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 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 or that determinate measure, I say it must be meant of the tangible, and not the visible extension, which, though immediately perceived, is nevertheless little taken notice of.