^58 MifceUanea Curiofa, 



without, and the Species reprefented thereby 

 will be as big as the Life ; but if it were a 

 Flano~Convex 9 the fame diftanee will be =: %-p 

 or in Glafs to four times the Radiw of the 

 Convexity ; but of this Method I may enter- 

 tain the Curious at {bme other Time, and {hew 

 how to magnifie or diminifli an Ob]e6b in any 

 proportion ailign'd, (which yet will be obvious 

 enough from what is here deliver'd. as likewife how 

 to ereft the Object which in this Method is repre- 

 prefented inverted. 



A Second life is to find what Convexity or 

 Concavity is required, to make a vaftly di-* 

 ftant Objed be reprefented at a given Focus, 

 after the one Surface of the Lens is formed ; 

 which is but a Corollary of our Theorem for 

 finding ?, having /?, d, r and / given ; for d 



r f 



being infinite, that Rule becomes — - = ?, 



? r — f 



r f 



that is in Glafs — — - — ?, whence if f be 



% r — / 



greater than x r, § becomes Negative, and 



r f ■'■'■■M 



P* i s the Radius of the Concave (ought. 



f —* 1 r 



Thoie that are wholly to begin with this 

 Dioptrical Science, cannot do better than to 

 read with Attention a late Treatife of Diop* 

 tricks, publifhed by PV. Molineux^ Efcj, R. S. S. 

 who has at large {hewn the Nature of Optick 

 Glafles, and the Conftru&ion and life of Mi- 

 crofcopes and Telefcopes ; and though (bme 

 nicely Critical have endeavour'd to fpy Fault?, 

 and to traduce the Book ; yet having long 

 fince examined it with Care, I affirm, that if 

 I can judge, it hath but two things that with 



any 



