An Essay Towards a New Theory of Vision | Page 6

therefore a
manifest consequence from what bath been demonstrated, that instead
of the greater or lesser divergency of the rays, the mind makes use of
the greater or lesser confusedness of the appearance, thereby to
determine the apparent place of an OBJECT.
23 Nor doth it avail to say there is not any necessary connection
between confused VISION and distance, great or small. For I ask any
man what necessary connection he sees between the redness of a blush
and shame? And yet no sooner shall he behold that colour to arise in
the face of another, but it brings into his and the IDEA of that passion
which hath been observed to accompany it.
24. What seems to have misled the writers of optics in this matter is
that they imagine men judge of distance as they do of a conclusion in
mathematics, betwixt which and the premises it is indeed absolutely
requisite there be an apparent, necessary connection: but it is far
otherwise in the sudden judgments men make of distance. We are not
to think that brutes and children, or even grown reasonable men,
whenever they perceive an OBJECT to approach, or depart from them,
do it by virtue of GEOMETRY and DEMONSTRATION.
25. That one IDEA may suggest another to the mind it will suffice that
they have been observed to go together, without any demonstration of
the necessity of their coexistence, or without so much as knowing what
it is that makes them so to coexist. Of this there are innumerable
instances of which no one can be ignorant.
26. Thus, greater confusion having been constantly attended with
nearer distance, no sooner is the former IDEA perceived, but it suggests
the latter to our thoughts. And if it had been the ordinary course of
Nature that the farther off an OBJECT were placed, the more confused
it should appear, it is certain the very same perception that now makes

us think an OBJECT approaches would then have made us to imagine it
went farther off. That perception, abstracting from CUSTOM and
EXPERIENCE, being equally fitted to produce the IDEA of great
distance, or small distance, or no distance at all.
27. Thirdly, an OBJECT being placed at the distance above specified,
and brought nearer to the eye, we may nevertheless prevent, at least for
some time, the appearances growing more confused, by straining the
eye. In which case that sensation supplies the place of confused
VISION in aiding the mind to judge of the distance of the OBJECT; it
being esteemed so much the nearer by how much the effort or straining
of the eye in order to distinct VISION is greater.
28. I have here set down those sensations or IDEAS that seem to be the
constant and general occasions of introducing into the mind the
different IDEAS of near distance. It is true in most cases that divers
other circumstances contribute to frame our IDEA of distance, to wit,
the particular number, size, kind, etc., of the things seen. Concerning
which, as well as all other the forementioned occasions which suggest
distance, I shall only observe they have none of them, in their own
nature, any relation or connection with it: nor is it possible they should
ever signify the various degrees thereof, otherwise than as by
EXPERIENCE they have been found to be connected with them.
29. I shall proceed upon these principles to account for a phenomenon
which has hitherto strangely puzzled the writers of optics, and is so far
from being accounted for by any of their THEORIES OF VISION that
it is, by their own confession, plainly repugnant to them; and of
consequence, if nothing else could be objected, were alone sufficient to
bring their credit in question. The whole difficulty I shall lay before
you in the words of the learned Dr. Barrow, with which he concludes
his optic lectures:--
'I have here delivered what my thoughts have suggested to me
concerning that part of optics which is more properly mathematical. As
for the other parts of that science (which being rather physical, do
consequently abound with plausible conjectures instead of certain
principles), there has in them scarce anything occurred to my
observation different from what has been already said by Kepler,
Scheinerus, Descartes, and others. And methinks, I had better say
nothing at all, than repeat that which has been so often said by others. I

think it therefore high time to take my leave of this subject: but before I
quit it for good and all, the fair and ingenuous dealing that I owe both
to you and to truth obligeth me to acquaint you with a certain untoward
difficulty, which seems directly opposite to the doctrine I have been
hitherto inculcating, at least, admits of no solution