Isaac Newton to Henry Oldenburg

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                                been now said of white. And so the necessity of all colours to produce white 
might have appeared by y<sup>e<\sup> experiment pag 5097 where I say that if any 
colour at y<sup>e<\sup> Lens be intercepted y<sup>e<\sup> whiteness (wch is compounded of them all)
will be changed into (y<sup>e<\sup> result of) the other colours.
However, since there seems to have happened some misunderstanding between 
us, I shall indeavour to explain my self a little further in these things according to 
the following method.
<u>Definitions <\u>
1. I call that Light homogeneal, similar or uniform whose rays are equally 
2. And that heterogeneal whose rays are unequally refrangible.
Note. There are but three affections of light in w<sup>ch<\sup> I have observed its rays 
to differ viz: Refrangibility, Reflexibility & Colour, & those rays w<sup>ch<\sup> agree in
refrangibility agree also in the other two & therefore may well be defined homo-
general: especially since men usually call those things homogeneal w<sup>ch<\sup> are so 
in all qualities that come under their knowledge, though in other qualities that their 
knowledg extends not to there may possibly be some heterogeneity 
3. Those Colours I call simple or homogeneal, which are exhibited by homo-
geneal light.
4. And those compound or heterogeneal w<sup>ch<\sup> are exhibited by heterogeneal light.
5. Different colours I call not only the more eminent species, red, yellow, green, blew 
purple, but all other <s>gradations <\> the minutest gradations: much after y<sup>e<\sup> same manner that 
not onely the more eminent degrees in musick but all y<sup>e<\sup> least gradations are esteemed 
different sounds.
<u>Propositions <\u>
1. The sun’s light consists of rays differing by indefinite degrees of refrangi-
2. Rays w<sup>ch<\sup> differ in refrangibility, when parted from one another do proportionally 
differ in the colours w<sup>ch<\sup> they exhibit. These two propositions are matter of fact.
3. There are as many simple or homogeneal colours as degrees of refrangibility.
For to every degree of refrangibility belongs a different colour by Prop: 2. And 
that colour is simple by <u>Def.:<\u>1, & 3.
4. Whiteness <s>such as is <\s> in all respects like that of the Sun’s immediate light & of all y<sup>e<\sup> usuall 
objects of o<sup>r<\sup> senses cannot be compounded of two simple colours alone. For
such a composition must be made by rays that have only two degrees of refran 
gibility by <u>Def<\u>. 1 & 3; & therefore it cannot be like that of the same light 
<u>Prop<\u>. 1; Nor for y<sup>e<\sup> same reason like that of ordinary white objects.
5. Whiteness in all respects like that of the Sun’s immediate light <s>may <\s> cannot be 
compounded of simple colours, <s>there are requisite <\s> without an indefinite variety of them. For in
such a composition there are requisite rays indued w<sup>th<\sup> all y<sup>e<\sup> indefinite degrees of 
refrangibility by <u>Prop<\u>. 1. And these infer as many simple colours, by <u>Def<\u>. 1, & 3. &
<u>Prop<\u>. 2 & 3
To make these a little plainer, I have added also the Propositions that 
6. The rays of light do not act on one another in passing through the same medium. This appears by several passages in y<sup>e<\sup> <u>Transactions pag<\u> 5097, 5098,
5100, & 5101, & is capable of further proof.
7. The rays of light suffer not any change of their qualities from refraction 
8. Nor afterwards from the adjacent quiet <u>Medium <\u>. These two Propositions 
are manifest de facto in homogeneal light, whose colour & refrangibility is not at all
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Isaac Newton
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Isaac Newton to Henry Oldenburg, 1673. From The Royal Society, EL/N1/47



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