s, and thereby produce in our minds the
sensation of pleasure or pain. Now bodies operating on our organs, by an
immediate application, and the hurt or advantage arising therefrom,
depending altogether on the tangible, and not at all on the visible,
qualities of any object: this is a plain reason why those should be
regarded by us much more than these: and for this end the visive sense
seems to have been bestowed on animals, to wit, that by the perception of
visible ideas (which in themselves are not capable of affecting or any
wise altering the frame of their bodies) they may be able to foresee
(from the experience they have had what tangible ideas are connected with
such and such visible ideas) and damage or benefit which is like to
ensue, upon the application of their own bodies to this or that body
which is at a distance. Which foresight, how necessary it is to the
preservation of an animal, everyone's experience can inform him. Hence it
is that when we look at an object, the tangible figure and extension
thereof are principally attended to; whilst there is small heed taken of
the visible figure and magnitude, which, though more immediately
perceived, do less concern us, and are not fitted to produce any
alteration in our bodies.

60. That the matter of fact is true will be evident to anyone who
considers that a man placed at ten foot distance is thought as great as
if he were placed at a distance only of five foot: which is true not with
relation to the visible, but tangible greatness of the object: the
visible magnitude being far greater at one station: than it is at the
other.

61. Inches, feet, etc., are settled stated lengths whereby we measure
objects and estimate their magnitude: we say, for example, an object
appears to be six inches or six foot long. Now, that this cannot be meant
of visible inches, etc., is evident, because a visible inch is itself no
constant, determinate magnitude, and cannot therefore serve to mark out
and determine the magnitude of any other thing. Take an inch marked upon
a ruler: view it, successively, at the distance of half a foot, a foot, a
foot and a half, etc., from the eye: at each of which, and at all the
intermediate distances, the inch shall have a different visible
extension, i.e. there shall be more or fewer points discerned in it. Now
I ask which of all these various extensions is that stated, determinate
one that is agreed on for a common measure of other magnitudes? No