<10r>

London May 2. 72.

Sir,



Having sent away yr answer to ye Iesuit Pardies, after it had been read at our Society {illeg}|a|s well as yr letter containing yr observations relating to Sr R. Moray's proposals; I receiued a printed account from Paris, wch relateth to yr {illeg}|T|elescopes, and pretends to haue lighted upon a refinemt of yt|ym|. This I thought myself obliged to impart it to you, yt you may|ig||ht| consider it, and compare it wth what Mr Gregory, the Scot, hath printed concerning it, in his optica promota {illeg}|A|nn. 1663 pag. 92. 93. 94: and thereupon let me know what answer to return to those Parisian Refiners; who speake thus:

Il y a environ mois, que M. Cassegrain {illeg}|a| communiqué la figure d'un Telescope, qui est pres semblable à celuy de M. Newton, et qu'il a inventé; mais que ie trouue plus spirituel. Ie vous en fais icy la description.

FigureABCD est vn fort tuyan, dans le fonds duquel il y a un grand miroir Concave Cd, percé en son milieu.

F est un miroir convexe, desposé de telle maniere, eu esgard à sa convexité qu'il refleschit les especes, qu'il recoit du grand miroir, vers le trou au milieu dc Cd; ou'il y a un Oculaire, au travers duquel on regarde.

L'avantage, que|i| se trouue dans cet Instrument sur celuy de M. Newton, est, 1. que l'embouchure ou l'ouuerture du luyan AB, peut estre de telle grandeur qu'on vendra; et <10v> par consequent que l'on aura bien plus de rayons sur le miroir concaue, que sur celuy de M. Newton. 2. La reflexion des rayons sera tres naturelle, puisqu'elle se fera sur l'Axe mes{ur}e, et consequemment plus vive. 3. La vision en sera d'autant plus agreable, qu'on ne sera ponit incommo, de' du grand iour, à cause du fond CD, qui couvre tout le visage. Outre qu'on aura monis de peine à descouvrir les Objects, que dans celle de M. Newton.

So far the French Iournal. I am of opinion, you will find cause to controle these confident assertions of the|i|s Author, as I am apt to belieue, you will make good yr Theory of light; wch some begin to lay more weight upon now, than at first. Howeuer, I shall suggest, yt when your answer to Mr Hooks and ye Iesuit Pardies objections shall be thought fit to be printed, ye names of the Objectors, especially if they desire it may be so, be omitted, and their objections only r{illeg}ed and urged: since those of the R. Society aime ought to aime at nothing, but the discovery of truth, and ye improvemt of knowledge \and/ not at all the prostituting \of persons for/ their mis-apprehensions or mistakes. {of} {illeg} s{illeg}

Our Treasurer was not present at our meeting; so yt I could not deliuer him yr quarters paymt: wch I shall doe the first time I find him there; and then send you his acquittance; being

Sir

yr faithful servt

Oldenburg.

<11v>

To his honor'd friend Mr Isaac Newton Professor of the Mathematicks, in Trinity Colledge in the University of

Cambridge

2

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Professor Rob Iliffe
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Scott Mandelbrote,
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