[Sidenote: _How things happen to be seen as double._] As for Polyphemus, although the story be fabulous, the monstrosity is not impossible. For the act of Vision may be performed with one eye; and in the deception and fallacy of sight, hath this advantage of two, that it beholds not objects double, or sees two things for one. For this doth happen when the axis of the visive cones, diffused from the object, fall not upon the same plane; but that which is conveyed into one eye, is more depressed or elevated then that which enters the other. So if beholding a Candle, we protrude either upward or downward the pupill of one eye, the object will appear double; but if we shut the other eye, and behold it with one, it will their appear but single; and if we abduce the eye unto either corner, the object will not duplicate: for in that position the axis of the cones remain in the same plane, as is demonstrated in the opticks, and delivered by _Galen_, in his tenth _De usu partium_. Relations also there are of men that could make themselves invisible, which belongs not to this discourse: but may serve as notable expressions of wise and prudent men, who so contrive their affairs, that although their actions be manifest, their designs are not discoverable. In this acception there is nothing left of doubt, and _Giges_ Ring remaineth still amongst us: for vulgar eyes behold no more of wise men then doth the Sun: they may discover their exteriour and outward ways, but their interiour and inward pieces he only sees, that sees into their beings. CHAPTER XXI Of the Chameleon. Concerning the _Chameleon_ there generally passeth an opinion that it liveth only upon air, and is sustained by no other aliment: Thus much is in plain terms affirmed by _Solinus_, _Pliny_, and others, and by this periphrasis is the same described by _Ovid_. All which notwithstanding, upon enquiry I find the assertion mainly controvertible, and very much to fail in the three inducements of belief.