10. With Chalcidius as Interpreter

To which the remaining members obey and follow as the dominant part, being rightly and deservedly subject to it, lest the head, lying humbly and without a fixed seat at the very bottom, should encounter the rough obstacles of earthy hollows—both inclines and declines—when it moved; especially since it was necessary for it to experience all kinds of motions. For this reason, therefore, it is supported by the vehicle of the body as if it were a citadel. There was also added around it the extendable and flexible substance of the arms, so that the use of grasping, releasing, proceeding, and resisting might be ready at will, while the divine burden of the head remains eminent. Furthermore, the divine mind, deeming the function of moving forward more convenient than retreating, willed that man should move forward rather than backward. Judging also the front parts of the body to be better than the rear, the Creator placed the mask of the countenance in man first of all, in the specific region of the head; he called this the face, and assigned to it instruments to assist the provident movements of the soul. From these, the first light-bearing orbs of the eyes shine forth, given for the following reason.

¶ There are, I believe, two powers of fire: one is devouring and destructive; the other is soothing with a harmless light. Therefore, the divine powers devised for the eyes a domestic and familiar body derived from that fire from which the light that brings the day is spread. For they willed that the internal fire of our body—being a sibling to the transparent, serene, and purified liquid fire—should flow and stream out through the eyes. Thus, through the smooth and densely packed orbs of light, which are curved as if with a firmer solidity, yet have a narrow and more subtle center, the serene fire flows out through that same middle point.

And so, when the daylight applies itself to the stream of vision, then surely these two similar things, encountering one another, cohere into the appearance of a single body; there the flashing rays of the eyes meet, and there the ray of the internal stream flowing out is struck back by the encounter with the adjacent image. Chalcidius is describing the "extramission" theory of vision, where the eye sends out light to meet the light of the world. Therefore, this whole, having obtained the same and similar experience, and because of the indifferent similarity of the effect of that experience, whenever it touches something else or is itself touched by another, spreads the motion of the touch through the whole body, extending through the body even to the soul, and effects the sense which is called sight.

But after the kindred fire has departed into the night, the vision, deserted by the help and fellowship of that light, is as if widowed. Since it proceeds into something dissimilar, it is changed and extinguished, having no natural communication with the nearby air, which lacks the splendor of fire; and it ceases to see, overcome by the allure of sleep. For the divine powers engineered the healthy covering of the eyelids for the eyes; when these are closed, that power of the internal fire is restrained by the blinking of the cover; being compressed, it spreads itself through the limbs, and as they are softened and relaxed, a healing rest grows strong.

¶ When this rest is more intense, whatever remains of the movements there are, and in whatever places those remains are, such and similar phantasms of dreams will be born; and memory will accompany those who have been awakened.

¶ But as for the images that arise in mirrors, and even the shadows seen on a wet surface, the explanation is easy to grasp. Since the meeting of both fires—the internal as well as the external—falls upon some smooth surface of matter, and being formed into many and various figures, the images bounce back from the sight of the polished body. Furthermore, the parts that are on the right appear on the left in these same mirrors, in an unusual manner; because the vision of the right parts is positioned against the left part of the mirror, and the left against the right, the image of the movement is gestured from the opposite side of the part from which the movement originates. ¶ But truly, the right parts of the body appear on the right, just as they are...