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



of it ; but since, by calcination, the talc lost much of its trans- 

 mitting power, we may easily account for this unexpected 

 regularity. 



123d Experiment. 



Fire. Very dark red glass. 



66 66 



%9t 75 • • • 23i : 9 = >3 8 7 



This glass stops 613 rays of fire-heat. 



124^/6 Experiment. 



Fire. Dark-red glass. 



o' 67 67 



5 92! 78...25I: n = ,427 



This glass, which stops 999,8 rays of candle-light, stops only 

 573 ravs °f fire-heat; whereas my piece of thick flint glass, 

 which stops no more than 9 1 rays of that light, stops no less 

 than 750 of fire-heat. It does not appear, by looking through 

 these glasses, that there is a difference in their disposition to 

 transmit candle-light or fire-light. 



12 $th Experiment. 



Fire. Orange glass. 



o' 66 66 



5 80 71 ...14 -.5 = ,357 



It stops 643 rays of fire-heat. 



126^ Experiment. 



Fire. Yellow glass. 



o' 6l± 6ii 



5 83 68£...2i:7f.cor.-if.2of:6x = ,3i 5 



