The Figurative Motions of _Light_ and _Darkness_, are quite opposite; and the Figurative Motions of Colours, are as a Mean between both, being partly of the Nature of both: but, as the Figurative Motions of Light, in my opinion, are rare, straight, equal, even, smooth Figurative Motions: those of Darkness are uneven, ruff, or rugged, and more dense. Indeed, there is as much difference between Light and Darkness, as between Earth and Water; or rather, between Water and Fire; because each is an Enemy to other; and, being opposite, they endeavour to out-power each other. But this is to be noted, That Darkness is as visible to Human Perception, as Light; although the Nature of Darkness is, To obscure all other Objects besides it self: but, if Darkness could not be perceived, the Optick Perception could not know when it is dark; nay, particular dark Figurative Motions, are as visible in a general Light, as any other Object; which could not be, if Darkness was only a privation of Light, as the Opinions of many Learned Men are: but, as I said before, Darkness is of a quite different Figurative Motion, from Light; so different, that it is just opposite: for, as the property of Light is to divulge Objects; so, the property of Darkness is to obscure them: but, mistake me not; I mean, that Light and Darkness have such properties to our Perception: but, whether it is so to all Perceptions, is more than I know, or is, as I believe, known to any other Human Creature. CHAP. XXIX. Of COLOURS.