Lecture 3 — Why the sea does not increase. Rejection of Plato's Tartarus.

It is quite natural that some people should have been puzzled by the old question why such a mass of water leaves no trace anywhere (for the sea does not increase though innumerable and vast rivers are flowing into it every day.)

But if one considers the matter the solution is easy. The same amount of water does not take as long to dry up when it is spread out as when it is gathered in a body, and indeed the difference is so great that in the one case it might persist the whole day long while in the other it might all disappear in a moment—as for instance if one were to spread out a cup of water over a large table. This is the case with the rivers: all the time they are flowing their water forms a compact mass, but when it arrives at a vast wide place it quickly and imperceptibly evaporates.

But the theory of the Phaedo about rivers and the sea is impossible. There it is said that the earth is pierced by intercommunicating channels and that the original head and source of all waters is what is called Tartarus—a mass of water about the centre, from which all waters, flowing and standing, are derived. This primary and original water is always surging to and fro, and so it causes the rivers to flow on this side of the earth's centre and on that; for it has no fixed seat but is always oscillating about the centre. Its motion up and down is what fills rivers. Many of these form lakes in various places (our sea is an instance of one of these), but all of them come round again in a circle to the original source of their flow, many at the same point, but some at a point opposite to that from which they issued; for instance, if they started from the other side of the earth's centre, they might return from this side of it. They descend only as far as the centre, for after that all motion is upwards. Water gets its tastes and colors from the kind of earth the rivers happened to flow through.

But on this theory rivers do not always flow in the same sense. For since they flow to the centre from which they issue forth they will not be flowing down any more than up, but in whatever direction the surging of Tartarus inclines to. But at this rate we shall get the proverbial rivers flowing upwards, which is impossible.

Again, where is the water that is generated and what goes up again as vapor to come from? For this must all of it simply be ignored, since the quantity of water is always the same and all the water that flows out from the original source flows back to it again.

This itself is not true, since all rivers are seen to end in the sea except where one flows into another. Not one of them ends in the earth, but even when one is swallowed up it comes to the surface again.

And those rivers are large which flow for a long distance through a lowying country, for by their situation and length they cut off the course of many others and swallow them up. This is why the Istrus and the Nile are the greatest of the rivers which flow into our sea. Indeed, so many rivers fall into them that there is disagreement as to the sources of them both.

All of which is plainly impossible on the theory, and the more so as it derives the sea from Tartarus.

Enough has been said to prove that this is the natural place of water and not of the sea, and to explain why sweet water is only found in rivers, while salt water is stationary, and to show that the sea is the end rather than the source of water, analogous to the residual matter of all food, and especially liquid food, in animal bodies.

154. Here the Philosopher raises another doubt, against the position that the sea is the terminal of rivers. About this he does three things.

First, he raises the doubt which he says is an old one (355b20): namely, why is it that, whereas rivers without number and of immense size enter the sea every day, it does not seem to grow and gives no evidence that such a vast amount of water is flowing into it?

155. second at **but if one considers the matter **(355b24), he solves the problem and says that, although it is not unfitting that some should be puzzled at this, yet, after careful consideration, it is not difficult to see the solution. Thus, if an amount of water is poured over a certain surface, and the same volume is poured out in different areas, then, if the size of the surface is not the same, the time required for the drying-up of the water poured out is not equal, but there will be a difference arising from the difference of surface on which the water is poured, so that sometimes the water remains and does not dry up for a whole day, while sometimes it dries up under one's very eyes. For example, if someone should pour a cup of water upon a large table, all the water would dry up at once; but if the same amount were poured into some small place, it would be preserved for a long time. This is what happens with rivers and the sea: for the total water coming from the rivers to the sea is spread out over an area of the greatest latitude, and is forthwith imperceptibly dried up by the continuous evaporation of water, concerning which we spoke above.

156. third at but the theory of the Phaedo* *about rivers and the sea (355b32), he excludes a certain false solution to this problem.

First, he gives the solution and says that what Plato says about the sea and rivers in his book entitled the Phaedo, cannot be true. For he says there that all rivers and the sea meet at a source under the earth, as though the earth were perforated by the sea and rivers. This source, which according to him, is the source of all waters, is called "Tartarus," a certain vast body of water existing about the center of the world: from it, he says, come all the waters that do not flow, such as the sea and ponds, and waters that do flow, such as springs and rivers.

