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On The Heavens   


place.

We have now outlined the views held as to the shape, position, and

rest or movement of the earth.



14



Let us first decide the question whether the earth moves or is at

rest. For, as we said, there are some who make it one of the stars,

and others who, setting it at the centre, suppose it to be 'rolled'

and in motion about the pole as axis. That both views are untenable

will be clear if we take as our starting-point the fact that the

earth's motion, whether the earth be at the centre or away from it,

must needs be a constrained motion. It cannot be the movement of the

earth itself. If it were, any portion of it would have this

movement; but in fact every part moves in a straight line to the

centre. Being, then, constrained and unnatural, the movement could not

be eternal. But the order of the universe is eternal. Again,

everything that moves with the circular movement, except the first

sphere, is observed to be passed, and to move with more than one

motion. The earth, then, also, whether it move about the centre or

as stationary at it, must necessarily move with two motions. But if

this were so, there would have to be passings and turnings of the

fixed stars. Yet no such thing is observed. The same stars always rise

and set in the same parts of the earth.

Further, the natural movement of the earth, part and whole alike, is

the centre of the whole-whence the fact that it is now actually

situated at the centre-but it might be questioned since both centres

are the same, which centre it is that portions of earth and other

heavy things move to. Is this their goal because it is the centre of

the earth or because it is the centre of the whole? The goal,

surely, must be the centre of the whole. For fire and other light

things move to the extremity of the area which contains the centre. It

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