4. But if any perhaps attend to what I am about to mention, they will find no such trouble in this inquiry. Commonly, when we have looked for some little time at a light, and then shut our eyes, there seem to play before our eyes certain bright colors variously changing themselves, and shining less and less until they wholly cease; and these we must understand to be the remains of that form which was wrought in the sense, while the shining body was seen, and that these variations take place in them as they slowly and step by step fade away. For the lattices, too, of windows, should we happen to be gazing at them, appear often in these colors; so that it is evident that our sense is affected by such impressions from that thing which is seen. That form therefore existed also while we were seeing, and at that time it was more clear and express. But it was then closely joined with the species of that thing which was being perceived, so that it could not be at all distinguished from it; and this was vision itself. Why, even when the little flame of a lamp is in some way, as it were, doubled by the divergent rays of the eyes, a twofold vision comes to pass, although the thing which is seen is one. For the same rays, as they shoot forth each from its own eye, are affected severally, in that they are not allowed to meet evenly and conjointly, in regarding that corporeal thing, so that one combined view might be formed from both. And so, if we shut one eye, we shall not see two flames, but one as it really is. But why, if we shut the left eye, that appearance ceases to be seen, which was on the right; and if, in turn, we shut the right eye, that drops out of existence which was on the left, is a matter both tedious in itself, and not necessary at all to our present subject to inquire and discuss. For it is enough for the business in hand to consider, that unless some image, precisely like the thing we perceive, were produced in our sense, the appearance of the flame would not be doubled according to the number of the eyes; since a certain way of perceiving has been employed, which could separate the union of rays. Certainly nothing that is really single can be seen as if it were double by one eye, draw it down, or press, or distort it as you please, if the other is shut.