by the eye in like
manner as thoughts by the ear.

51. No sooner do we hear the words of a familiar language pronounced in
our ears, but the ideas corresponding thereto present themselves to our
minds: in the very same instant the sound and the meaning enter the
understanding: so closely are they united that it is not in our power to
keep out the one, except we exclude the other also. We even act in all
respects as if we heard the very thoughts themselves. So likewise the
secondary objects, or those which are only suggested by sight, do often
more strongly affect us, and are more regarded than the proper objects of
that sense; along with which they enter into the mind, and with which
they have a far more strict connexion, than ideas have with words. Hence
it is we find it so difficult to discriminate between the immediate and
mediate objects of sight, and are so prone to attribute to the former
what belongs only to the latter. They are, as it were, most closely
twisted, blended, and incorporated together. And the prejudice is
confirmed and riveted in our thoughts by a long tract of time, by the use
of language, and want of reflexion. However, I believe anyone that shall
attentively consider what we have already said, and shall say, upon this
subject before we have done (especially if he pursue it in his own
thoughts) may be able to deliver himself from that prejudice. Sure I am
it is worth some attention, to whoever would understand the true nature
of vision.

52. I have now done with distance, and proceed to show how it is that we
perceive by sight the magnitude of objects. It is the opinion of some
that we do it by angles, or by angles in conjunction with distance: but
neither angles nor distance being perceivable by sight, and the things we
see being in truth at no distance from us, it follows that as we have
shown lines and angles not to be the medium the mind makes use of in
apprehending the apparent place, so neither are they the medium whereby
it apprehends the apparent magnitude of objects.

53. It is well known that the same extension at a near distance shall
subtend a greater angle, and at a farther distance a lesser angle. And by
this principle (we are told) the mind estimates the magnitude of an
object, comparing the angle under which it is seen with its distance, and
thence inferring the magnitude thereof. What inclines men to this mistake
(beside the humour of making one see by geometry) is that the same