The judicious Dr. Smith, in his excellent system of
optics, maintains the contrary opinion, and offers some
reasonings and facts in proof of it He agrees with
Bishop Berkeley in attributing it entirely to custom,
that we see objects single with two eyes, as well as that



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268 THE PHILOSOPHY OP REtD. CCh. Vt

we see objects erect by inverted images. Having con-
sidered Bishop Berkeley's reasonings in the nth section,
we shall now beg leave to make some remarks on what
Dr. Smith hath said upon this subject, with the respect
due to an author to whom the world owes, not only many
valuable discoveries of his own, but those of the brightest
mathematical genius of this age, which, with great labour,
he generously redeemed from oblivion.
He observes, that the question, Why we see objects
single with two eyes ? is of the same sort with this, Why
we hear sounds single with two ears ? — and that the
same answer must serve both. The inference intended
to be drawn from this observation is, that, as the second
of these phenomena is the effect of custom, so likewise
is the first

Now, I humbly conceive that the questions are not so
much of the same sort, that the same answer must serve
for both; and, moreover, that our hearing single with
two ears, is not the effect of custom.
