Now, as we accurately distinguish the site or position of an Object by the
motion of the Muscles of the eye requisite to put the optick Line in a
direct position, and confusedly by the position of the imperfect Picture of
the object at the bottom of the eye; so are these _crustaceous_ creatures
able to judge confusedly of the position of objects by the Picture or
impression made at the bottom of the opposite Pearl, and distinctly by the
removal of the attentive or observing faculty, from one Pearl to another,
but what this faculty is, as it requires another place, so a much deeper
speculation. Now, because it were impossible, even with this multitude of
eye-balls, to see any object distinct (for as I hinted before, onely those
parts that lay in, or very neer, the optick Lines could be so) the
Infinitely wise Creator has not left the creature without a power of moving
the head a little in _Aerial crustaceous_ animals, and the very eyes also
in _crustaceous_ Sea-animals; so that by these means they are inabled to
direct some optick line or other against any object, and by that means they
have the visive faculty as compleat as any Animal that can move its eyes.
Distances of Objects also, 'tis very likely they distinguish, partly by the
consonant impressions made in some two convenient Pearls, one in each
cluster; for, according as those congruous impressions affect, two Pearls
neerer approach'd to each other, the neerer is the Object, and the farther
they are distant, the more distant is the Object: partly also by the
alteration of each Pearl, requisite to make the Sensation or Picture
perfect; for 'tis impossible that the Pictures of two Objects, variously
distant, can be perfectly painted, or made on the same _Retina_ or bottom
of the eye not altered, as will be very evident to any one that shall
attentively consider the nature of refraction.
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