466 POPULAR SCIENCE MONTHLY. 



1. As the rays of light differ in degrees of refrangibility, so they 

 also differ in their disposition to exhibit this or that particular colour. 

 Colours are not qualifications of light, derived from refractions, or 

 reflections of natural bodies (as it is generally believed,) but original 

 and connate properties, which in divers rays are diverse. Some rays 

 are disposed to exhibit a red colour, and no other; some a yellow, and 

 no other; some a green, and no other, and so of the rest. Nor are 

 there only rays proper and particular to the more eminent colours, 

 but even to all their intermediate gradations. 



2. To the same degree of refrangibility ever belongs the same 

 colour, and to the same colour ever belongs the same degree of re- 

 frangibility. The least refrangible rays are all disposed to exhibit 

 a red colour, and contrarily, those rays which are disposed to exhibit 

 a red colour, are all the least refrangible: so the most refrangible 

 rays are all disposed to exhibit a deep violet-colour, and contrarily, 

 those which are apt to exhibit such a violet colour, are all the most 

 refrangible. And so to all the intermediate colours, in a continued 

 series, belong intermediate degrees of refrangibility. And this analogy 

 betwixt colours, and refrangibility, is very precise and strict; the rays 

 always either exactly agreeing in both, or proportionally disagreeing 

 in both. 



3. The species of colour, and degree of refrangibility proper to 

 any particular sort of rays, is not mutable by refraction, nor by 

 reflection from natural bodies, nor by any other cause, that I could 

 yet observe. When any one sort of rays has been well parted from 

 those of other kinds, it has afterwards obstinately retained its colour, 

 notwithstanding my utmost endeavours to change it. I have refracted 

 it with prisms, and reflected it with bodies, which in day-light were 

 of other colours; I have intercepted it with the coloured film of air 

 interceding two compressed plates of glass; transmitted it through 

 coloured mediums, and through mediums irradiated with other sorts 

 of rays, and diversely terminated it; and yet could never produce any 

 new colour out of it. It would, by contracting or dilating, become 

 more brisk, or faint, and by the loss of many rays, in some cases very 

 obscure and dark; but I could never see it change in specie. 



4. Yet seeming transmutations of colours may be made, where 

 there is any mixture of divers sorts of rays. For in such mixtures, 

 the component colours appear not, but, by their mutual allaying each 

 other, constitute a middling colour. And therefore, if by refraction 

 or any other of the aforesaid causes, the difform rays, latent in such 

 a mixture, be separated, there shall emerge colours different from the 

 colour of the composition. Which colours are not new generated, but 

 only made apparent by being parted; for if they be again entirely 

 mixed and blended together, they will again compose that colour, 



