on the terrestrial Rays that occasion Heat. 451 



the end of this Paper, it stops 86 rays of light ; the number of 

 them coming from the object also being put equal to 1000. 



It should be remarked, that when I compare the interception 

 of solar heat with that of the light of a candle, it must not be 

 understood that I take terrestrial to be the same as solar light ; 

 but, not having at present an opportunity of providing a similar 

 table for the latter, I am obliged to use the former, on a suppo- 

 sition, that the quantity stopped by glasses may not be very 

 different. 



2,5th Experiment. 



I took a piece of flint glass, about 2^- tenths of an inch thick, 

 and fastened it oyer one of the holes of the transmitting appa- 

 ratus. 



*o 5 . 



No. 1. 



Sun. 



Flint glass. 



m 



m 



X4i 



7 1 



7*f 1 



7H 



74i 



7Si 



ttf . 1 



74. 



75i 



74! • 



• 5i' 5 = >9°9 

 Here the heat-making rays gave, in 5 minutes, £■§■ degrees to 



the thermometer No. 5 ; and, by transmission through the flint 



glass, 5 degrees to No. 1. Then, proceeding as before, we have 



4- = ,900. ; which shews that 91 rays of heat were stopped. 



In the table before referred to, we find that this glass stops 34, 

 rays of light. 



Before I proceed, it will be necessary to adopt a method of 

 reducing the detail of my experiments into a narrower com- 



