ON THE MECHANISM OF THE EYE.

ascertaining, upon inspection, the exact focaldistance of every eye, and the remedy forits imperfections. Thirdly, to show the ac-curate adjustment of every part of the eye,for seeing with distinctness the greatest pos-sible extent of objects at the same instant.Fourthly, to measure the collective dispersionof coloured rays in the eye. Fifthly, byimmerging the eye in water, to demonstratethat its accommodation docs not depend onany change in the curvature of the cornea.Sixthly, by confining the eye at the extre-mities of its axis, to prove that no materialalteration of its length can take place. Se-venthly, to examine what inference can bedrawn from the experiments hitherto made

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on persons deprived of the lens ; to pursue theinquiry, on the principles suggested by Dr.Porterfield; and to confirm his opinion ofthe utter inability of such persons to changethe refractive state of the organ. Eighthly,to deduce, from the aberration of the lateralrays, a decisive argument in favour of achange in the figure of the crystalline; toascertain, from the quantity of this aberration,the form into which the lens appears to bethrown in my own eye, and the mode bywhich the change must be produced in thatof every other person. And I flatter myself,that I shall not be deemed too precipitate,in denominating this series of experimentssatisfactorily demonstrative.