GEOLOGY

The Rise of the Nile

Seneca, Natural Questions IV. 2.16–30.² Translation of John Clarke (London, 1910)

But I must now go on to inquire into the explanations of the occurrence of the rise of the Nile in summer;¹ and I will begin with the most ancient of them. Anaxagoras asserts that the snow melting on the peaks of Ethiopia is constantly running down to the Nile. All antiquity shared the same view, which is recorded by Aeschylus, Sophocles, and Euripides. But many proofs make it plain that it is a mistaken one. First of all, the blackened complexion of the people shows that Ethiopia is exceedingly hot. So do the habits of the Troglodytes (cave-dwellers), who for coolness have underground houses. The rocks glow with heat as if a fire had been applied, and that, not only at mid-day, but even toward nightfall. The dusty ground is so hot that no foot of man can endure it. Silver is un-soldered. The joints of statues are melted. No coating of plated metal will stick on. The south wind, too, coming from that tract of country, is the hottest of all winds. None of the animals that go to earth in winter ever hibernates there. Even in midwinter the serpent is seen above ground in the open. At Alexandria, too, which lies far north of this excessive heat, snow does not fall; but the upper regions have not even rain.

How then, I ask, could a district exposed to such broiling heat receive a snowfall sufficient to last through a whole summer? No doubt some of the mountains in Ethiopia, as welt as elsewhere, intercept snow; but there can never be a greater fall than in the Alps, or the peaks of Thrace, or the Caucasus. It is in spring, however, or early summer, that the rivers that flow from the European mountains are swollen; subsequently during winter time they decrease. The reason, of course, is that the rains in spring wash off so much of the snow, and the first heat of summer soon scatters the remnants. Neither the Rhine, nor the Rhone, nor the Danube, nor yet the Caystrus is liable to the catastrophe of an overflow in winter; their increase is in summer, though in those northern peaks where they rise the snow lies very deep. The Phasis, too, and the Dnieper would swell during summer if snows had the power of raising the rivers high in spite of the heat of that season. Besides, if this were the cause of the flooding of the Nile, its stream would be fullest in early summer; for that is the period when the snow is deepest and least impaired, and when from its softness the thaw is quickest. The Nile, however, has a regular increase to its stream during four months.¹

If one may believe Thales, the Etesian winds² hinder the descent of the Nile and check its course by driving the sea against its mouths. It is thus beaten back, and returns upon itself. Its rise is not the result of increase; it simply stops through being prevented from discharging, and presently, wherever it can, it bursts out into forbidden ground. Euthymenes of Marseilles.³ bears corroborative testimony: I have, he says, gone a voyage in the Atlantic Sea. It causes an increase in the Nile as long as the Etesian winds observe their season. For at that period the sea is cast up by pressure of the winds. When the winds have fallen, the sea is at rest, and supplies less energy to the Nile in its descent. Further, the taste of that sea is fresh, and its denizens resemble those of the Nile. Now, if the Etesian winds, as alleged, stir up the Nile, why, I should like to know, does its rise begin before them and last after them? Moreover, it does not rise higher in proportion to the violence of their blast. Nor does it swell and fall according as they blow furiously or gently. All which would happen if it derived from them the strength of its increase. Then, again, the Etesian winds beat on the shore of Egypt, and the Nile comes down in their teeth: whereas, if its rise is to be traced to them, the river ought to come from the same quarter as they do.⁴ Furthermore, if it flowed out of the sea, its waters would be clear and dark blue, not muddy, as they are. Add to this that Euthymenes’ evidence is refuted by a whole crowd of witnesses. At such a time when foreign parts were all unknown, there was opportunity for falsehood: people like Euthymenes had scope for giving currency to travellers’ myths. But nowadays the whole coast of the sea beyond Gibraltar is visited by trading vessels: none of the traders tell us that the Nile rises there, or that the sea in the Atlantic tastes differently from what it does elsewhere. The very nature of the sea forbids belief in the story that it is fresh: the freshest water is always lightest, and as such attracted by the sun in evaporation: the residuum, sea, must be salt. Besides, why, on this theory, does the Nile not rise in winter? The sea may be raised at that season by storms too, which are considerably greater than the Etesians; the latter are comparatively moderate in their force. Besides if the source were derived from the Atlantic Ocean, Egypt would be flooded all at once; but, as a matter of fact, the increase is very gradual.

Oenopides of Chios has another explanation: he says that in winter heat is stored up under the ground; that is why caves are then warm, and the water in wells is less cold. The veins of water are dried up by this internal heat, he thinks. In other countries rivers swell through rain: but the Nile, being aided by no rainfall, dwindles during the rainy season of winter, and by and by increases in summer, a season at which the interior of the earth is cold, and the frost returns to the springs. Now, if that were true, rivers in general would increase in summer, and all wells would then have greater abundance of water. Besides, it is not true that there is an increase in the heat underground in winter. Water and caves and wells are warm at that season because they do not admit the frosty air from without. Thus, they do not possess heat, they merely exclude cold. For the same reason they are chilly in summer, because the air heated by the sun is drawn off to a distance, and does not penetrate to them.

