Three Objects Discernible Only With Both Eyes
If you fix three pieces of paper against the wall of a room at equal
distances, at the height of your eye, placing yourself directly before
them, at a few yards' distance, and close your right eye, and look at
them with your left, you will see only two of them, suppose the first
and second; alter the position of your eye, and you will see the first
and third: alter your position a second time, you will see the second
and third, but never the whole three together; by which it appears,
that a person who has only one eye can never see three objects placed
in this position, nor all the parts of one object of the same extent,
without altering his situation.
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