Page:Ferrier's Works Volume 3 "Philosophical Remains" (1883 ed.).djvu/353

Rh still it is never seen, it is merely suggested by the other object which alone is presented to the vision.

By looking through a pair of spectacles, any one may convince himself of the impossibility of our seeing the real and tangible magnitude of things, or of our seeing anything which exceeds the expansion of the retina. A lofty tower, you will say, exceeds the expansion of the retina, certainly a tangible, a suggested tower, does so: but does a visible, a seen tower, ever do so? Make the experiment, good reader, and you will find that it never does. Look, then, at this tower from a small distance, through a pair of spectacles, which form a sort of projected retina, not much, if at all, larger than your real retina. At first sight you will probably say that it looks about a hundred feet high, and, at any rate, that you see it to be infinitely larger than your own eye. But look again, attending in some degree to the size of your spectacle glasses, and you shall see that it does not stretch across one half, or perhaps one fourth, of their diameter. And if a fairy pencil, as Adam Smith supposes, were to come between your eye and the glass, the picture sketched by it thereon, answering in the exactest conformity to the dimensions of the tower you see, would be an image, probably not the third of an inch high, or the hundredth part of an inch broad. This is certainly not what you seem to see, but this is certainly what you do see. These are the dimensions into which your lofty tower has shrunk. Now is this tower, seen to be