Lecture 2 — The sea is shown to be the natural place of all water.

We must now discuss the origin of the sea, if it has an origin, and the cause of its salt and bitter taste.

What made earlier writers consider the sea to be the original and main body of water is this. It seems reasonable to suppose that to be the case on the analogy of the other elements. Each of them has a main bulk which by reason of its mass is the origin of that element, and any parts which change and mix with the other elements come from it. Thus the main body of fire is in the upper region; that of air occupies the place next inside the region of fire; while the mass of the earth is that round which the rest of the elements are seen to lie. So we must clearly look for something analogous in the case of water. But here we can find no such single mass, as in the case of the other elements, except the sea. River water is not a unity, nor is it stable, but is seen to be in a continuous process of becoming from day to day. It was this difficulty which made people regard the sea as the origin and source of moisture and of all water. And so we find it maintained that rivers not only flow into the sea but originate from it, the salt water becoming sweet by filtration.

But this view involves another difficulty. If this body of water is the origin and source of all water, why is it salt and not sweet?

The reason for this, besides answering this question, will ensure our having a right first conception of the nature of the sea. The earth is surrounded by water, just as that is by the sphere of air, and that again by the sphere called that of fire (which is the outermost both on the common view and on ours). Now the sun, moving as it does, sets up processes of change and becoming and decay, and by its agency the finest and sweetest water is every day carried up and is dissolved into vapor and rises to the upper region, where it is condensed again by the cold and so returns to the earth. This, as we have said before, is the regular course of nature.

Hence all my predecessors who supposed that the sun was nourished by moisture are absurdly mistaken. Some go on to say that the solstices are due to this, the reason being that the same places cannot always supply the sun with nourishment and that without it he must perish. For the fire we are familiar with lives as long as it is fed, and the only food for fire is moisture.

As if the moisture that is raised could reach the sun!

Or this ascent were really like that performed by flame as it comes into being, and to which they supposed the case of the sun to be analogous! Really there is no similarity. A flame is a process of becoming, involving a constant interchange of moist and dry. It cannot be said to be nourished since it scarcely persists as one and the same for a moment. This cannot be true of the sun; for if it were nourished like that, as they say it is, we should obviously not only have a new sun every day, as Heraclitus says, but a new sun every moment.

Again, when the sun causes the moisture to rise, this is like fire heating water. So, as the fire is not fed by the water above it, it is absurd to suppose that the sun feeds on that moisture, even if its heat made all the water in the world evaporate.

Again, it is absurd, considering the number and size of the stars, that these thinkers should consider the sun only and overlook the question how the rest of the heavenly bodies subsist.

Again, they are met by the same difficulty as those who say that at first the earth itself was moist and the world round the earth was warmed by the sun, and so air was generated and the whole firmament grew, and the air caused winds and solstices. The objection is that we always plainly see the water that has been carried up coming down again. Even if the same amount does not come back in a year or in a given country, yet in a certain period all that has been carried up is returned. This implies that the celestial bodies do not feed on it, and that we cannot distinguish between some air which preserves its character once it is generated and some other which is generated but becomes water again and so perishes; on the contrary, all the moisture alike is dissolved and all of it condensed back into water.

The drinkable, sweet water, then, is light and is all of it drawn up: the salt water is heavy and remains behind, but not in its natural place. For this is a question which has been sufficiently discussed (I mean about the natural place that water, like the other elements, must in reason have), and the answer is this. The place which we see the sea filling is not its natural place but that of water. It seems to belong to the sea because the weight of the salt water makes it remain there, while the sweet, drinkable water which is light is carried up. The same thing happens in animal bodies. Here, too, the food when it enters the body is sweet, yet the residuum and dregs of liquid food are found to be bitter and salt. This is because the sweet and drinkable part of it has been drawn away by the natural animal heat and has passed into the flesh and the other parts of the body according to their several natures. Now just as here it would be wrong for any one to refuse to call the belly the place of liquid food because that disappears from it soon, and to call it the place of the residuum because this is seen to remain, so in the case of our present subject. This place, we say, is the place of water. Hence all rivers and all the water that is generated flow into it: for water flows into the deepest place, and the deepest part of the earth is filled by the sea. Only all the light and sweet part of it is quickly carried off by the sun, while the rest remains for the reason we have explained.

