544 Sir DAVID BREWSTER on the Colours of Natural Bodies. 



Now, in both these experiments, the action of the colouring 

 matter of the decayed leaves is decidedly different from that of 

 the green juice, and there is no appearance whatever of the tints 

 having any such relation as that which subsists between adjacent 

 colours of the same order. 



From facts like these, which it is impossible to misinterpret, 

 . we are entitled to conclude, that the green colour of plants, 

 whether we examine it in its original verdure, or in its decaying 

 tints, has no relation to the colours of thin plates. 



I have submitted to the same mode of examination nearly 

 one hundred and fifty coloured media, consisting of fluids ex- 

 tracted from the petals, the leaves, the seeds, and the rhind of 

 plants, the different substances used in dyeing, coloured 

 glasses and minerals, coloured artificial salts, and different co- 

 loured gases ; and in all these cases I have obtained results which 

 lead to the same conclusion. I have analyzedj too, the blue 

 colour of the sky, to which the Newtonian theory has been 

 thought peculiarly applicable, but instead of finding it a blue 

 of the first order, in which the extreme red and the extreme 

 violet rays are deficient, while the rest of the spectrum was un- 

 touched, I found that it was defective in rays, adjacent to some 

 of the fixed lines of FRAUNHOFER, and that the absorptive ac- 

 tion of our atmosphere widened, as it were, these lines. Hence 

 it is obvious, that there are elements in our atmosphere which 

 exercise a specific action upon rays of definite refrangibility, and 

 that this, in some of these rays, is identical with that which is 

 exercised over them by the atmosphere of the sun. I have ob- 

 tained analogous results in analyzing the yellow, orange, red, and 

 purple light, which is reflected from the clouds at sunset ; but it 

 is impossible to convey any correct idea of the composition of 

 these colours, without a reference to the fixed lines of the spec- 

 trum, of which we at present possess no distinct nomenclature. 



I may mention, however, this general fact, that in the various 

 specific actions exercised upon light by solids, fluids, vapours, 



