Letter from Newton to Henry Oldenburg, dated 29 January 1671/2

<14r> < insertion from the left margin >

M^r An Extract of M^r Newtons letter to M. Old. about the Comp Metallin Composition for an Object-speculum to his Reflecting Telescope

< text from f 14r resumes >

Jan 29^th. Cambridg. 16$\frac{71}{72}$

S^r

|Ph. Trans. N. 81. p. {illeg}|4|006.| Not having tryed many proportions of the Arsenick & Metall I am not assured w^ch is absolutely best, but there may conveniently be used any quantity of Arsenick equalling in weight between a sixt & eight part of y^e Copper. A greater proportion makes the metall brittle.

The way w^ch I used it is this. I first melted the Copper alone, then put in y^e Arsenick, which being melted I stirred them a little together, bewaring in the meane time that I drew not in breath neare the pernicious fumes. After that I put in the Tin, & again, so soon as that was melted, w^ch was very suddenly, I stirred them well together, & immediately powered them of.

I know not whether by letting them stand longer on y^e fire after the Tin {illeg}|w|as melted, a higher degree of fusion would have made the metall porous, but I thought that way I proceeded to bee safest. In that metall w^ch I sent to London there was noe Arsenick, but a small proportion of silver: as I remember $1^{\mathrm{s}}$ {illeg} in $℥\mathrm{iij}$ of metall. But I thought the silver did as much harm in making the metall soft & so lesse fit to bee polished, as good in rendering it white & luminous. At another time I mixed Arsenick $℥\mathrm{j}$ Copper $℥\mathrm{vj}$ & Tin $℥\mathrm{ij}$. And this an {illeg}|A|cquaintance of mine hath polished better then I did the other. |]|

The publishing a description of the Telescope in the Transactions I wholly leave to your pleasure, being willing to submit my private considerations in any thing that may bee thought of publick concernment. |[|I have sent you by the bearer John Stiles 40^s|]| for admission money. And I hope I shall get some spare howers to send you <14v> also suddenly that accompt w^ch I promised in my last letter. In the meane time I rest

Yo^r very faithfull S^rvant

I. Newton.