tier, in.], DISSERTATION SECOND. 71 



Blue - - 60 



Indigo - - 40 



Violet - - 80 



Between the divisions of the spectrum, thus made by the dif- 

 ferent colours, and the divisions of the monochord by the 

 notes of music, Newton conceived that there was an analogy, 

 and indeed an identity of ratios; but experience has since 

 shown that this analog)' was accidental, as the spaces occupi- 

 ed by the different colours do not divide the spectrum- in the 

 same ratio, when prisms of different kinds of glass are em- 

 ployed. 



Such were the experiments by which Newton first " un- 

 twisted all the shining robe of day," and made known the tex- 

 ture of the magic garment which nature has so kindly spread 

 over the surface of the visible world. From them it followed, 

 that colours are not qualities which light derives from refrac- 

 tion or reflection, but are original and connate properties con- 

 nected with the different decrees of refrangibility that belong 

 to the different rays. The same colour is always joined 

 to the same degree of refrangibility, and conversely, the 

 same degree of refrangibility to the same colour. 



Though the seven already enumerated are primary and 

 simple colours, any of them may also be produced by a mix- 

 ture of others. A mixture of yellow and blue, for instance, 

 makes green ; of red and yellow, orange ; and, in general, if 

 two colours, which are not very far asunder in the natural 

 series, be mixed together, they compound the colour that 

 is in the middle between them. 



But the most surprising composition of all, Newton ob- 

 serves, is that of whiteness ; which is not produced by on;; 

 sort of rays, but by the mixture of all the colours in a 

 certain proportion, namely, in that proportion which they 

 have in the solar spectrum. This fact may be said t« 



