Lislrnments of the Anllents. 1 89 



though, after Zucchi, and before Newton, father Mer&m/ie 

 had proposed to Descartes the idea of using concave mirrors 

 in making telescopes, and although James Gregory and 

 Cassegrain had given descriptions of reflecting telescopes, I 

 <lo not find any mention of such a telescope having been 

 executed before that of Newton*. 



34. " Notwithstanding the happy success of the Newto- 

 nian telescope, and the great advantages expected from it, 

 it was a long time neglected, and there appeared to be little 

 earnestness to bring it into use. It was only some years ago 

 that this instrument came into vogue, and was commonly 

 used with effect f. And how many other fine discoveries 



* " It must be acknowled that Mr. James Gregory, of Aberdeen, was 

 the first inventor of a reflecting telescope. Mr. Gregory describes this tele- 

 scope at the end of his Optica Promofa. published in 1663 » ami was ied to 

 the invention of it, not by the consideration of the different refrangibility 

 of rays, which was not then known, but by an inconvenience he foresaw 

 would follow from an hyperbolic object-glass/" Dr. S's Compi. Syst. of 

 Optics, Rem. 135. " Mons. Cassegrain' s is not pretended to have been. 

 contrived before the year 3672, and Sir I. Neiutons was contrived in 

 j666, and executed in 1670, or at farthest finished in 1671. Besides, 

 M. Cassegrain s differs in nothing from Gregory's, but that he would have 

 the small metal to be convex, which Gregory makes concave, and there- 

 fore his instrument seems only to be Gregory's disguised." Desagulie.rs's 

 .Append, to the 2d ed.of Dr. Browne's Translation of Dr. Dwvid Gregory's 

 (the nephew of James) Elem. Caiopt. et Diopt. p. 234. There is no 

 reason to suppose that J. Gregory knew any thing of the discovery of 

 Zucchi - y for, in the Pref. to bis Opt. Prom, he complains that he was not 

 timely apprised of those of Descartes, on account of the bad supply of 

 new mathematical books, in the otherwise well-furnished public library 

 at Aberdeen. Nay, Descartes himself did not (not to say could r.ot, 

 though Mersenne did) know of the diseovery of Zucchi, who, as appears 

 above, did not pulxlish it till 1652; whereas Descartes'* correspondence 

 with Mersenne took place in 1639, though it was not printed rill 1666, 

 three years after J. Gregory published his Opt. Prom. (See Descaries's 

 letters, vol. ii.) Add to this, that Mersenne proposed to Descartes his 

 idea of a reflecting telescope in a way so very unsatisfactory, as to induce 

 the latter to endeavour to convince him of its fallacy. If it should be said 

 that J. Gregory might have got the hint from Zucchi in Italy, the answer 

 would be easy : he published his Optica Promota in London in 1663, the 

 24th year of his age; but did not go abroad till 1665. In 1667 he pub- 

 lished, at Padua, his V(ra Circu/i et Hyperbola? Qrtadratura ; and in 1668, 

 at Venice, his Geometric Pars Universalis. — See Dr. Hutton's Dictionary, 

 articles Gregory and Telescope .—Translator. 



f From our author's maimer of expressing himself here, it would seem 

 that reflecting telescopes did not come into use in France nearly so soon 

 as in this country. For Dr. S , in his Compl. Syst. of Opt. Rem. 136, 

 says, t4 These telescopes were first brought to perfection in prarrice about 

 the year 1719 by the great ingenuity and industry of Mr. John Hadl-yi 

 Sir fsaar Newton* f first, and Mr. Gregory's soon after." "My original, as 

 already observed, was printed in 1763.-^ Translator, 



are 



