Lecture 21 — Different opinions of the motion, rest, and shape of the earth

345 and the views advanced concerning its rest or motion are similar. For here too there is no general agreement. All who deny that the earth lies at the center think that it revolves about the center, and not the earth only but, as we said before, the 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.

346 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.

347 Indeed, as in any case the surface of the earth is not actually a center 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 center, 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 center by half the diameter of the earth.

348 Others, again, say that the earth, which lies at the center, is 'rolled', and thus in motion, about the axis of the whole heaven, So it stands written in the Timaeus.

349 There are similar disputes about the shape of the earth. Some think it is spherical, others that it is flat and drum-shaped.

350 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.

351 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.

352 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.

486. After presenting opinions about the position of the earth, the Philosopher here presents opinions about its motion and rest.

He presents two opinions;

the second of these is at others, again, say (293b30; [490]).

With respect to the first he does three things:

first he presents the theories;

secondly, he induces a certain proof thereof, at this, they say, accounts for the fact (293b23; [488]);

thirdly, he shows how they meet arguments brought against them, at indeed, as in any case the surface of the earth (293b25; [489]).

487. He says therefore first (293b16) that just as philosophers have spoken in various ways about the place of the earth, so also about its motion and rest. But those who say that it is not positioned in the middle of world, such as the Pythagoreans, assign to it a circular motion by which it is moved about the middle. Nor do they say that it is just this earth in which we live that is moved but also a certain other one which they called antichtona, i.e., in counter-opposition to this earth, as has been said above. This they posited on account of the perfection of the number 10, in order that, since there are 8 heavenly bodies circularly moved, namely, the sphere of the fixed stars and the 7 planets, the number of 10 might be fulfilled by positioning two earths circularly moved.

Now there are some Pythagoreans who claim that there are not only two earths circularly moved, but also several other bodies of earth in motion about the middle. These indeed are imperceptible to us because this earth on which we live is superimposed on the others, in such a way that the others follow its motion. Consequently, the interposition of this earth between out vision and those earths hides them from us.

488. Then, at this, they say, accounts for the fact (293b23) he presents their proof of what we have just stated. Now it is plain that just as an eclipse of the sun is due to the interposition of the moon between us and the sun, so the eclipse of the moon is due to the interposition of the earth between the sun and the moon. But the moon is eclipsed more often than the sun. This they said is due to the fact that there is but one solitary moon to eclipse the sun when interposited between us and it, but the moon is eclipsed not only by the earth on which we live but by several other earths.

But this argument of theirs is of no worth, because the moon is never found to be eclipsed except by the interposition of this earth between the moon and the sun, namely, when the moon enters the shadow of this earth. Eclipses of the moon occur more frequently than those of the sun, because a solar eclipse is very often impeded on account of the diversity of aspect.

489. Then, at indeed, as in any case the surface of the earth (293b25) he shows how they meet arguments leveled against them. The chief of these is that, unless the earth were in the middle of the world, the horizon which is a plane passing through our sight would not always cut the entire sphere and the greatest circles into two halves, in such a way, namely, that six signs [of the Zodiac] are always visible to us above the earth and six are under the earth. But their answer to this was that the whole earth is not a center, because a center is indivisible and a point, whereas the earth is a body possessing size. Hence, our circle which is on the surface of the earth is a full hemisphere's distance from the center—yet this does not prevent everything from appearing to us as though our eye were in the center. The reason for this is the smallness of the earth, which is as though nothing in size in comparison with the whole heaven. In like manner, they thought that if the earth on which we live is not in the middle, all things would appear to us as though the earth were in the middle of the universe, because even now the distance from the middle is not manifest as to appearance, although our sight is distant from the middle of the universe by half the earth. But this could be understood if the earth were a small distance from the middle but not if it were at a great distance therefrom. There are also certain other appearances which would not be saved if the earth were not in the middle—for example, what occurs in an eclipse of the moon, when there is direct opposition of the moon to the sun. For, unless the earth were always in the middle, an eclipse of the moon would not always occur when it is in opposition in the head or tail—yet our aspect counts for nothing in an eclipse of the moon.

490. Then, at others, again, say (293b30), he presents a second opinion. And he says that some, although they say that the earth is in the center, yet say it is moved and revolved about the never-shifting pole, i.e., about the axis of the world (for sometimes the heaven is called the "pole," sometimes the axis is, and sometime the ends of the axis, as when we speak of the arctic and antarctic pole). And this opinion, he says, is found in the Timaeus.

