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 reason
can be assigned why we should pitch on one more than another: and except
there be some invariable, determinate extension fixed on to be marked to
the word inch, it is plain it can be used to little purpose; and to say a
thing contains this or that number of inches shall imply no more than
that it is extended, without bringing any particular idea of that
extension into the mind. Farther, an inch and a foot, from different
distances, shall both exhibit the same visible magnitude, and yet at the
same time you shall say that one seems several times greater than the
other. From all which it is manifest that the judgments we make of the
magnitude of objects by sight are altogether in reference to their
tangible extension. Whenever we say an object is great, or small, of this