[34] and these boundaries are evening and morning; the one of which heralds in the good tidings that the sun is about to rise, gently dissipating the darkness: and evening comes on as the sun sets, receiving gently the collective approach of darkness. And these, I mean morning and evening, must be placed in the class of incorporeal things, perceptible only by the intellect; for there is absolutely nothing in them which is perceptible by the external senses, but they are entirely ideas, and measures, and forms, and seals, incorporeal as far as regards the generation of other bodies.