A discourse on the invention and improvements of the reflecting telescope. Delivered at the anniversary meeting of the Royal Society, November 30, 1777. / By Sir John Pringle, Baronet, President. Published at their request.

  • John Pringle
Date:
MDCCLXXVIII [1778]
Catalogue details

Licence: Public Domain Mark

Credit: A discourse on the invention and improvements of the reflecting telescope. Delivered at the anniversary meeting of the Royal Society, November 30, 1777. / By Sir John Pringle, Baronet, President. Published at their request. Source: Wellcome Collection.

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    [ !3 ] Me from objeCl-glaJfes, which was the obliquity of both their fur faces, which vitiated the refraClion of the rays that pafs towards the fides of the glafs, and did more hurt than men were aware of. Again, that by the mere reflection of the metalline fpeculum there zvere not fo many rays lofl as in glafles, which reflected a conflderable quantity by each of their furfaces, and befldes intercepted many of them by the ohfcurity of their matter..... flbat the main bufinefs would be, to find a matter for this fpeculum that would bear as good and even a poli/h as glaj's. haflly, he believed that Mr. Newton had not been without confldering the advan¬ tage which a parabolic fpecidum zvould have above a fpheri- calone in this conflruCtion\ but had defpaired, as he him- felf had done, of working other furfaces than fpherical ones with due exaCtnefs(,). Huygens was not fatisfied with thus exprefling to the Society his high approbation of the late invention, but drew up a favourable account of the new telefeope, which he caufed to be publifhed in the Journal des Scavans, of the year 167 2, and by that channel it was foon known over Europe. But how excellent foever the contrivance was; how' well foever fupported and announced' to the public; yet whether it was that the artifts were deterred by the dif¬ ficulty . (i) Phil. Tranf, ns 8i,