332 PHYSICAL SCIENCE 



water from within the earth, and it is in connection with this 

 opinion that he cites the experience of Nero's two centurions 

 above referred to, as if he were disposed to believe that what 

 these explorers saw was really a vast body of water issuing from 

 underground. 



The opinion of Thales is next criticised that the Etesian or 

 northerly winds drive the waters of the Mediterranean against the 

 mouths of the Nile and consequently pond back the waters of 

 the river. This view was of course entirely erroneous, but though 

 Seneca rejects it, he does not seem to have quite understood it, 

 for he argues that, coming from the same quarter as the winds, 

 the Nile water should not have been turbid, but clear and blue, 

 like that of the sea. In commenting upon the futile support 

 given by Euthymenes of Marseilles to the idea of Thales, Seneca 

 throws light on the wide extent to which the coasts of the outer 

 sea had then been made known by trading vessels. 



In rejecting another explanation proposed by Oenopides of 

 Chios, the author shows that he is aware of the fact that caves 

 and wells are warm in winter and cool in summer, and that he 

 has partly divined the reason, when he states that in winter they 

 are warm since they do not admit the frosty air from without and 

 in summer they feel cold because the warm air from outside has 

 not penetrated into their recesses. He returns to this subject in 

 Book VI. (24 1). 1 



After mentioning and dismissing a grotesque suggestion of 

 Diogenes of Apollonia, Seneca suddenly drops the discussion of 

 the Nile and passes on to the subject of hail. It is obvious that 

 there is here a serious gap in the text. It is not probable that 

 he meant to leave off his examination into the probable sources of 

 the Nile without stating his own view of a matter which had been 

 so long the subject of wonder and debate. Either, therefore, he 

 never completed this section of his treatise, or a portion of the 

 work has been lost. 



The remainder of Book IV. is taken up with a desultory 

 discussion of the subjects of hail and snow, written when the 

 author must have been in a somewhat frivolous mood. He 

 begins by telling Lucilius that if he were to assert that hail is 

 produced as ice is with us, a whole cloud being frozen, he would 

 be rather audacious. So he will imitate the chroniclers, who 

 after they have told a great many lies, refuse to be responsible 

 for some one statement, and refer for its truth to the authorities. 



1 The various ancient interpretations of the cause of the Nile's annual rise 

 are succinctly given by Lucretius (De Rer. Nat. vi. 712-37), but he does 

 not indicate a preference for any one in particular, though he devotes most 

 space to the influence of the Etesian winds. 



