Cffi) 
An Account 
Of the Invention of Grinding Optick and 'Barning -Ghfts of * 
Figure not-Sphertcail, produced before the R, Society. 
^TpHe Ingenious and laduftiious Francis Smethmck E quire \ 
\ Fellow of the R. Society, having for divers years painfully 
fearch'c after the way of Grinding G\*&z$ not- Spheric alf affirms, 
that at length he hath now found it: for the proof of which, 
he lately .viz. February 2 7. 166$$ produced before the {aid So- 
ciety certain Specimina of that Invention , which were a Te- 
le f cope ^ a Reading-, and two jBWning-GliSts. 
1 he T elefccpv was about four toot long, furnifht with four 
Glaffes,whereof the thxttOcular ortes^Pianc-convexe^wereof this 
newly-invented not spheric all Figure, and the fourth a Spheric all 
Objedl-glafs. This being compared with a Common^ yet very 
good Telefcope, longer than it by about 4. inches, and tuin'd to 
feverall objeds, was found by thofe of the fa id Society , chat 
look'd through them both, to exceed the other in good nt fie, by 
taking in a greater angle, and repreftnting the Obje&s more ex- 
a&Iy in their refpedive proportions, mi enduring a greater 
Aperture, free from colors. 
The Reading Glaffe, of the fame Figure, being compared with 
a common SphericAll-Ghfte, did far excel! it, by magnifying the 
Letters, to which it was spplyed, tip to the ve:y edges > and by 
(hewing them diftinctly frcm one brim thorough the Center to 
the other-, which the Sphericall Gaffe came farr fhorc of. And 
this effedtthe new-figur'd Gaffe periorm'd only on one of its 
fides, and not on the other, as being of a different figure from 
Sphericall-G'affes, which performe their ef&di near equally on 
both fides. 
Laftly, Thttwo Burning- Concaves ol this new-invented fi- 
gure were, the 00* of /?# inches Diameter, its focus three inches 
diitant from the Center thereof $ the other of the fame Diame- 
ter , but lefs concave, and Its focus 10. inches diftant. Thefe , 
when approached to a large Candle lighted, did fomtwhat war me 
the faces of thofe 5 that were 4 or 5 foot diftant at leaft, an i when 
Xo i held 
