on the terrestrial Rays that occasion Heat. 453 



2,8th Experiment. 

 I examined a piece of Iceland crystal, of nearly two-tenths of 

 an inch in thickness. 



Sun, Iceland crystal. 



o' 67 67 



5 7 2 i 7ii---5f-4i=»75S 



It stops 244, rays of heat, and 150 of light. 



&gth Experiment. 



Sun. Talc. 



o' 67X 6 7 i 



5 7a 7i|---4t : 3it=>86i 



It stops 139 rays of heat, and 90 of light. 



30^ Experiment. 



Sun. An easily caklnable talc. 



o' 50 50 



5 54i 53lr---4i : 3|-=> 81 ^ 



It stops 184 rays of heat, and 288 of light. 



Transmission of solar Heat through Glasses of the prismatic 



Colours. 



Qist Experiment. 



Sun. Very dark red glass. 



°' 73 73 



5 79i 74i"- 6 i :1 £=> 20 ° 



This glass stops 800 rays of heat, and 999g, out of ten thou- 

 sand, rays of light ; which amounts nearly to a total separation 

 of light from heat. 

 mdccc. 3 N 



