He would not consider the ideas
of sight with reference to, or as having any connexion with, the ideas of
touch: his view of them being entirely terminated within themselves, he
can no otherwise judge them great or small than as they contain a greater
or lesser number of visible points. Now, it being certain that any
visible point can cover or exclude from view only one other visible
point, it follows that whatever object intercepts the view of another
hath an equal number of visible points with it; and consequently they
shall both be thought by him to have the same magnitude. Hence it is
evident one in those circumstances would judge his thumb, with which he
might hide a tower or hinder its being seen, equal to that tower, or his
hand, the interposition whereof might conceal experimental means the
firmament from his view, equal to the firmament: how great an inequality
soever there may in our apprehensions seem to be betwixt those two
things, because of the customary and close connexion that has grown up in
our minds between the objects of sight and touch; whereby the very
different and distinct ideas of those two senses are so blended and
confounded together as to be mistaken for one and the same thing; out of
which prejudice we cannot easily extricate ourselves.
80. For the better explaining the nature of vision, and setting the
manner wherein we perceive magnitudes in a due light, I shall proceed to
make some observations concerning matters relating thereto, whereof the
want of reflexion, and duly separating between tangible and visible
ideas, is apt to create in us mistaken and confused notions.
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