Aristotle... justly reproves Democritus for saying, that if no medium were interposed, a pismire would be visible in the heavens; asserting, on the contrary, that if vacuity alone intervened, nothing possibly could be seen, because all vision is performed by changes or motions in the organ of sight; and all such changes or motions imply an interposed medium. Between the perceptions of the eye and of the ear there is a striking analogy. Bodies are only visible by their colour; and colour is only perceptible in light; and unless different motions were excited by light in the eye, colour and the distinctions of colour would no more be visible, than, independently of different vibrations communicated to the ear, sound, and the distinctions of sound, would be audible. When the vibrations in a given time are many, the sensation of sharpness or shrillness follows; when the vibrations are, in the same time, comparatively few, the sensation of flatness is the result: but the first sound does not excite many vibrations because it is shrill or sharp, but it is sharp because it excites many vibrations; and the second sound does not excite few vibrations because it is flat or grave, but it is grave because it excites few vibrations.
Aristotle