36 PITYSICAL GEOGRAPHY OF TITE SEA. 
reventy years after this involuntary discovery, the Phoceans of 
Massilia, or Marseilles, first ventured to follow on the track of 
Coleus for the purpose of trading with Tartessus, the present 
Cadiz; and from that time remained in constant commercial 
intercourse with that ancient Phcenician 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 Red 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 seais 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, that Pytheas 
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, aud Cesar says positively (Commen- 
taries, De 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 
