That each of these Pearls or _Hemispheres_ is a perfect eye, I think we
need not doubt, if we consider onely the outside or figure of any one of
them, for they being each of them cover'd with a transparent protuberant
_Cornea_, and containing a liquor within them, resembling the watry or
glassie humours of the eye, must necessarily refract all the parallel Rays
that fall on them out of the air, into a point not farr distant within
them, where (in all probability) the _Retina_ of the eye is placed, and
that opacous, dark, and mucous inward coat that (I formerly shew'd) I found
to subtend the concave part of the cluster is very likely to be that
_tunicle_ or coat, it appearing through the _Microscope_ to be plac'd a
little more than a Diameter of those Pearls below or within the _tunica
cornea_. And if so, then is there in all probability, a little Picture or
Image of the objects without, painted or made at the bottom of the _Retina_
against every one of those Pearls, so that there are as many impressions on
the _Retina_ or opacous skin, as there are Pearls or _Hemispheres_ on the
cluster. But because it is impossible for any protuberant surface
whatsoever, whether _sphaerial_ or other, so to refract the Rays that come
from farr remote _lateral_ points of any Object as to collect them again,
and unite them each in a distinct point, and that onely those Rays which
come from some point that lies in the _Axis_ of the Figure produc'd, are so
accurately refracted to one and the same point again, and that the
_lateral_ Rays, the further they are remov'd, the more imperfect is their
refracted confluence; It follows therefore, that onely the Picture of those
parts of the external objects that lie in, or neer, the _Axis_ of each
_Hemisphere_, are discernably painted or made on the _Retina_ of each
_Hemisphere_, and that therefore each of them can distinctly sensate or see
onely those parts which are very neer perpendicularly oppos'd to it, or lie
in or neer its optick _Axis_.
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