opinion of speculative men is that the two OPTIC AXES (the fancy that we
see only with one eye at once being exploded) concurring at the OBJECT do
there make an ANGLE, by means of which, according as it is greater or
lesser, the OBJECT is perceived to be nearer or farther off.

5. Betwixt which and the foregoing manner of estimating distance there is
this remarkable difference: that whereas there was no apparent, necessary
connection between small distance and a large and strong appearance, or
between great distance and a little and faint appearance, there appears a
very necessary connection between an obtuse angle and near distance, and
an acute angle and farther distance. It does not in the least depend upon
experience, but may be evidently known by anyone before he had
experienced it, that the nearer the concurrence of the OPTIC AXES, the
greater the ANGLE, and the remoter their concurrence is, the lesser will
be the ANGLE comprehended by them.

6. There is another way mentioned by optic writers, whereby they will
have us judge of those distances, in respect of which the breadth of the
PUPIL hath any sensible bigness: And that is the greater or lesser
divergency of the rays, which issuing from the visible point do fall on
the PUPIL, that point being judged nearest which is seen by most
diverging rays, and that remoter which is seen by less diverging rays:
and so on, the apparent distance still increasing, as the divergency of
the rays decreases, till at length it becomes infinite, when the rays
that fall on the PUPIL are to sense parallel. And after this manner it is
said we perceive distance when we look only with one eye.

7. In this case also it is plain we are not beholding to experience: it
being a certain, necessary truth that the nearer the direct rays falling
on the eye approach to a PARALLELISM, the farther off is the point of