But though the image on my retina of a child I see at ten feet from me is equal to the image I have of a giant thrity feet away, I yet see the giant three times larger than the child, because there occurs in my eye something that I can use to discover the difference in their distance, such as the image of intervening bodies between me and these two people, or the different disposition of my eyes when I fix them on each of them to see them distinctly, or one of the other means that can serve to disclose the distance of objects, of which I have spoken in the ninth chapter of the first book.