The next account is that of Diogenes of Apollonia.¹ It runs thus: The sun attracts moisture; the earth drained of it replenishes its supply in part from the sea, in part from other water. Now, it is impossible that one land should be dry and another overflowing with moisture. The whole earth is full of perforations, and there are paths of intercommunication from part to part. From time to time the dry parts draw upon the moist. Had not the earth some source of supply, it would ere this have been completely drained of its moisture. Well, then, the sun attracts the waves. The localities most affected are the southern. When the earth is parched, it draws to it more moisture. Just as in a lamp the oil flows to the point where it is consumed, so the water inclines toward the place to which the overpowering heat of the burning earth draws it. But where, it may be asked, is it drawn from? Of course, it must be from those northern regions of eternal winter, where there is a superabundance of it. This is why a swift current sets from the Black Sea toward the Lower Sea, without interruption, and not, as in the case of other seas, with alternate flow and ebb of tide; there is always a descending flood in the one direction. Unless this took place, and these routes supplied the means whereby what is lacking may be bestowed on each land, and what is superfluous may be given off, the whole earth would ere now have been either drained or flooded. Now, one would like to ask Diogenes, seeing the deep and all streams are in intercommunication, why the rivers are not everywhere larger in summer. Egypt, he will perhaps tell me, is more baked by the sun, and therefore the Nile rises higher from the extra supply it draws;

but in the other countries, too, the rivers receive some addition. Another question seeing that every land attracts moisture from other regions, and a greater supply in proportion to its heat, why is any part of the world without moisture? Another—why is the Nile fresh if its water comes from the sea? No river has a fresher and sweeter taste.

Cf. Aëtius IV. 1.4 (Diels, Fragmente der Vorsokratiker II⁵. 107)

[Democritus holds that] when the snow in the northern parts is melted at the time of the summer solstice and flows away, clouds are formed by the vapors. When the clouds are driven towards the south and towards Egypt by the etesian winds violent storms arise and cause the lakes and the Nile river to be filled.

Cf. Strabo XVII. 1.5

[Posidonius] says that Callisthenes, on the authority of Aristotle, holds that the summer rains are the cause of the overflow [of the Nile].

Cf. Proclus on Plato, Timaeus, vol. I, p. 121.8 (Diehl)

Eratosthenes declares it is no longer necessary to inquire as to the cause of the overflow of the Nile, since we know definitely that men have come to the sources of the Nile and have observed the rains there. This confirms Aristotle’s conclusion.¹

Cf. Lucretius VI. 712–737. Translation of Cyril Bailey

The Nile, the river of all Egypt, alone in the world rises, as summer comes, and overflows the plains. It waters Egypt often amid the hot season, either because in summer the north winds, which at that time are said to be the etesian winds, are dead against its mouths; blowing against its stream they check it, and driving the waters upwards fill the channel and make it stop. For without doubt these blasts, which are started from the chill constellations of the pole, are driven full against the stream. The river comes from the south out of the quarter where heat is born, rising among the black races of men of sunburnt colour far inland in the region of mid-day. It may be too that a great heaping up of sand may choke up the mouths as a bar against the opposing waves, when the sea, troubled by the winds, drives the sand within; and in this manner it comes to pass that the river has less free issue, and the waves likewise a less easy downward flow. It may be, too, perhaps that rains occur more at its source at that season, because the etesian blasts of the north winds then drive all the clouds together into those quarters. And, we may suppose, when they have come together driven towards the region of mid-day, there at last the clouds, thrust together upon the high mountains, are massed and violently pressed. Perchance it swells from deep among the high mountains of the Ethiopians, where the sun, traversing all with his melting rays, forces the white snows to run down into the plains.

¹ Few scientific questions were as widely discussed in antiquity as the cause of the annual rise of the Nile. The present discussion of Seneca, which ends so abruptly as to suggest that it was never completed or that there is a lacuna in the text, takes up some of the ancient theories. The true cause, in one sense, is the heavy seasonal rainfall in Ethiopia. [Edd.]

¹ The occurrence of maximum height at different times for different points along the course of the Nile is not mentioned by Seneca. [Edd.]

² The etesian or northerly winds blow with some regularity in the Mediterranean during the summer months. [Edd.]

³ How this navigator (who may have lived at the close of the sixth century B.C.) came to connect the Atlantic with the Nile is not known, if indeed the error is his. [Edd.]

⁴ Perhaps Seneca did not quite understand the argument, which held merely that the winds by blowing contrary to the direction of the river dam it up. [Edd.]

¹ Diogenes of Apollonia, a philosopher of the fifth century B.C., is important for his contribution to the biological theory of pneumatism. His description of the vascular system in man is preserved by Aristotle (History of Animals III. 2). [Edd.]

¹ See Aristotle, Frag. 246 (Rose).