Notwithstanding all this, I will readily own, that the judgment to be made of painting might become of universal certainty, or at least less alterable and precarious than almost any thing else. The reason is plain; there is a standard to go by that always remains the same. Painting is an imitation of nature, a copying of things which men have every where before them. My good humoured reader I hope will forgive me, if, thinking on this glorious invention, I make a reflection a little out of season, though very much conducive to my main design; which is, that valuable as the art is I speak of, we are beholden to an imperfection in the chief of our senses for all the pleasures and ravishing delight we receive from this happy deceit. I shall explain myself. Air and space are no objects of sight, but as soon as we can see with the least attention, we observe that the bulk of the things we see is lessened by degrees, as they are further remote from us, and nothing but experience, gained from these observations, can teach us to make any tolerable guesses at the distance of things. If one born blind should remain so till twenty, and then be suddenly blessed with sight, he would be strangely puzzled as to the difference of distances, and hardly able, immediately, by his eyes alone, to determine which was nearest to him, a post almost within the reach of his stick, or a steeple that should be half a mile off. Let us look as narrowly as we can upon a hole in a wall that has nothing but the open air behind it, and we shall not be able to see otherwise, but that the sky fills up the vacuity, and is as near us as the back part of the stones that circumscribe the space where they are wanting. This circumstance, not to call it a defect, in our sense of seeing, makes us liable to be imposed upon, and every thing, but motion, may, by art, be represented to us on a flat, in the same manner as we see them in life and nature. If a man had never seen this art put into practice, a looking-glass might soon convince him that such a thing was possible, and I cannot help thinking, but that the reflections from very smooth and well-polished bodies made upon our eyes, must have given the first handle to the inventions of drawings and painting.