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1 ftiall now proceed to acquaint you with another more Notable DiffornütyIn Its Rays, wherein the Origin of Colours is unfolded: concerning whichI (hall lay down the Doctrine first, and then for its Examination give you anInstancc or two of the Experiments, as a Specimen of the reit.

The Doctrine you will find comprehended and illustratcd in the followingPropositions.

i. As the Rays of Light differ in Degreesof Refrangibility, so they also dif-fer in their dilposition to exhibit this or that particular Colour. Colours arenot Qualifications of Light, deriv’d from Refractions, or Reflections of Na-tural Bodies (as ’tis generally bclievedj but Original and Connate Properster,which in divers Rays are divers. Some Rays are dilpoled to exhibit a Red Colourand no other; some a Yellow and no other, some a Green and no other, andso of the reff. Nor are there only Rays proper and particular to the moreEmiment Colours, but even to all their Intermediäre gradations.

2 .. To the läme degree of Refrangibility ever belongs the lame Colour,and to the lame Colour ever belongs the (amc degree of Refrangibility. TheJcast Refrangible Rays are all dilpoled to exhibit a Red Colour, and cotnrari-ly thole Rays which are dilpoled to exhibit a Red Colour are all theleast Refrangible: So the most Refrangible Rays are all dilpoled to exhibit adeep Violet Colour, and contrarily thole which are apt to exhibit lücha Violet Colour are all the most Refrangible. And so to all the Inter-mediate Colours in a continued Series belong Intermediäre Degrees of Refran-gibility. And this Analogy ’twixt Colours and Refrangibility is very p recisoand strich ; the Rays always either exactly agreeing in both, or proportionallydilägreeing in both.

3 . The Species of Colour, and Degree of Refrangibility proper to any par-ticular sort of Rays, is not Mutable by Refraction, nor by Reflection from Na-tural Bodies, nor by any other caule that I could yet oblerve. When any onesort of Rays hath been well parted from thole of other kinds, it hath after-wards obstinately retained its Colour, notwithstanding my utmost endeavoursto change it. I have Refracted it with Prilms, and Reflected it with Bodies,which in day light were of other Colours; 1 have intercepted it with the Co-loured film of Air, interceeding two compreffed Plates ot Glals, tranfmittedit through Coloured Mediums, and thro’ Mediums Irradiated with other sortsof Rays, and diverfly terminated it; and yet could never produce any newColour out of it. It would by contracting or dilating become more brisk,or faint, and by the lols of many Rays, inlbme Casos very obscure and dark;but 1 could never fee it chang d in Specie.

4 . Yet sceming tranfmutations of Colours may bc made, where there is anymixture of divers sorts of Rays. For in such Mixtures, the component Co-lours appear not, but, by their mutual allaying each other, constitute a mid-ling Colour. And therefore, if by Refraction, or any other of the aforelaidCaules, the Difform Rays, latent in such a mixture, be feparated, there (hallEmerge Colours different from the Colour of the Compofition. Which Co-lours are not New generated, but only made apparent by being parted; for