strange, but colossal—­the rhinoceros, the hippopotamus, the camel, the crocodiles of the Nile and the Ganges.  They had encountered men of many complexions and many costumes:  the swarthy Syrian, the olive-colored Persian. the black African.  Even of Alexander himself it is related that on his death-bed he caused his admiral, Nearchus, to sit by his side, and found consolation in listening to the adventures of that sailor—­the story of his voyage from the Indus up the Persian Gulf.  The conqueror had seen with astonishment the ebbing and flowing of the tides.  He had built ships for the exploration of the Caspian, supposing that it and the Black Sea might be gulfs of a great ocean, such as Nearchus had discovered the Persian and Red Seas to be.  He had formed a resolution that his fleet should attempt the circumnavigation of Africa, and come into the Mediterranean through the Pillars of Hercules—­a feat which, it was affirmed, had once been accomplished by the Pharaohs.

Intellectual condition of Persia.  Not only her greatest soldiers, but also her greatest philosophers, found in the conquered empire much that might excite the admiration of Greece.  Callisthenes obtained in Babylon a series of Chaldean astronomical observations ranging back through 1,903 years; these he sent to Aristotle.  Perhaps, since they were on burnt bricks, duplicates of them may be recovered by modern research in the clay libraries of the Assyrian kings.  Ptolemy, the Egyptian astronomer, possessed a Babylonian record of eclipses, going back 747 years before our era.  Long-continued and close observations were necessary, before some of these astronomical results that have reached our times could have been ascertained.  Thus the Babylonians had fixed the length of a tropical year within twenty-five seconds of the truth; their estimate of the sidereal year was barely two minutes in excess.  They had detected the precession of the equinoxes.  They knew the causes of eclipses, and, by the aid of their cycle called Saros, could predict them.  Their estimate of the value of that cycle, which is more than 6,585 days, was within nineteen and a half minutes of the truth.

Intellectual condition of Persia.  Such facts furnish incontrovertible proof of the patience and skill with which astronomy had been cultivated in Mesopotamia, and that, with very inadequate instrumental means, it had reached no inconsiderable perfection.  These old observers had made a catalogue of the stars, had divided the zodiac into twelve signs; they had parted the day into twelve hours, the night into twelve.  They had, as Alistotle says, for a long time devoted themselves to observations of star-occultations by the moon.  They had correct views of the structure of the solar system, and knew the order of the emplacement of the planets.  They constructed sundials, clepsydras, astrolabes, gnomons.