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



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 stoppage of the other sort ; for, if it can 

 be shewn that heat and light are in this respect independent of 

 each other, it will follow that they must be occasioned by diffe- 

 rent rays ; and I shall make all possible objections to the ar- 

 guments I mean to draw from these tables, in order to shew 

 that no hypothesis will evade the force of our conclusions. 



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

 nearly three times as much heat as light ; whereas, crown glass 

 stops only about one-fourth 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, with- 

 " out 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 a hypothesis is made in order to explain any pheno- 

 menon of nature, we ought to examine how it will agree with 

 other facts ; and, in this case, we are already furnished with ex- 

 periments, which are decidedly against the supposition that has 

 been brought forward. For, the 14,8th and 149th experiments 

 shew 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 proved by the 94th experiment, that our bluish-white 

 glass stops a considerable portion of the heat that goes with the 



