based--namely, that contraries tend to rest at the greatest possible distance from one another, against which Bruno marshalled a whole army of facts. Away from the shadow of the earth there was perhaps no light but that of the sun, too strong for our eyes, for the daylight arose from a mixture of the light of the sun and the darkness of the earth; we could see other colours by it, for the reason that they were similarly composed--mixtures of light and darkness. The heat of the sun also was only bearable when tempered by the coolness of the earth or other planets. The body of the earth, great as it is, can bear this heat only through its swift revolution. As to the objection that if the earth moved we should feel its motion, Bruno remarked that when we are carried in a smoothly and continuously moving vehicle, not striking against any object, we do not perceive that we are moving, except by comparison with some object known to us to be fixed. Thus sense furnishes its own correction.[355] The differences in the distances of the planets from the sun, as seen from the earth, are explained much more readily by the assumption that they and the earth itself are moving about the sun, than by that of the centrality of the earth, which compelled astronomers to the complicated device of the epicycles.[356] The fact that the moon always turns the same face towards the earth disproved the Ptolemaic theory: were it on an epicycle, as was supposed, this would be impossible. According to the old doctrine, the earth was fixed immovably in the centre of the universe, while about it circled the spheres of sun, planets, and fixed stars. With Bruno, on the other hand, the centre of the universe is everywhere, or nowhere,--in other words it is relative to the body on which the spectator is supposed to stand.