A Treatise on the Eye/Book 5/Chapter 2
CHAP. II.
Of the Erect Appearance of Objects.
Sect.
Pag.
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| 1. | The Pictures on the Retina are always inverted, yet Objects are always seen erect, | 229 |
| 2. | This Phænomenon shortly explained, | 229 |
CHAP. II.
Of the erect Appearance of Objects.
Sect. 1. IN explaining the Manner of Vision, and the Action of the Humours of the Eye, it was demonstrated, that the Images of visual Objects are painted on the Retina in an inverted Order; that is, the upper Part of the Object makes the lower Part of the Picture, and the Right-side of the Object makes, the Left-side of the Picture, and so of the other Parts. This gives occasion to the Question now before us, How we come to judge rightly of the erect Position of Objects, since their Pictures on the Retina are always inverted?
§ 2. To this I answer, That the Mind never sees any Picture painted on the Retina, and consequently never judges of the Object from what it observes in this Picture; for it has already been proved, that all our Sensations are present with the Mind and in the Sensorium; and that, in seeing any Object, the Mind, by virtue of a connate immutable Law, to which it has always been subjected, traces back its own Sensation from the Sensorium to the Retina, and from thence outwards, along Right-lines drawn perpendicularly from every Point of the Retina, on which any Impression is made by the Rays forming the Picture, towards the Object itself; by which Means the Mind or visive Faculty does always see every Point of the Object, not in the Sensorium or Retina, but without the Eye in these perpendicular Lines: But these perpendicular Lines do nearly coincide with the Axes of the several Pencils of Rays that flow to the Eye from the several Points of the Object, and since the Mind has also a Power of judging rightly of the Distance of Objects, it from thence follows, that every Point of the Object must appear, and be seen in the Place where it is; and consequently the Object itself must appear in its true erect Position, notwithstanding its Picture on the Retina is inverted. This I had occasion to say something of before; and therefore I need not enlarge further on it in this Place.