<36r> < insertion from the top of f 36r >

Mr Newtons Letter to Mr Oldenb.
containing some Advertisements about his
Reflecting Telescope.

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Read Mar: 21: 71

Enter'd LB. 5. 364.

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Sr

In my last letter I gave you occasion to suspect that the instrumnt wch I sent you is in some respect or other indisposed, {illeg} \or/ that the metalls are tarnished. And by yor letter March 16 I am fully confirmed in that opinion. For whilest I had it, it magnified represented the Moon in some parts of it as distinctly as other Telescopes usually doe wch magnify as much as that. {illeg}|Ye|t I very well know that that instrument hath its imperfections both in the composition of the metall & in its bei{illeg}|n|g badly cast as you may perceive by a scabrous place nere {sic} the middle of the {midd|eta|le} of the metallon ye polished side, & also in the figured|e| of that metall neare that scabrous place. And in all those respects that instrument is capable of further improvement{.}

You seem to intimate that the proportion of 38 to 1 ho{lds} \holds/ onely for its magnifying objects at small distances. But if for such distances suppose 500 foot it magnify at that rate, by the rules of opticks it must for the greatest distance imaginable magnify more then 3734 to 1 wch is so insensible a diminishing that I it may be even then put as 38 to 1.

I told you that here is anot{illeg}|h|er instrument made like the former wch doth very well. Yesterday I compared it wth a six foot Telescope & found it not onely to magnif{illeg}|y| more but also more distinctly. And to day I found that at a {illeg} hundred foot distance I could reade in one of the Philosophicall Transactions p\l/aced in the sun's light at a hundred foot distance, & that at a hundred & twenty foot distance I could discern some of the words. When I made this tryall its aperture (defined {illeg} next the eye) was equalent {sic} to more then an inch and a th{illeg}|ir|d part of the object metall. This I thought good to inform you of because it may be of some use to those that shall endeavour any thing in reflect|x|ions. Fo{illeg}|r| hereby they will in some measure be enabled to judg of the goodness of their instruments{.} &|A|nd for this end you may annex these observations made wth this last instrument, t{illeg}|o| the description of it in the Transactions of this Month. But my answer to Mr Hooks observations will not be ready for then, because I intend to annex to that answer some further explications of the Theory, wch I shall not have leisure to do this week or fourtnight. Sr I am in hast

Yor Faithfull servant.

I. Newton

March 19th. 1671.

<36v> [Editorial Note 1]

These

For {illeg}|H|enry Oldenburg Esq
at his ho{illeg}|u|se neare the
middle of the old Pall-mail
in Westminster

London

2

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Rec. March. 20. 71.

Answ. March. 23. comm. ye
Comet and sub cap
Cygni from Hevel.

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i.e. if ye \{bent}{lens}/ axis were direct {illeg}|w|ere accounted streight,

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[Editorial Note 1] Envelope text written upside down on page

© 2017 The Newton Project

Professor Rob Iliffe
Director, AHRC Newton Papers Project

Scott Mandelbrote,
Fellow & Perne librarian, Peterhouse, Cambridge

Faculty of History, George Street, Oxford, OX1 2RL - newtonproject@history.ox.ac.uk

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