Dr BREWSTER on a New Analysis of Solar Light. 129 



were, reappear, and by its predominance convert the extreme blue 

 space between n and N into Violet. 



In every part of a spectrum thus composed, there necessarily 

 exist three different colours, which form a compound tint by 

 their union ; and as the three differently coloured rays have, at 

 every point, the same refrangibility, it is impossible to separate 

 them, or to analyze the compound tint by prismatic refraction. 

 By transmitting the compound tint, however, through transparent 

 solids or fluids, which absorb one or more of the simple rays, and 

 allowing the rest to pass, we may exhibit one or more of the rays 

 separately, or obtain a residual colour, which indicates the pre- 

 sence of rays whose existence cannot be inferred from the origi- 

 nal colour of the compound tint. If, for example, we transmit 

 the compound ray at x, Fig. 4, through an absorbing medium, 

 which detains 27 red rays, we shaU obtain a transmitted tint 

 with 11 yellow rays and 10 of white light, or a brilliant yellow ; 

 and if we again transmit this light through another medium 

 which absorbs 1 1 yellow rays, we shall have a pure white light, 

 composed of 3 red, 5 yellow, and 2 blue rays. This white light 

 will exhibit the singular property of homogeneous light, namely 

 that of being indecomposable by the prism, and of being pre-emi- 

 nently adapted for the nicest purposes of vision. The existence of 

 such light has never even been conjectured, and its insidation at 

 any point of the spectrum becomes a proof of the existence, at 

 that point, of red, yellow, and blue rays of equal refrangibility. 



Having thus given a general view of the structure which I 

 have found in the spectrum, I shall now proceed to state the ex- 

 perimental evidence from which it has been deduced. 



From the simple inspection of the coloured spaces, it is ob- 

 vious that red light exists in the red, orange, and violet divisions 

 of the spectrum ; but, according to FRAUNHOFER'S measurements, 

 these three spaces occupy 190 parts when the whole length of 

 the spectrum is 360 ; hence red rays are observed in more than one 



