Herodotus: II 19-31. On the Nile River
Now the Nile, when it overflows, floods not only the Delta, but also the tracts of country on both sides the stream which are thought to belong to Libya and Arabia, in some places reaching to the extent of two days' journey from its banks, in some even exceeding that distance, but in others falling short of it.
Concerning the nature of the river, I was not able to gain any information either from the priests or from others. I was particularly anxious to learn from them why the Nile, at the commencement of the summer solstice, begins to rise, and continues to increase for a hundred days- and why, as soon as that number is past, it forthwith retires and contracts its stream, continuing low during the whole of the winter until the summer solstice comes round again. On none of these points could I obtain any explanation from the inhabitants, though I made every inquiry, wishing to know what was commonly reported- they could neither tell me what special virtue the Nile has which makes it so opposite in its nature to all other streams, nor why, unlike every other river, it gives forth no breezes from its surface.
Some of the Greeks, however, wishing to get a reputation for cleverness, have offered explanations of the phenomena of the river, for which they have accounted in three different ways. Two of these I do not think it worth while to speak of, further than simply to mention what they are. One pretends that the Etesian winds cause the rise of the river by preventing the Nile-water from running off into the sea. But in the first place it has often happened, when the Etesian winds did not blow, that the Nile has risen according to its usual wont; and further, if the Etesian winds produced the effect, the other rivers which flow in a direction opposite to those winds ought to present the same phenomena as the Nile, and the more so as they are all smaller streams, and have a weaker current. But these rivers, of which there are many both in Syria and Libya, are entirely unlike the Nile in this respect.
The second opinion is even more unscientific than the one just mentioned, and also, if I may so say, more marvellous. It is that the Nile acts so strangely, because it flows from the ocean, and that the ocean flows all round the earth.
The third explanation, which is very much more plausible than either of the others, is positively the furthest from the truth; for there is really nothing in what it says, any more than in the other theories. It is, that the inundation of the Nile is caused by the melting of snows. Now, as the Nile flows out of Libya, through Ethiopia, into Egypt, how is it possible that it can be formed of melted snow, running, as it does, from the hottest regions of the world into cooler countries? Many are the proofs whereby any one capable of reasoning on the subject may be convinced that it is most unlikely this should be the case. The first and strongest argument is furnished by the winds, which always blow hot from these regions. The second is that rain and frost are unknown there. Now whenever snow falls, it must of necessity rain within five days;.so that, if there were snow, there must be rain also in those parts. Thirdly, it is certain that the natives of the country are black with the heat, that the kites and the swallows remain there the whole year, and that the cranes, when they fly from the rigours of a Scythian winter, flock thither to pass the cold season. If then, in the country whence the Nile has its source, or in that through which it flows, there fell ever so little snow, it is absolutely impossible that any of these circumstances could take place.
As for the writer who attributes the phenomenon to the ocean, his account is involved in such obscurity that it is impossible to disprove it by argument. For my part I know of no river called Ocean, and I think that Homer, or one of the earlier poets, invented the name, and introduced it into his poetry.
Perhaps, after censuring all the opinions that have been put forward on this obscure subject, one ought to propose some theory of one's own. I will therefore proceed to explain what I think to be the reason of the Nile's swelling in the summer time. During the winter, the sun is driven out of his usual course by the storms, and removes to the upper parts of Libya. This is the whole secret in the fewest possible words; for it stands to reason that the country to which the Sun-god approaches the nearest, and which he passes most directly over, will be scantest of water, and that there the streams which feed the rivers will shrink the most.
To explain, however, more at length, the case is this. The sun, in his passage across the upper parts of Libya, affects them in the following way. As the air in those regions is constantly clear, and the country warm through the absence of cold winds, the sun in his passage across them acts upon them exactly as he wont to act elsewhere in summer, when his path is in the middle of heaven- that is, he attracts the water. After attracting it, he again repels it into the upper regions, where the winds lay hold of it, scatter it, and reduce it to a vapour, whence it naturally enough comes to pass that the winds which blow from this quarter- the south and south-west- are of all winds the most rainy. And my own opinion is that the sun does not get rid of all the water which he draws year by year from the Nile, but retains some about him. When the winter begins to soften, the sun goes back again to his old place in the middle of the heaven, and proceeds to attract water equally from all countries. Till then the other rivers run big, from the quantity of rain-water which they bring down from countries where so much moisture falls that all the land is cut into gullies; but in summer, when the showers fail, and the sun attracts their water, they become low. The Nile, on the contrary, not deriving any of its bulk from rains, and being in winter subject to the attraction of the sun, naturally runs at that season, unlike all other streams, with a less burthen of water than in the summer time. For in summer it is exposed to attraction equally with all other rivers, but in winter it suffers alone. The sun, therefore, I regard as the sole cause of the phenomenon.
It is the sun also, in my opinion, which, by heating the space through which it passes, makes the air in Egypt so dry. There is thus perpetual summer in the upper parts of Libya. Were the position of the heavenly regions reversed, so that the place where now the north wind and the winter have their dwelling became the station of the south wind and of the noon-day, while, on the other hand, the station of the south wind became that of the north, the consequence would be that the sun, driven from the mid-heaven by the winter and the northern gales, would betake himself to the upper parts of Europe, as he now does to those of Libya, and then I believe his passage across Europe would affect the Ister exactly as the Nile is affected at the present day.