C 3081 ) 
Bat to retarn from this digreflion, I told you^ that Light is not 
fimilafj or homogenealjbut confifts of difform R.ays,foaie of which 
are more refrangible than others : So thr?t or thofc^ which^re 
ahke incident on the fame medinm^ fonie fliail be more refrafted 
than others, and that not by any virtue of the glafs^ or other ex? 
ternal caufe, but from a predifpofition ^ which every particular 
Ray hath to fuffer a particular degree of Ref radtion, 
I fliall now proceed to acquaint you with another more notable 
difFormity in its Rays , wherein the Origin of Colours is unfolded : 
Concerning which I fliall lay down the DoUrine firft, and then, for 
its examinationj give you an inftaoce or two oi iht Experiments^ 
as a (pecinien of the reft. 
The Dodlrieey^ will find C3mprehended and illuftrated m 
the following propofitions* 
1. As the Rays of light differin degrees of P^efrangibility, io 
they alfo differ in their difpoficion to exhibit this or that parcicii- 
lar colour. Cplours are not Salifications of Light ^ derived from 
RefradlionSjOr Reflections of natural Bodies (?.s 'tis generally b:« 
lieved^) but Originahnd cannate proper tie t.wWxch. in divers Rays are 
divers. Some Rays are difpofed to exhibit a red colour and no 
other 5 fome a yellow and no olher^ lome a green and no othcr^ 
and fo of the reft. Nor are there only Rays proper and part-xu^ 
!ar to the more eminent colours^ but even to all their intermediate 
gradations. 
2. To the fame degree of Refrangibilicy ever belongs the fame 
colour, and to the fame colour ever beloiigs the fame degree of 
Refrangibilicy. The leajl llefrangibh Rays are all difpofed to ejr« 
hibit a J{ed colour, and contrarily thofe Rays, which are difpofed 
to exhibit a colour, are all the leaft refrangible : So the mojl 
refrangible Rays are all difpofed to exhibit a dz^^ Violet-Colour.mA- 
contrarily thofe which are apt to exhibit fuch a violet colour^ are 
allthemoft Refrangible. And fo to ail the ioteraiediate colours 
in a continued feries belong intermediate degrees of refrang bili- 
ty» And this Analogy 'cwixt colours, and refrangibiliry, is very 
precife and ftricil 3 the Rays always eitlier exactly agreeing iii: 
bothj or proportionally difagreeiog isi both. 
The fpecies of colour, and degree of Refrangibility proper 
to any particular fort of Rays^ is not mutable by Refradtion^ nor 
by Refled:ion from natural bodies, nor by any other cuufej 
I could yet obferve'. When any one fort of Rays hath been well 
parud 
