VOL XC.] PHILOSOPHICAL TRANSACTIONS. 773 



a dark blue glass stops only 362 rays of heat, but intercepts 801 of light ; and a 

 dark red glass stops no more than 606 rays of heat, and yet intercepts nearly all 

 the light ; scarcely one ray out of 5000 being able to make its way through it. 



Before proceeding to a more critical examination of these results, it will be 

 necessary to add also a table of the same kind, collected from the experiments with 

 liquids. 



Table 3. 

 Rays of heat. Of light. Rays of heat. Of light. 



Empty tube and 2 glasses stop 542 and 204 Spirit of wine 612 and 224 



Spring water 558 211 Gin 739 £26 



Sea water 682 288 Brandy 791. ggQ 



To which may be joined, a table containing the stoppages occasioned by scatter- 

 ing substances. 



Table 4. 

 Rays of heat. Of light. Rays of heat. Of light. 



Rough crown glass stops 464 and 854 Olive colour, burnt in 839 and 984 



Rough coach glass -571 879 Calcined talc 867 996 



The 1st doubly rough 667 932 White paper 850 994 



The 2d doubly rough 735 946 White linen 916 952 



The 2 first together 698 9^9 White persian 760 916 



The 2 next together 800 979 Black muslin 714 737 



The 4 first together 854 995 



We shall now enter more particularly into the subject of these 4 tables, that we 

 may, if possible, find a criterion by which to judge whether heat and light can be 

 occasioned by the same rays or not. Now this I think will be obtained, if we can 

 make it appear that stopping one sort of rays does not necessarily bring on a stop- 

 page of the other sort ; for if it can be shown that heat and light are in this 

 respect independent of each other, it will follow that they must be occasioned by 

 different rays ; and I shall make all possible objections to the arguments I mean to 

 draw from these tables, in order to show that no hypothesis will evade the force of 

 our conclusions. It has been noticed, that bluish-white and flint glasses stop 

 nearly 3 times as much heat as light ; whereas crown glass stops only about ± more 

 of the former than of the latter. Now in answer to this it may be alleged, " that 

 the ingredients of which the former glasses are made, dispose them probably to 

 stop the invisible rays of heat, and that consequently a great interception of it may 

 take place, without bringing on a necessity of stopping much light ; and that, on 

 the other hand, the different texture of crown glass may stop one sort of heat as 

 well as the other, so that nearly an equality in this respect may be produced." 



When an hypothesis is made in order to explain any phenomenon of nature, we 

 ought to examine how it will agree with other facts ; and in this case we are already 

 furnished with experiments, which are decidedly against the supposition that has 

 been brought forward. For the 148th and 149th experiments show that the bluish- 

 white and flint glasses transmit all, or nearly all, the invisible rays of solar heat ; 

 whereas crown glass, by the 150th experiment, stops a considerable number of 

 them. But, to assist the objecting argument, let it be alleged, as has been 



