* 4 OF, } eres eee ee 
Bae J 
divergence or convergence will produce no difference in the con- 
clufion of any confequence: See Emerfon’s Dioptrics, Cor. 7 & 8. 
Prop. 40. B. 3. And that perfect accuracy was not affected by 
Newton is evident from his words, “ will very much correct the 
‘¢ errors of refraction, fo far as they arife from the fphericalnefs 
“ of the figure.” 
We may obferve, from the expreffion laft deduced, that the 
ratio of the radii of the furfaces depends as well upon the 
refraGtion between air and glafs, as upon the refraCtion between 
glafs and water. We may alfo obferve, that in the laft term of 
the analogy, as it ftands in Newton’s text, we fhould read RR 
inftead of RK; which renders the whole confiftent, and re- 
moves a manifeft corruption, 
Ir the furfaces be not concentrical, each glafs becoming a 
menifcus, no error will thence arife ; becaufe the centre of the 
concave furface will be as much farther from the focus of 
the compound lens on one fide, as it is nearer to it on the 
other; and therefore the corre€tion by one furface will be as 
much too great, as too little by the other, fo that the fum of 
both aberrations will, in this cafe likewife, very nearly vanith, 
