19. I know it is a received opinion that by altering the disposition of
the eyes the mind perceives whether the angle of the OPTIC AXES is made
greater or lesser. And that accordingly by a kind of NATURAL
GEOMETRY it judges the point of their intersection to be nearer
or farther off. But that this is not true I am convinced by my own
experience, since I am not conscious that I make any such use of the
perception I have by the turn of my eyes. And for me to make those
judgments, and draw those conclusions from it, without knowing that I do
so, seems altogether incomprehensible.

20. From all which it follows that the judgment we make of the distance
of an OBJECT, viewed with both eyes, is entirely the RESULT OF
EXPERIENCE. If we had not constantly found certain sensations arising
from the various disposition of the eyes, attended with certain degrees
of distance, we should never make those sudden judgments from them
concerning the distance of OBJECTS; no more than we would pretend to
judge a man's thoughts by his pronouncing words we had never heard
before.

21. Secondly, an OBJECT placed at a certain distance from the eye, to
which the breadth of the PUPIL bears a considerable proportion, being
made to approach, is seen more confusedly: and the nearer it is brought
the more confused appearance it makes. And this being found constantly to
be so, there ariseth in the mind an habitual CONNECTION between the
several degrees of confusion and distance; the greater confusion still
implying the lesser distance, and the lesser confusion the greater
distance of the OBJECT.

22. This confused appearance of the OBJECT doth therefore seem to be the