36 PHYSICAL GEOGBAPHY OF THE SEA. 



seventy years after this involuntary discovery, the Phoceans of 

 Massilia, or Marseilles, first ventured to follow on the track of 

 Colseus for the purpose of trading with Tartessus, the present 

 Cadiz , and from that time remained in constant commercial 

 intercourse with that ancient Phoenician colony. 



With what eager attention may their countrymen have 

 listened to the wondrous tale of the alternate rising and sinking 

 of the ocean ! Such must have been the astonishment of our 

 forefathers when the first Arctic voyagers told them of the 

 floating icebergs, and of the perpetually circling sun of the 

 high northern summer. 



Thus the tides became known to the Massilians about five 

 centuries before Christ, but in those times of limited interna- 

 tional intercourse, knowledge travelled but slowly from place to 

 place ; so that it was not before the conquests of Alexander, 

 which first opened the Eed Sea and the Persian Gulf to Grecian 

 trade, that the great marine phenomenon began to attract the 

 general attention of philosophers and naturalists. 



The flux and reflux of the sea is evidently so closely connected 

 with the movements and changes of the moon, that the intimate 

 relations between both could not possibly escape the penetrating 

 sagacity of the Greeks. Thus we read in Plutarch, thatPytheas 

 of Marseilles, the great traveller who sailed to the north as far as 

 the Ultima Thule, and lived in the times of Alexander the Great, 

 ascribed to the moon an influence over the tides. Aristotle ex- 

 pressed the same opinion, and Caesar says positively (Commen- 

 taries, Be Bel. Gal. book iv. 29,) that the full-moon causes 

 the tides of the ocean to swell to their utmost height. Strabo 

 distinguishes a three-fold periodicity of the tides according to 

 the daily, monthly, and annual position of the moon, and Pliny 

 expresses himself still more to the point, by saying that the 

 waters move as if obeying the thirsty orb which causes them 

 to follow its course. 



This vague notion of obedience or servitude was first raised 

 by Kepler to the clear and well defined idea of an attractive 

 power. According to this great and self-taught genius, all 

 bodies strive to unite in proportion to their masses. " The earth 

 and moon would mutually approach and meet together at a 

 point, so much nearer to the earth as her mass is superior to 

 that of the moon, if their motion did not prevent it. The moon 