But it should be noted that Aristotle took what is here called "revolved" or "turned," from Plato's statement in the Timaeus: in Greek, "illomenum" about the pole in every way ordered. Now if illomenum is written in Greek with an iota, it means a "binding," but if written with a diphthong, it means "a hindrance." Now this word seems to be taken by Plato as it means a "binding," as is plain from what he says about the earth in the Phaedo, where he asserts it to be at rest in the middle and, as it were, held fast. Consequently, Aristotle seems to have taken the words of Plato in a way not intended by him.

Therefore, Alexander, excusing Aristotle, says that illomenum, properly signifies "preventing" or "compulsion," but because that meaning does not fit what Plato intends to say here Aristotle understood him as taking it in the extended sense of meaning, as transferred, "turning," which denotes motion. Nor does it make any difference in the present argument whether Plato has said elsewhere something that differed from what he had said, in the Phaedo, for some other reason. For Aristotle is here proposing what is written in Timaeus; whether it be introduced as an opinion accepted by Plato, or as the opinion of Timaeus, which he does not approve. That is why he does not say "as Plato says," but "as is written in the Timaeus."

But Simplicius has a barrage of objections against this.

First, because Timaeus there proves the earth is located and settled in the middle.

Secondly, because there the word illomenum is written with an iota, and thus signifies a "holding fast."

Thirdly, because a "turning" does not always imply motion—for circular figures are said to be "turned," i.e., facing [turned] in every direction, even if they are at rest.

Fourthly, because, since this word has many meanings, one should not have bent its meaning to a sense plainly contrary to Plato's intention.

But, against this, Simplicius again objects that it is not probable that Aristotle was ignorant either of the meaning of the word or of Plato's intention. Consequently, it can be said that, because it was possible for some to falsely interpret Plato's words, Aristotle removes the false understanding that could be obtained from these words, as he frequently does with passages from Plato. Or it can be said that the phrase, "and to be moved," is an interpolation by another. In the Greek there is stated illesthai, which is here translated, "to be revolved." Now what is written in the Greek can signify both a "holding fast" and "motion," so that we can understand that after Aristotle presented the Pythagorean theory of the motion of the earth about the middle, he here presents Plato's theory about the earth being at rest in the middle.

We can also say more briefly that one Heraclitus of Pontus posited the earth to be in motion in the center and the heaven to be at rest, and that it is his opinion that Aristotle is here introducing. The fact that he adds, "as stands written in the Timaeus," is to be referred, not to what was said, namely, "it is revolved and moved," but to what follows, namely, "that it is upon a fixed pole."

491. Then, at there are similar disputes about the shape (293b32) he gives the theories about the shape of the earth.

And first he presents the theories, and states that there are likewise problems about the shape of the earth, as there are about its motion and position. For some think that it is spherical, others that it is wide and having the shape of a tambourine.

492. Secondly, at for evidence they bring the fact that (294a1), he presents two reasons used to support this second theory.

The first of these (294a1) is that they make an argument of the fact that as the sun rises and sets, it is cut by the earth according to a straight, and not a circular, line—namely, when part of the sun appears above the earth, and part is hidden. Now if the earth were spherical, the line of section would seem to have to be circular, because two spherical bodies intersect with a circular intersection.

But he excludes this argument at in this they leave out of account (294a3), and says that those who present this argument do not consider the sun's distance from the earth and the greatness of the rotundity of each. For we sometimes see that even small circles, seem: from afar, appear after the manner of a straight line. There is all the more reason, therefore, for portions of large circles to appear straight from a distance, because they are less curved. However, this must be principally understood when the circle is in the same surface as our vision—for the intersection of the sun and moon, which is not in the same surface with our sight, is not seen as straight but as circular, as was said above when discussing the shape of the stars.

493. He gives a second argument at but they have another argument (294a8), and says that they add a further argument for the same, namely, that if the earth is to be at rest, it has to be flat. For a spherical shape is easy to move, because so little of it is in contact with a plane; but a wide shape is totally in contact with a plane, and is consequently apt for rest. And lest anyone believe that this explanation of the earth's rest is generally assigned by everyone, he adds that there are many different ways in which the motion and rest of the earth has been conceived, as will be plain from what will be said below.