147. Here he begins to search into the truth about the opinions which the ancient natural philosophers held about the sea.

First, he shows what his intention is about (354b1) and says that it is about the generation of the sea: if it was made, and of its savor—as to what is the cause of its salty and bitter taste.

second, he pursues the proposition, at what made earlier writers consider the sea to be the original and main body of water (354b2). This is divided into three parts:

In the first he determines about the nature of the sea: whether it is the natural place of water, at (354b2);

in the second about its generation: whether or not it was made, at we must now explain why the sea is salt (356b4);

in the third about its savor: why it is salty, at to return to the saltiness of the sea (357a5).

The first part is divided into two parts:

in the first he shows the opinion of the ancients about the nature of the sea (354b2);

in the second he objects against it, at but this view involves another difficulty (354b15).

148. He says therefore first (354b2) that the ancients thought the sea to be the source of all water, and that it is the substance and body of the totality of water, as though the sea were the natural place of water. And the cause which led them to this was that it seemed reasonable that, just as the main bulk of all other elements is gathered into one place, and there is one source from which are derived those portions of that element which mingle with other elements, due to the size of the elemental substance, so too with water. For we observe that the main body of fire exists in the upper region of this lower world, which is its natural place; likewise, the main body of air exists under the region of fire, as though gathered together in its appropriate place; and it is plain that the body of earth is in the center, around which all other bodies are ordered. Hence it is plain that according to the same reasoning, it is also necessary that there be a place where the main bulk of water be congregated, as in its proper and natural place. Such a place can be naught but the sea: because the waters of streams are not all of them together, whereas for one element there must be one continuous place. Further, the water of rivers is not stationary but flowing, whereas every element must be stable in its proper place—for the water of rivers flows so as to seem to be forever coming into existence and not remaining in the same place.

On account of this problem they thought that the sea was the source of all water and of all moist things. On which account they thought that all rivers not only flow into the sea, but from it as well—since the natural place of an element seems to be the source and terminus of the movements of all things that possess its nature, for all things naturally tend to their own place. And according to the ancients it was also the source since they held the elements to be ungenerated and incorruptible—hence water was not newly generated. Thus, wherever water might be found outside its proper place, it would have had to have flowed from the natural place of water.

And because one could object that the sea is salty, whereas the water of rivers is sweet, and consequently does not seem to flow from the sea, they add, to dismiss this objection, that when something salty is filtered, it becomes sweet; and so sea water, when filtered through earth, becomes drinkable in rivers.

149. Then when he says, but this view involves another difficulty (354b15) he raises certain doubts about these previous determinings:

first, a doubt against the sea's being the natural place of water (354b16);

second, against the sea's being the terminus of running waters, at it is quite natural that some people should have been puzzled by the old question (355b20).

About the first he does two things.

First, he raises this doubt (354b15), which is as follows: If the sea is the source of all water as though it were the natural place of water, why is sea water not sweet and drinkable but salty? For every element in its primal place is seen to be untransformed and in its natural state—while saltiness is not a natural property of water but is due to some transmutations.

150. second at the reason for this (354b16), he solves this doubt. In connection with this, he does three things:

first, from matters already determined he takes something necessary for the solution;

second, from what was proposed he dismisses a certain false opinion, at hence all my predecessors (354b32);

third, he settles the doubt, at **the drinkable, sweet water, then **(355a32).

He says therefore first (354b16), that in assigning the cause of this doubt, not only will it be solved, but it will be necessary through it to obtain the correct opinion about the sea. He recalls, therefore, that water is positioned around the earth, as the sphere of fire above the air, and as the sphere of air above the water. For fire is the highest of the elements, whether fire be taken as the heavenly body, as very many hold, or as a body situated under the heavenly body, as he held above. Now, since generation and corruption, and all changes affecting lower bodies, are caused by the movement of the sun, what is finest and sweetest in rarefied water must be, as evaporated continually, brought to an upper region, where it is again condensed by the power of the cold and carried downward to earth. And this is always happening by nature, as already stated.

