and 



precaution I had taken, of having two sets of it, that one might 

 be cooling while the other was employed, and though neither 

 of them was ever very hot, yet I found that so much heat came 

 to the box, that when it was taken out of the bricks, in order to 

 be cooled, the thermometers continued still to rise, at an ave- 

 rage, about two degrees higher than they were. I have therefore 

 now taken the third minute, as a much safer way to come at 

 the truth. 



170^ Experiment. 



Stove. Bluish-white glass. 



3 59i 56% ■- • • 3f '• H = ,3oo 



This glass stops 700 invisible rays of heat. 



171^ Experiment. 



Stove. Flint glass. 





0' SSi £3i 





3 55i 54f • • 



• 1 s : i = ,4 6 7 



It stops 533 invisible rays of heat. 





172^ Experiment. 





Stove. Crown glass. 





o' 5°t 5o i 





3 53% 5H- 



•2£:-i- = ,2i7 



It stops 783 invisible rays of heat. 



173d Experiment. 



Stove. Coach glass. 



It stops 625 invisible rays of heat. 



