Isaac Newton to Henry Oldenburg

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                                changeable either by refraction or by the contermination of a quiet Medium. And as for 
heterogeneal light, it is but an aggregate of severall sorts of homogeneal light no one 
sort of w<sup>ch<\sup> suffers any more alteration then if it were alone because the rays act 
not on one another by <u>Prop<\u>. 6. And therefore the aggregate can suffer none. The (?)
two <u>Propositions <\u> also might be further proved apart by experiments, too long to be here
9. There can no homogeneal colours be educed out of light by refraction 
w<sup>ch<\sup> were not commixt in it before: Because by <u>Prop 7<\u> & 8, Refraction 
changeth not y<sup>e<\sup> quality of y<sup>e<\sup> rays, 
but only separates those w<sup>ch<\sup> have divers 
qualities, by means of their different Refrangibility 
10. The sun’s light is an aggregate of an indefinite variety of homoge-
neal colours: by <u>Prop<\u> 1, 3, & 9. And hence it, that I call homogeneal 
colours also primitive or original. And thus much concerning colours.
<s>M. Hugens <\s> Mons<sup>r<\sup> N. has thought fit to insinuate y<sup>t<\sup> y<sup>e<\sup> aberration of rays (by their different 
refrangibility) is not so considerable a disadvantage in glasses as I seemed to <s>make<\s> be
willing to make men Beleive when I propounded concave mirrors as y<sup>e<\sup> only hopes
of perfecting Telescopes.  But if he please to take his pen & compute the errors 
of a Glass & Speculum that collect rays at equall distances, he will find how 
much he is mistaken, & that I have not been extravagant, as he imagins, in
preferring reflexions. And as for what he <s>adds<\s> says of y<sup>e<\sup> difficulty of y<sup>e<\sup> praxis 
I know it is very difficult, & by those ways w<sup>ch<\sup> he attempted it I beleive it unpracticable.
But there is a way insinuated in y<sup>e<\sup> <u>Transaction pag <\u> 3080 [illegible]
by w<sup>ch<\sup> it is not improbable but that as much may be done in large Telescopes,
as I have thereby done in short once, but yet not without more than ordinary diligence & curiosity.
<s>Pray w<sup>th<\sup> these Notes return my thanks to M. Hugens for his book.
By a former letter of yo<sup>rs<\sup> I was a little dubious whether M. Slusius might not appre 
hend, by w<sup>t<\sup> you wrote to him concerning me, y<sup>t<\sup> I pretended to his Method of Drawing tangents;
untill I understood by M. Collins y<sup>t<\sup> you signifyed to him y<sup>t<\sup> you thought it here of a later 
date. For it seems to me that he was acquainted w<sup>th<\sup> it some yeares before he printed 
his Mesolabum & consequently before I understood it. But if it had been otherwise yet since he
first imparted it to his friends & y<sup>e<\sup> world, it ought deservedly to be accounted his. As
for y<sup>e<\sup> Methods they the same, though I beleive derived from different prin 
ciples. But I know not whether his Principles afford it so generall as mine w<sup>ch<\sup> extends to Equa 
tions affected w<sup>th<\sup> surd terms, w<sup>th<\sup>out reducing them to another form. But if you please let this 
<s>The incongruities you speak of I pass by. But I must as formerly, signify to you y<sup>t<\sup> I intend 
to be no further sollicitous about matters of Philosophy. And therefore I hope you will [illegible]
if you find [illegible] doing any thing more in y<sup>t<\sup> [illegible] you will 
favour me in my determination [illegible] so far as you can  conveniently my objections 
or the philosophicall [illegible]. For your prefer about my [illegible]
[illegible] I thank you. But I would not have you trouble yourself to get them excused if you have not 
done so already. And now being tired with this long letter, I must in [illegible]
Yo<sup>r<\sup> humble ServantI
I. Newton <\s>

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Isaac Newton to Henry Oldenburg, 1673. From The Royal Society, EL/N1/47



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