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On The Heavens   

counter-earth as well. Some of them even consider it possible that

there are several bodies so moving, which are invisible to us owing to

the interposition of the earth. This, they say, accounts for the

fact that eclipses of the moon are more frequent than eclipses of

the sun: for in addition to the earth each of these moving bodies

can obstruct it. Indeed, as in any case the surface of the earth is

not actually a centre but distant from it a full hemisphere, there

is no more difficulty, they think, in accounting for the observed

facts on their view that we do not dwell at the centre, than on the

common view that the earth is in the middle. Even as it is, there is

nothing in the observations to suggest that we are removed from the

centre by half the diameter of the earth. Others, again, say that

the earth, which lies at the centre, is 'rolled', and thus in

motion, about the axis of the whole heaven, So it stands written in

the Timaeus.

III. There are similar disputes about the shape of the earth. Some

think it is spherical, others that it is flat and drum-shaped. For

evidence they bring the fact that, as the sun rises and sets, the part

concealed by the earth shows a straight and not a curved edge, whereas

if the earth were spherical the line of section would have to be

circular. In this they leave out of account the great distance of

the sun from the earth and the great size of the circumference, which,

seen from a distance on these apparently small circles appears

straight. Such an appearance ought not to make them doubt the circular

shape of the earth. But they have another argument. They say that

because it is at rest, the earth must necessarily have this shape. For

there are many different ways in which the movement or rest of the

earth has been conceived.

The difficulty must have occurred to every one. It would indeed be a

complacent mind that felt no surprise that, while a little bit of

earth, let loose in mid-air moves and will not stay still, and more

there is of it the faster it moves, the whole earth, free in midair,

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