i 4 2 PHYSICAL SCIENCE BK. in 



So when Lycus has been swallowed up by the yawning earth, 

 He comes forth far thence, and is born from another source. 

 So is now drunk up, now gliding with silent stream, 

 Is restored to its Argolic waves the mighty Erasmus. 



4 In the East as well as the West this happens. The 

 Tigris is absorbed by the earth and after long 

 absence reappears at a point far removed, but un- 

 doubtedly the same river. Some fountains cast 

 out their scourings at a fixed period ; the fountain 

 Arethuse does so every fifth summer during the 

 Olympic festival. Thence comes the belief that 

 the Alpheus makes its way right from Achaia 

 to Sicily, stealing under sea by secret sluice, and 

 reappearing only when it reaches the coast at 

 Syracuse. On that account, during the days on 

 which the Olympic festival is taking place, the dung 

 of the victims offered in sacrifice being thrown into 

 the stream of the river (Alpheus) turns up in 



5 quantity away in Sicily. You have yourself told 

 the story, my dear Lucilius, in your own poem, and 

 so has Virgil, who says in his address to Arethuse : 



So when thou glid'st beneath Sicilian seas, 



Never may sea nymph mingle bitter salt waves with thine. 



In the Carian Chersonese there is a fountain of 

 the Rhodians which at long intervals sends up 

 from its depths certain foul excretions of mud, until 



6 it is set free of them by being cleaned out. At 

 certain places wells throw up not merely mud but 

 also leaves, and bits of crockery and any other 

 filthy things that have accumulated in them. The 

 sea does the same everywhere, its nature being to 

 drive ashore all filthy impurities. In the neighbour- 

 hood of Messana and Mylae as it boils and tosses 

 in storms it throws up on the beach something 