151. Then when he says, hence all my predecessors (354b32), he uses this to dismiss a false opinion.

First, he cites the opinion and says that from the foregoing it is plain that those ancients should be laughed at who said that the sun was fed by the watery moisture, and that it moved about because the same place cannot always offer this nourishment which it must have or be destroyed by not having it. For they thought that the sun was of a fiery nature. Now it is plain that fire lasts only so long as it is fed, and that the moist alone is its food. Consequently, when the moisture is totally consumed, the fire dies out.

152. second at as if the moisture that is raised (355a5), he assails this opinion with five reasons.

The first is that vapor which is lifted upward does not ascend as far as the sun's place, so as to be its food. This is plain enough from what has been already said.

Then he presents the second reason at or this ascent (355a6), which is that those who held that opinion seemed to think that the rise of vapor to the sun is as the rise of smoke to a flame: from the latter they took their basis for thinking as they do about the sun. But there is no similarity. For a flame never remains the same individual but is continually becoming a new thing by the fact that other and other material is continually enkindled: the matter, originally moist and suitable for combustion, is completely dried up by the fire and ceases to be inflamed, and is then succeeded by other matter. And so it is plain that a flame is not fed, because what is fed must retain its identity, as is plain in animals and plants, whereas a flame persists as though for no time at all, as has been said. Now such a state of affairs cannot be true of the sun: for if it were fed in the way they claim, it would be re-born continually and not just once every day, as Heraclitus postulated.

He presents the third reason at again, when the sun causes the moisture to rise (355a15), and says that the rising of moist vapor to the sun is akin to the boiling of water in pans over a fire. But the fire burning under the pan is not fed by the evaporating water. Therefore, neither is the sun, if it should cause so much water to evaporate.

He presents the fourth reason at again, it is absurd (355a18), and says that it is inconsistent to postulate food for the sun only and not for the other stars, if they are to remain healthy, since they too are assumed by them to be of a fiery nature. Indeed, these stars are so many and so large that the totality of water would not be enough to feed them.

He presents the fifth reason at again, they are met by the same difficulty (355a21), and says that this argument is both against this position and against those who held that in the beginning the entire earth was covered with water, but that later, as the water was evaporated by the sun's heat, air was formed; and as a consequence, the whole heaven grew by the fact that air, being more rarefied, occupies more place than the water from which it is generated; what has been thus resolved out of water is the cause of winds and of the heaven's movement. Both, therefore, of these opinions are destroyed by the fact that we plainly see the return to earth, of whatever has been lifted upward from the water. And if it does not return to the same place and equally in all places (for in some regions there is more evaporation than rainfall), yet in various places, according to a certain order of time, all the matter that has been borne aloft returns again to earth. And so it is plainly not so that higher bodies are fed by vapors or that one portion of the vapors remains air and another returns to water.

153. Then when he says, the drinkable, sweet water, then (355a32), he concludes the solution of the aforesaid doubt, and says that since vapor is borne aloft, that which is sweet and drinkable is wholly carried up because of being lighter, whereas that which is salty, being heavier, remains below as in its proper place. For it seems to be reasonably and fittingly held in the difficulty previously set down that the sea is the natural place of water—for it is unreasonable that water should not have a proper natural place as do the other elements. But the solution of the difficulty raised against this from the saltiness of the sea is that the place occupied by the sea is the natural place of water qua water; whereas it seems to be the natural place of sea water only, because that which is salt remains below because of its heaviness, while the sweet is evaporated aloft, because of its lightness.

He gives an example based on what happens in the bodies of animals. Although the food taken in is sweet and moist, the residue that remains of the food, as well as the superfluous nutriment, appears bitter and salty, because the sweet element has been drawn to flesh and to every part of the body by natural heat, according as each several part is naturally apt to be nourished.

By analogy to this, he concludes that, just as it would be strange for a person to suppose that the belly is not the place of food but only of the residue, on the ground that when the members are being nourished, the matter of the food is forthwith removed from the belly and the residue remains, and such a person would not be judging wisely, because, as we have already said, it is the natural place of food qua food, and not just of the food present in the belly, so too at present, the place occupied by the sea is the natural place of water. Indeed, all water moves toward the sea as to its proper place; for the flow of water is toward what is more concave, as is the place of the sea. But although this is the natural place of water, yet what is sweet is forthwith borne aloft, because of the sun raising the vapor, while what is salty remains below for the reason already given.