Corpus of Electronic Texts Edition
An Irish Astronomical Tract (Author: [unknown])

Caibidil 12



Some of the ignorant declare that the flood of the river Nile is caused by the great rains that fall in distant lands, and as the river fills, it bursts forth throughout the land of Egypt, and what rain does for the other races, the water of the river Nile does for the Egyptians. I declare that they have no argument or reason to prove that statement, except one single theory, because, as they see the other rivers of the world becoming swollen by rains, they think that the river Nile is thus swollen.

I will now prove that that theory is false, because if the rains were the cause of the flooding of the river Nile, as they declared, it would become swollen, with no special period for its filling, every time it should rain heavily throughout the year as the other rivers become swollen. It is clear to everyone who sees it that that river does not become swollen except at a particular time of the year, i.e., in the month of August; but when there is a plentiful fall of rain in some district near Egypt that river becomes slightly swollen on account of that rain, because rain that falls in districts distant from Egypt never increases the river Nile on account of the great distance of the source of the river from Egypt, and of the exceeding dryness of the soil. Consequently, at whatever period of spring or summer or any other season rain falls, the sandy, very dry soil and the parching of the sun absorbs the rain water, and does not allow it advance to the river; or, when the river is swollen from excessive rain together with the great sudden floods, the heat of the earth around the river is so great, that no sooner are the floods at their full, than the earth absorbs them. The water in that river is seldom accidental, and it is always filled bank to bank with its own water.

As a proof of that: if you made a trench two or three hundred miles long through the dry earth, although you might pour a great amount of water into one end of it, the earth would absorb it all before one drop would reach the other end of it; thus does the parched, hot soil of the river Nile absorb the waters that fall around it before they reach Egypt; consequently rain is not the cause of the flooding of the river Nile.

Another fact to prove the same thing as I heard from my own elders78: the Egyptians thought at one period that the river Nile would not rise until the fairest maiden of greatest beauty in Egypt should be cast into it, and because they were obliged to get the overflow of the river to moisten the earth, since that is what they have instead of rain, they used to cast the most beautiful maiden that could be found in the whole land into the river in the beginning of the month of August, and the hour after that the river used to be filled, not on account of the woman being cast into it but because its own time had come, and it used to fill all Egypt around it. And this kind of evil practice was in vogue in Egypt until the time of Omar, King of Egypt. As he saw her die by


that rude, sinful, evil custom in the beginning of the month of August, he composed a short letter79, and said in it, ‘In the name of the merciful Lord, Thomarus,80 King of Egypt; Life and health to the river Nile, and if it be thy will 0 River Nile, through the powers of God to pour thy water on the land of Egypt, we pray thee do so now; and if it be not thy will, we have no reliance in thee.’

He put the letter then into the river, yet not on account of the letter nor on account of the woman, but because its own time had come, it overflowed its banks mightily and filled Egypt. Consequently, if that flood resulted from those rains, since rain falls frequently during the year, the river would become swollen frequently. Thus as that theory is false, I shall disclose the true cause of the flood of the river Nile.

I declare that the source of the river is between the east of the world and the southern quarter; between the west of the world and the northern quarter, it enters the sea. The atmosphere of Egypt is warm and dry, so that it but seldom admits wind or clouds or rain to exist in it. For although the surrounding countries experience wind, that air condenses and contracts, so that it is accompanied by a very great storm that clouds or rain enter the boundary of that air, and when it enters—which is seldom—there is terrible thunder and very great wind and lightning, which kills the flocks of Egypt. It is the nature of air in general to spread and expand, when it becomes warm; and when it grows cold to press together, and it contracts and draws towards it everything like unto it. The sea air is colder in the night than in the day, consequently, when the sun reaches its mid-day position, through the heat of the sun the air spreads and expands and the wind blows from that time until midnight into the mouths of the rivers which flow westwards into the sea, and (the wind) opposes the rivers, and drives them forcibly back, and does not permit them to flow into the sea until the cold of the night lessens the strength of the heat of the sun; and, consequently, the conflict with the streams results from the heat of the atmosphere and the flowing into the sea from the coldness of the atmosphere. As the sea air is warmer in the day than in the night, and it is owing to the proximity of the sun to us and its distance from us that that change comes over the atmosphere; thus, at the time of the year the sun is nearest to us, i.e., the summer, the sea air is hottest. Consequently on the first day of the month of May until the sun enters the September equinox the sea-breeze blows eastwards towards Egypt over the river Nile, and joins with the air of Egypt to set it in motion and expel it from its own place.

Since that air is dry, heavy, and difficult to move, it opposes the wind and does not abandon its own place, and since the wind that is always blowing finds no other course,


it turns the river Nile forcibly back, and does not allow a drop of it to enter the sea, and the same wind sweeps much of the sea sand forcibly into the mouth of the river Nile.

Consequently, since the river is prevented from flowing into the sea, it becomes flooded throughout Egypt, and that flood continues as long as the wind has its own force, i.e., during the time I have just mentioned, from the first day of May until the September equinox. Then the wind begins to lose its strength, and the sun leaves its position directly over the sea, and sinks by degrees in the southern quarter of the world. When the water of the river finds no opposition from the wind as it did up to this, it breaks the mountain of sand and proceeds on to the sea and departs from Egypt; and then the Egyptians plough and sow, since they are certain that the river will not hinder them until that season again. Consequently, it is evident that they would be often hindered earlier than that season if the flood of the river Nile resulted from rains.

The rivers of the other lands which flow into the Western sea experience the same flooding although it does not happen to them so much as it does to the river Nile, for there is only weak movable air, that does not contend with the wind, and moves in every direction in which it is carried into the other lands. On that account no other river in (other) countries is as wide as the river Nile at its flood; and may He who created the river Nile be blessed forever in saecula saeculorum.