§26 Dr. Herschei/s Experiments on the solar, and 



t* we may surmise that the 914 rays of light, together with the 

 " 300 of the invisible rays which are transmitted, make up the 375 

 " rays of heat which pass through the glass. Hence, by algebra, 

 " we have the number of invisible heat-rays 878, and the number 

 " of the visible ones 122. Then, to try how this will answer, if 

 " 1000 rays of light give 122 of heat, 86 will give 10 ; and, if 

 rc out of a thousand invisible rays 700 be stopped, 878 will give 

 " 615 to be intercepted. The sum of these will be 625, which is 

 " exactly the number pointed out by our table." Now this being 

 a fair solution of one instance, let us see how it will agree with 

 some others. 



Before I proceed, however, I cannot help remarking, that 

 the supporters of visible heat-rays must feel themselves already 

 considerably confined, as our present argument will not allow 

 them more than 122 of such rays out of a thousand. 



Now, if the assumption that terrestrial heat is owing to a 

 mixture of visible and invisible rays, in the proportion of 122 

 of the former to 878 of the latter, be well founded, it ought to 

 explain every other phasnomenon collected in our table. 



The purple-coloured glass stops 993 rays of light, which, 

 according to our present hypothesis, should stop 121 rays of 

 heat : it also stops 730 invisible rays, which will give 641 rays 

 of intercepted heat ; therefore this glass should stop 762 rays of 

 heat, out of every thousand that come from a candle ; but, from 

 our table, we find that it stops no more than 520, so that 242 

 rays cannot be accounted for. 



The glass with an olive colour burnt into it, stops 984 rays 

 of light, or 120 of heat, and 637 invisible rays, or 5$g of heat. 

 The sum is 6yg which that glass should stop ; but it stops ac- 

 tually 792 ; so that, as in the foregoing instance we had* a defi- 



