182 Dr BREWSTER on a Neiv Analysis of Solar Light. 



HOFER, which is far within the red space ; and, by the absorptive 

 action of these four last substances, the whole of the red space 

 has a yellowish tint, arising from the absorption of blue light. 

 The very same effect is produced, but in a more striking manner, 

 by transmitting the light of the red space through certain yellow, 

 orange, and green transparent wafers, all of which absorb some blue 

 light, and leave the whole of the red space of an orange tint, 

 that is, containing yellow light. In support of the opinion that 

 there are yellow rays in every part of the red space, I may adduce 

 a casual experiment of Sir W. HERSCHEL'S, when he had occasion 

 to view the prismatic spectrum reflected from clear turned brass. 

 " The colour of the brass," says he, " makes the red rays appear 

 like orange, and the orange colour is likewise different from what 

 it ought to be *." From these observations it follows, that yellow 

 light may be traced through all the coloured spaces except the 

 violet, where I have not yet been able to find it ; but this is not 

 surprising when we consider the great faintness of the violet rays, 

 and the facility with which they are absorbed by media of almost 

 all colours. Even the deep blue ammonio-sulphate absorbs al- 

 most the whole of the violet space, and the smalt blue glass nearly 

 one half of it, so that it is extremely difficult to subject it to the 

 partial action of absorbent media. 



It is obvious, even to the eye, that blue light exists in the 

 violet, indigo, blue, and green spaces, which occupy 247 parts 

 out of 360, or more than two-thirds of the whole spectrum. 

 When the most refrangible rays are absorbed by certain thick- 

 nesses of balsam of sulphur, balsam of Peru, pitch, or red mica, 

 the blue mixed with yellow, and forming green, may be traced 

 very near the line C of FRAUNHOFER, which is considerably within 



* Philosophical Transactions, 1800, vol. xc. p. 255. 



