<459r>

## Cambridge Dec. 7. 1675.

Sr

I have sent you ye papers I mentioned, by Iohn Stiles. Vpon reviewing them I find somethings {sic} so obscure as might have deserv'd a further explication by schemes, & some other things I gues will not be new to you though almost all was new to me when I wrote them. But as they are I p{illeg}|ho|pe you will accept of them though not worth ye ample thanks you sent. I remember in some discourse wth Mr Hook I happend to say yt I thought light was reflected not by ye parts of {illeg}|g|las, water, air or other sensible bodies, but by ye same {illeg}|co|nfine or superficies of ye æthereal Mediums, wch refracts it, ye rays finding some difficulty to get through it in passing out of ye rarer \denser/ into ye denser \rarer Medium/, & a greater difficulty in passing out of ye rarer into ye denset|r|; & so being either refracted or reflected by that superficies, as ye circumstan{illeg}|c|es, they happend to be in at their incidence, make 'em able or unable to get through it. And for confirmation of this I said furth{illeg}|e|r, that \I thought/ ye reflexion of light at its tending out of glas into air would not be diminisht or weakend by dra{illeg}|wi|ng away ye air in an a|A|ir-Pump, as {illeg} it ought to be if they were ye parts of air that reflected. And added yt I had not tryed this Experimt, but thought he was was not unacquainted wth notions of this kind. To wch he replyed yt ye notion was new & he would ye first opportunity try ye experimt I propoundd {sic} But upon reviewing ye papers I send you, I found it there set down for tryed; wch makes me recollect yt about ye time I was writing those papers I had occasionally observ'd in an Air-pump here at Christs College, yt I could not perceive ye reflexion of ye inside of ye glas diminished in drawing out ye Air. This I thought fit to mention least my former forgetfulnes through have|i|ng long laid aside thoughts on these things, should seem to make me seem to have set down for certain what I never tryed

Sr I had formerly purposed never to write any Hypothesis of light and colours, fearing it might be a means to ingage me in vain disputes: but I hope a declard resolution to answer nothing that looks like a controversy (unles possibly \at my own time/ upon some other by occasion) may defend me from yt fear. And therefore considering that such an Hypothesis would much illustrate ye papers I send you promisd to send you & having a little time this last week to spare: I have not scrupled to describe one so far as I could on a sudden recollect my thoughts about it, not concerning my self wha|e|t|her| \it/ shall be thought {p}robable or improbable so it do but render ye papers I send you {and} others sent formerly more intelligible. You may see by ye <459v> scratching & interlining 'twas done in hast & I have not had time to get it transcribd, wch makes me say I rese{illeg}|ver| {sic} a li{illeg}|b|erty of adding or altering it, & desire yt you would return those & ye other papers when you have done wth them. I dou{illeg}|b|t there is too much to be read at one time but you'le soon know how to order that The Hypothesis of these expe do but And At ye end of ye Hypothesis you'l see a paragraph to be inserted as is there directed; I should have \added/ another or two but I had not time. But such as it is. I hope you will accept it. Sr I am

Yor humble servant

Is. Newton.

Rec. Dec. 8. 75

Began to read it before ye Society Dec. 9.

Answ. this letter Dec. 11. and desired his mission to retain a copy of all these papers.

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