Page:Philosophical Transactions - Volume 003.djvu/45

 Eye, it cannot be doubted, but that this deficiency of Vision is upon the optick Nerve.

This Discovery I communicated to many of my friends, who found the same thing, though not always just at the same distances; which diversity I adscribed to the different situation of the Optick Nerve.You have made it your self, in his Majesties Library, where I shewed it to those of your Illustrious Assmembly; and you as well as I, found the like variety, there being some, who, at the distances mention'd, lost the sight of a Paper, 8 inch, large, and others, who ceased not to see it, but when it was somewhat less, which appears not how it can be caused but by the differing magnitudes of the Optick Nerve in different Eyes.

This Experiment hath given me cause to doubt, Whether Vision was indeed perform'd in the Retina (as is the Common opinion) or rather in that other Membrane, which at the bottom of the Eye is seen through the Retina, and is called the Choroides. For if Vision were made in the Retina, it seems that then it should be made whereever the Retina is; and since the same covers the whole Nerve, as well as the rest of the bottom of the Eye, there appears no reason to me, why there should be no Vision in the place of the Optick Nerve where it is: on the contrary, if it be in the Choroides that Vision is made, it seems evident, that the reason, why there is none on the Optick Nerve, is, because that that Membrane (the Choroides) parts from the Edges of the said Nerve, and covers not the middle thereof, as it does the rest of the bottom of the Eye.

Upon this, I desire, you would give me your thoughts with freedom, since I am none of those that love to obtrude Conjectures for Demonstrations.

Very one wonders, that no person before you hath been aware of this Privation of Sight, which every one now finds, after you have given notice of it. But as to the Sequele, you draw from this Discovery, I see it not cogent, to abandon the Plea of the Retina for being the principal Organ of Vision, For (not to insist here on other considerations) it will be sufficient, now to take notice, that at the place of the Optick Nerve there is Rh