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By this you may perceive, That the Errors of .the Refeacting Convex areso far from being leis, that they are more than 16 times greater than .the likeErrors of the Reflecting Concave, elpecially in great Apertures ; and that with-tiut rdpectto the HeterogEneaus Constirution of Light. So that, howeverthe contrary Suppositfon Tnigjht malte the Author of thde Animadversions re-ject Reflexions as uselels for the promoting of Opticks ; yet l must forthis, as well as other Considerations, prercr thera in the Theory bssoreRefractions.

VVhether the Pur ahoi« be more difficult to describe than the Hyporbola,, orV.llipsu , may be a Queere ; But Ifee no absolute necellity of endeavouringafter any of their Delcriptions. For if Metals can be grountj truly Spherici),they will bear as great Apertures,as I believe Men will be well able to commu-nicate an exact Polisti to. And for Dioptrique Teleseopcs, 'I told you, Thatthe difficulty consisted not in the Figure of the Glase, but in the'Difformityof Refractions ; which if it did not, I could tell you a bester and moreeasie remedy than the ufe of the Conic Seil Uns.

3. We see that a Picture made by an Object Glaseof <11 Foot in a dark bbjtfi'mtv&yRoom,'istoo Distirict, and too well Defined, to be produced by Rays, that •• • ,* •*„should stray the yoth part of the Aperture. n. 9 . j. o

To take away this difficulty, I must acquaint you, That thoUgh I put b

the greaftest Lateral Error of the Rays ffom<one anotber to he about ofthe Gkfs’s Diameter ; yet their greater Error' from the Points on whieh theyöiight to fall, willIbe but-J- of that Diameter: And -then, that-the Rays,whöse Error is so gfeat, arc but very sew in cotnpanson to thole, whieh areRefracted more juitly ;' for ' the' Rays which fall upon the-middleFarts of theGlase, are Refractcd -with lirstitäent Exactnese, as also are those - that fallffear the Perimeter and hate a rtiean degfee of iRefrangibtlicy; so that- thereremain only the Rays, which ! füll- near the'Perimeter and are most or leaftRetrangiblc, to caule any sensible Confusion in the Pictuce. And theso are yetlu’miRh-further weakned by the greater Ipace,' through . which they are-fcat-rerkl, that'the Light which falls on the d\re Point, isi infiniedy rnore'Dcolcthan that which falls on any Other Point rownd about it. And -by this

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