56.  Now in order to discover by what means the magnitude of tangible objects is perceived by sight.  I need only reflect on what passes in my own mind, and observe what those things be which introduce the ideas of greater or lesser into my thoughts, when I look on any object.  And these I find to be, first, the magnitude or extension of the visible object, which being immediately perceived by sight, is connected with that other which is tangible and placed at a distance.  Secondly, the confusion or distinctness.  And thirdly, the vigorousness or faintness of the aforesaid visible appearance.  Ceteris PARIBUS, by how much the greater or lesser the visible object is, by so much the greater or lesser do I conclude the tangible object to be.  But, be the idea immediately perceived by sight never so large, yet if it be withal confused, I judge the magnitude of the thing to be but small.  If it be distinct and clear, I judge it greater.  And if it be faint, I apprehend it to be yet greater.  What is here meant by confusion and faintness hath been explained in sect. 35.

57.  Moreover the judgments we make of greatness do, in like manner as those of distance, depend on the disposition of the eye, also on the figure, number, and situation of objects and other circumstances that have been observed to attend great or small tangible magnitudes.  Thus, for instance, the very same quantity of visible extension, which in the figure of a tower doth suggest the idea of great magnitude, shall in the figure of a man suggest the idea of much smaller magnitude.  That this is owing to the experience we have had of the usual bigness of a tower and a man no one, I suppose, need be told.

58.  It is also evident that confusion or faintness have no more a necessary connexion with little or great magnitude than they have with little or great distance.  As they suggest the latter, so they suggest the former to our minds.  And by consequence, if it were not for experience, we should no more judge a faint or confused appearance to be connected with great or little magnitude, than we should that it was connected with great or little distance.

59.  Nor will it be found that great or small visible magnitude hath any necessary relation to great or small tangible magnitude:  so that the one may certainly be inferred from the other.  But before we come to the proof of this, it is fit we consider the difference there is betwixt the extension and figure which is the proper object of touch, and that other which is termed visible; and how the former is principally, though not immediately taken notice of, when we look at any object.  This has been before mentioned, but we shall here inquire into the cause thereof.  We regard the objects that environ us in proportion as they are adapted to benefit or injure our own bodies, and thereby produce in our minds the sensation of pleasure or pain.  Now bodies operating on our organs, by an immediate application,