174 PHYSICAL SCIENCE UK. iv 



peaks where they rise the snow lies very deep. 



20 The Phasis, too, and the Dnieper would swell 

 during summer if snows had the power of rais 

 ing 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 soft 

 ness the thaw is quickest. The Nile, however, has 

 a regular increase to its stream during four months. 



21 If one may believe Thales, the Etesian winds 

 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. Euthy- 

 menes of Marseilles 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 



22 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. 



23 Then, again, the Etesian winds beat on the shore of 

 Egypt, and the Nile comes down in their teeth : 



