1824.] Mr. Powell on Solar Light and Heat. 91 



be evident, agrees as nearly as we can expect with that before 

 obta lied for the heating effects developed upon or by the black 

 and white surfaces under examination ; and winch was shown to 

 be nearly the same, whether the light was in its ordinary inten- 

 sity or at a high degree of concentration. _ 



(41 ) We have thua established that with considerable differ- 

 ences in the intensity of light acting, the heating effects on a 

 Sand a Me surface maintain the same ^^"g^ 



It has also been shown that on the same surface, with different 

 JmSbrS hght, the heating effect is proportional to the 



1 Tttn / efnSiy it is shown that the heating effects on the 

 black and white surfaces are proportional to the quantities of 



tional to that impinging on the same surface. 



These conclusions contain, perhaps, no information absolute y 

 new but in establishing experimentally what seems hitherto to 

 have been only taken for granted on loose grounds, I conceive 

 we mav best prepare the way for investigating the nature of the 

 heatiS POwVr of light, and'for examining whether it be analo- 

 gous to any other phenomena. One step appears to me to be 

 lained in having, as I think, clearly shown the exact proportion- 

 Stv in the heat ng effect to the quantity of hgnt acting, and 

 shown to he actually absorbed by the surfaces These experi- 

 ments also confirm (if further proof be wanting) the conclusion 

 that the sun's heating effect is of a simple nature. 



(42) It may not be altogether superfluous here to remark, the 

 denendance^nhe results in the former portions of these inqui- 

 nesT ee 18) of the paper in the Annals for *™$>**™*^ 

 sLderations laid down in the present paper (28) It will be 

 thence evident that without knowing any thing of the relative 

 powera of the surfaces for absorbing simple heat or ntotaft* 

 En if any such heat were intercepted by the glass the eftect 

 on removing it would have been a diminution of .ratio by the 

 addition of equal quantities to its terms ; supposing that the 

 hea v ere inslantalously communicated from the : front to the 

 back of the bulb. If this were not the cas e bn ^ a certam time 

 were reauired for the effect to be produced, it would a .trie nrsi 

 TomeTbean addition of quantities in the vatu ><™**™rg™ 

 powers of the surfaces for simple heat: this in J e P"^^ 

 would be a ratio of « greater inequality, and as appears trom 



100 



(38) nearly m Vy 



Again, with respect to the subsequent experiment (Annals, 



