Cambridg. Sept 21 1672.

SrSir

That letter wchwhich you directed to Stoake in answer to mine from thence I received not as I told you, formerly, but your last wherein you repeated the contents of that I received, & am troubled ytthat I have answered it no sooner; especially since I was obliged to thank you for yethe Transactions of July, & more particularly for yoryour elegant translation of my Letter published in them, & for the trouble you was pleased to take upon you in inquiring of Mr Cock about his Telescopes.

To comply wthwith yoryour intimation of communicating ExptsExperiments proper for determining yethe Quæres wchwhich ytthat Letter conteined I drew up a series of such ExptsExperiments on designe to reduce yethe Theory of colours to Propositions & prove each Proposition from one or more of those ExptsExperiments by the assistance of common notions set down in the form of Definitions & Axioms in imitation of the Method by wchwhich Mathematitians are wont to prove their doctrines. And that occasioned my suspension of an answer, in hopes my next should have conteined the said designe. But before it was finished falling upon some other buisiness, of wchwhich I have my hands full, I was obliged to lay it aside, & now know not when I shall take it again into Consideration. However if the Answer to Mr Hooks Considerations will conduce to the determination of any of those Quæres (as in some particulars I think it will) you may if you think fit, publish it; To wchwhich end I desire you to mitigate any expressions that seem harsh, that its publication as you intimated may be done to common satisfaction. And though I intend at present nothing further for the publick, yet if to any of your private acquaintance that endeavour to satisfy themselves by an experimentall determination of those Quæres, Experiments sufficient to determin them all occur not; upon your intimation of the particulars wchwhich they stick at, I shall for yoryour sake doe my endeavour as much as I can in short to supply what they desire

I have not yet perused those two books you mention. But by yoryour description of yethe first in the Transactions it seems to contein a Doctrin most highly probable, & in the latter I expect to meet wthwith many things as improbable. And then that particular wchwhich you mention I know not what can be more difficult.

I am sorry for the miscarriage of yoryour afforesaid letter & blame my selfe for my Postscript suspecting that may have occasioned in yorsyours what you would not have fall into other hands then those of

SrSir

YorYour humble Servant

Newton.

These

To Henry Oldenburg Esqꝫuire at his house about the middle of the old Pall-Mail in

Westminster

London.

Rec.Received Sept. 23. 72

2 Answ.Answered Sept. 24.

Rec.Received Sept. 223. 72. Answ.Answered Sept. 24. of Salvetti's makging his Telescope: to move him to prosecute it, as well as to put out of doubt his doctrine of Colors. Of Th. Huyck. Of Hugens his sense about his doct.doctrine of Colors.