Translated by Stephen MacKenna and B. S. Page.
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2. The explanation by lesser angle of vision has been elsewhere dismissed; one point, however, we may urge here.
Those attributing the reduced appearance to the lesser angle occupied allow by their very theory that the unoccupied portion of the eye still sees something beyond or something quite apart from the object of vision, if only air-space.
Now consider some very large object of vision, that mountain for example. No part of the eye is unoccupied; the mountain adequately fills it so that it can take in nothing beyond, for the mountain as seen either corresponds exactly to the eye-space or stretches away out of range to right and to left. How does the explanation by lesser angle of vision hold good in this case, where the object still appears smaller, far, than it is and yet occupies the eye entire?
Or look up to the sky and no hesitation can remain. Of course we cannot take in the entire hemisphere at one glance; the eye directed to it could not cover so vast an expanse. But suppose the possibility: the entire eye, then, embraces the hemisphere entire; but the expanse of the heavens is far greater than it appears; how can its appearing far less than it is be explained by a lessening of the angle of vision?
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