Plato, Timaeus

[45a] to serve as instruments of transport, so that grasping with these and' supported thereon it was enabled to travel through all places, bearing aloft the chamber of our most divine and holy part. In this wise and for these reasons were legs and hands attached to all men; and inasmuch as they demand the forepart superior to the hinder part in honor and dignity, the Gods gave us the most part of our going in this direction. Thus it was necessary that man should have the forepart of his body distinct and dissimilar. Wherefore, dealing first with the vessel of the head, they set the face in the front thereof [45b] and bound within it organs for all the forethought of the Soul; and they ordained that this, which is the natural front, should be the leading part. And of the organs they constructed first light-bearing eyes, and these they fixed in the face for the reason following. They contrived that all such fire as had the property not of burning but of giving a mild light should form a body akin to the light of every day.¹ For they caused the pure fire within us, which is akin to that of day, to flow through the eyes in a smooth and dense stream; [45c] and they compressed the whole substance, and especially the center, of the eyes, so that they occluded all other fire that was coarser and allowed only this pure kind of fire to filter through. So whenever the stream of vision is surrounded by midday light, it flows out like unto like,² and coalescing therewith it forms one kindred substance along the path of the eyes' vision, wheresoever the fire which streams from within collides with an obstructing object without. And this substance, having all become similar in its properties because of its similar nature, [45d] distributes the motions of every object it touches, or whereby it is touched, throughout all the body even unto the Soul, and brings about that sensation which we now term “seeing.” But when the kindred fire vanishes into night, the inner fire is cut off; for when it issues forth into what is dissimilar it becomes altered in itself and is quenched, seeing that it is no longer of like nature with the adjoining air, since that air is devoid of fire. Wherefore it leaves off seeing, and becomes also an inducement to sleep. For the eyelids —whose structure the Gods devised [45e] as a safeguard for the vision,—when they are shut close, curb the power of the inner fire; which power dissipates and allays the inward motions, and upon their allaying quiet ensues; and when this quiet has become intense there falls upon us a sleep that is well-nigh dreamless; but when some greater motions are still left behind, according to their nature and the positions they occupy