[ tyr ] 
DEMONSTRATION of NEWTON’s THEOREM for 
th CORRECTION of SPHERICAL ERRORS um 
the OBJECT GLASSES of TELESCOPES. By the Reve. 
MATTHEW YOUNG, D.D. S.F.T.C.D. and M.R.LA. 
Sir Ifaac Newton, in his Optics, B. I. Part I. p. 68, had ob- 
ferved, that were it not for the different refrangibility of the 
rays of light, telefcopes might. be brought to a great degree 
of perfection, by compofing the object glafs of two glaffes 
with water between them, in the following manner: 
ABC 
sy Hi 
DEF 
Let AD FC reprefent the object glafs compofed of two glafles 
ABED, and BEF alike convex on the outiides 4GD and 
CHF, and alike concave on the infides BME, BNE, with water 
i: in: 
Read Dec. 35 
1791. 