He says further that Tartarus flows in every direction to each of the rheums, i.e., to each of the streams of water. This happens because that source of all waters is forever in motion, for it has no fixed place in which to rest but is forever in motion about the center, as though wandering to and fro. Thus, when it is surging upward, it produces the flowing out of rheums, i.e., the streaming of seas and rivers, not only toward that portion of the earth we inhabit; but from many other parts of the earth it pours out other bodies of still water, akin to the sea which exists among us. But all seas and rivers are brought back by a certain cycle to that source whence they emerged, but in various ways. For some return according to the same place whence they flowed out, by a kind of reflex movement; others return along a route contrary to the one along which they emerged, so that, for example, if they emerged from beneath, they would flow back from above. We should not so think of "above" and "beneath" as to think that something could be beneath with respect to the center in which the primal source of waters is postulated: for from the surface of the earth to the center, there is a descent; but further, if the water should proceed beyond in a straight line, the course would be upward—movement from the center being the same as movement upward. And according to this it is easy to assign a cause for the various colors and tastes of water: because the flowing water acquires its color and taste from the type of earth through which it flows out.

157. second at but on this theory rivers do not always flow (356a14), he disposes of the aforesaid position with five reasons.

The first is that, since sometimes the rivers return by the same route and sometimes by a contrary one, it follows, according to this position, that the flow of rivers is not consistently in the same direction. For since they return to the center from which they flowed, they will not flow "below" any more than "above," if you compare the surface of the earth to the center, as is always understood. But in relation to the surface of the earth something is "up," and something "down," depending on height and depth. If the movement of rivers is caused from Tartarus' overflow and this overflow is in every direction, it follows that the water, impelled, as it were, by Tartarus, flows indiscriminately in every direction, just as Tartarus in its fluctuation goes in every direction. Consequently, what is said in the proverb will come to pass, namely, an up of rivers, i.e., rivers that are higher than the springs or that flow uphill—which is impossible.

He presents the second reason at again, where is the water that is generated (356a19), namely, that, according to the aforesaid position, it is seen that it would be necessary that an equal amount of water be always preserved—for he posits that as much water as flows from Tartarus returns to the source. Consequently, one must entirely exclude generation of water in the air and elevation of water from the earth by vaporizing—which is plainly false.

He presents the third reason at this itself is not true, since all rivers are seen to end (356a22), namely, that all rivers end at the sea which do not terminate at other rivers, and no river so ends in the earth as though perforating the earth and going to Tartarus. Indeed, if there are any rivers entering into the concavity of the earth, they emerge again at some other spot. Consequently, it is not seen to be true that rivers return to Tartarus.

The fourth reason which he presents at and those rivers are large (356a25) is this: if the course of rivers is caused by what flows out of Tartarus, it would be necessary that rivers have a vast abundance of water from the very start. But this we do not observe: among rivers, those are found to be large which flow a long course, since they receive the flowings of many rivers and cut off their route both as to place, because they are deeper and more concave, and as to length, because they follow a longer course. This is why the Ister, i.e., the Danube, and the Nile are the largest rivers flowing into the Mediterranean Sea, and concerning their sources different ones say different things, because of the variety of rivers that enter them.

He presents the fifth reason at all of which is plainly impossible (356a31), namely, that over and above the unacceptable aspects already indicated, there is also the fact that it would follow that the sea has its source from Tartarus. And this is not fitting, because, as has been said, the sea is seen to be the natural place of water.

158. third at enough has been said to prove (356a33), he brings together what has been said above. And he says that so much has been said about the fact that the place which the sea occupies is the natural place of water and not just the natural place of the sea, i.e., of salt water. And it has been stated why what is drinkable and sweet does not show up in the sea but does in flowing water: what is salty subsides in the sea, being, as it were, the residue from the evaporation of what is drinkable and sweet. Furthermore, it has been said that the sea is rather the end than the source of waters: since, namely, water is generated outside the sea, both in the air above (as was said of the generation of rain), and within the earth (as was said of the generation of springs and rivers); nevertheless, no matter where it is generated, water flows to the sea, unless it is prevented. And thus, salt water is akin to the residue of food in the bodies of animals: for the residue of food is salty and bitter. This is true of the residue of any food, but especially of moist food, as in the case of urine, which is more undigested and therefore more bitter and salty, as is evident.