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On The Heavens   



that the revolution of the larger circle should take the same time

as that of the smaller. And secondly, the fact that the heavens do not

break in pieces follows not only from this but also from the proof

already given of the continuity of the whole.

Again, since the stars are spherical, as our opponents assert and we

may consistently admit, inasmuch as we construct them out of the

spherical body, and since the spherical body has two movements

proper to itself, namely rolling and spinning, it follows that if

the stars have a movement of their own, it will be one of these. But

neither is observed. (1) Suppose them to spin. They would then stay

where they were, and not change their place, as, by observation and

general consent, they do. Further, one would expect them all to

exhibit the same movement: but the only star which appears to

possess this movement is the sun, at sunrise or sunset, and this

appearance is due not to the sun itself but to the distance from which

we observe it. The visual ray being excessively prolonged becomes weak

and wavering. The same reason probably accounts for the apparent

twinkling of the fixed stars and the absence of twinkling in the

planets. The planets are near, so that the visual ray reaches them

in its full vigour, but when it comes to the fixed stars it is

quivering because of the distance and its excessive extension; and its

tremor produces an appearance of movement in the star: for it makes no

difference whether movement is set up in the ray or in the object of

vision.

(2) On the other hand, it is also clear that the stars do not

roll. For rolling involves rotation: but the 'face', as it is

called, of the moon is always seen. Therefore, since any movement of

their own which the stars possessed would presumably be one proper

to themselves, and no such movement is observed in them, clearly

they have no movement of their own.

There is, further, the absurdity that nature has bestowed upon

them no organ appropriate to such movement. For nature leaves

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