on the terrestrial Rays that occasion Heat. 493 



174^ Experiment. 



Stove. Iceland crystal. 



o' 47 4 6 i 



3 54l 48|-...7i : 2!=> 2 74 



This substance stops 726 invisible rays of heat. 



iy^tb Experiment. 



Stove. Calcinable talc, 



o' 5.1 51 f 



3 57? 54i...6i:sf = ,404 



At the end of five minutes, when the box was taken out of 

 the bricks, the talc was perfectly turned into a scattering sub- 

 stance : as such, it stops 596 scattered invisible rays of heat. 

 The sun cannot be seen through it ; but this I find is chiefly 

 owing to its scattering disposition. It stops however 997 scat- 

 tered rays of light. 



176^ Experiment. 



Stove. Dark red glass. 



o' 58 5 8 



3 6 4j 6oi'...6J:ai=a,37o 



This glass stops 630 invisible rays of heat. 



177^ Experiment. 



Stove. Orange glast. 



°' 55i 55i 



3 6o± 57|".5£:2i=,4,76 



It stops 524 invisible rays of heat. 



mdccc. 3 S 



