London May 2. 72.


Having sent away your answer to the Iesuit Pardies, after it had been read at our Society as well as your letter containing your observations relating to Sir R. Moray's proposals; I receiued a printed account from Paris, which relateth to your Telescopes, and pretends to haue lighted upon a refinement of them. This I thought myself obliged to impart to you, that you might consider it, and compare it with what Mr Gregory, the Scot, hath printed concerning it, in his optica promota Ann. 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 a communiqué la figure d'un Telescope, qui est presque 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, qui 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 the confident assertions of this Author, as I am apt to belieue, you will make good your Theory of light; which some begin to lay more weight upon now, than at first. Howeuer, I shall suggest, that when your answer to Mr Hooks and the Iesuit Pardies objections shall be thought fit to be printed, the names of the Objectors, especially if they desire it may be so, be omitted, and their objections only urged: since those of the R. Society ought to aime at nothing, but the discovery of truth, and the improvement of knowledge and not at the prostituting of persons for their mis-apprehensions or mistakes.

Our Treasurer was not present at our meeting; so that I could not deliuer him your quarters payment: which I shall doe the first time I find him there; and then send you his acquittance; being


your faithful servant



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



© 2020 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

Privacy Statement

  • University of Oxford
  • Arts and Humanities Research Council
  • JISC