Mifiellanea Curiofa. 103 



Refraction of the . utmoft Ray on the other end* 

 fixty nine parts, fo thai: the difference is 'about a 

 twenty fourth or twenty fifth part of the whole 

 Refraction. And conlequcntly the Object glafe- 

 of any Telefcope cannot collect all the Ray?, 

 which come from one point of an Object fb as 

 to make them convene at its Ftcus in lefs room 

 than In a Circular (pace, whofe Diameter is the 

 fiftieth part of the Diameter of its Aperture ; 

 which is an irregularity, jfpme hundred of times 

 greater, than a circularly hgurd Lens, of fo fmall 

 a lection as the Object-glaiTes of long Telefcopes 

 . are, would caufe by the unfitnefs of its Figure, 

 were Light uniform. , 



This made me take Rj;flcBions into Con fide ra- 

 tion, and finding therri regular, fb that the 

 Angle of Reflection of all forts of Rays was 

 equal to their Angle ^of Incidence • I underllood, 

 that by their mediation, Optick Inftruments 

 might be brought to any degree of Perfection 

 imaginable, provided a Subftance could 



be found, which would polifh as finely as Glafs, 

 and. reflctt as- much Light as G%^ra^finTts\ and 

 the art of communicating to it a Parabolick Pi» 

 gure be alfo attaint!. But there leem'd very great 

 Difficukities, and I have almoft thought them in- 

 fuperable, when I further confider'd, that every 

 Irregularity in a reflecting Superficies makes the 

 Rays ftray five or fix times mere out of their due 

 courie, than the like Irregularities in a refracting 

 one : So that a much greater Cm iofiry would be 

 here requifite, thaa in Figuring GlafTes for Re- 

 fraction. 



Amidft thefe Thoughts I was Lrc'd from Cam- 

 bridge by the Interyenirg Plague, and ir was 

 more than two Years before / proceeded .further. 

 But then baying ibougHt on a tender way of po- 

 1. n ' " * "4 V 1 liming, 



