178 OF SIGHT. 



exceed, according to Jurin, that of each, by more than 

 one thirteenth part. 



It is needless to add, what the celebrated painter, 

 Leonardo da Vinci, long since remarked, that in 

 viewing- distant objects, it is preferable to employ but 

 one eye.*(F) 



281. Sight can never occur unless the angle of vision 

 exceeds 34 seconds. This was proved by the very beau- 

 tiful experiments of the acute Tob. Mayer, who for- 

 merly was one of our number. And he demonstrated 

 the great excellence of the -human sight, by shewing 

 that this still remained the limit of vision under any 

 light, under the splendor of the meridian son and the 

 faint light of a lantern; so that vision remains almost 

 equally clear although the light be considerably di- 

 minished, f 



282. We may hence infer the prodigious minuteness 

 of the images of objects projected upon the retina, J 

 and nevertheless impressed so forcibly upon it, that, 

 under certain circumstances, their vestiges remain, after 

 the removal of the objects from before the eye. 



* Consult Lambert, sur la partic photometrique de Cart du pe'mtre in the 

 Mdm. dt FAcad. dcs Sciences tfe Berlin. 17(i8. p. 80 sq. 



f Tob. Mayer, Ea-perimenta circa visus aciem, in the Commentar. S&c. 

 Scient. Got tinge n. T. iv. 



J De la Hire, Accitlens de la vite. p. 3/5. 



Gasscndi, Vita Peireskii. p. 175sq. Hague. 1655. 4to. 



Franklin, Letters on Philosophical Subjects, at the end of his Expts. on Elec- 

 tricity. Lond. 1769. 4to. p. 469 sq. 



Rob. War. Darwin, Ea-perimenta nova de spcctrls s. imaginibus ocularib-its, 

 quce objectis litcidioribus antea visit, in oculo ciaiiso vel averno percipiitntur 1 . 

 Ltigd. Bat. 1785. 4to. 



Er. Darwin, Zoonnmia. T. i. 



C<. ITnuly, 13iblwtk.Ophthalmnlo!f.y.\, P. ii. p.i. 



