Then divide the day into three watches of eight hours each, and let each watch be presided over by one of the planet-gods: begin with Saturn. We then have Saturn as the first god ruling Saturday, and Jupiter and Mars, the two other gods, for that day. The first watch for Sunday will be the sun; Venus and Mercury will preside over the next two watches of that day. The planet that will preside over the first watch of the next day will be the moon, and the day will, therefore, be called Monday; Saturn and Jupiter will be the other gods for Monday. The first watch of the next day will be presided over by Mars, and the day will, therefore, be called Mars-day or Mardi, or, in the Teutonic languages, Tuesday, after Tuesco, a Scandinavian god of war. Mercury will give a name to Mercredi, or to Wednesday, or Wodin’s-day. Jupiter to Jeudi, or “Thurs” day. Venus to Vendredi, or in the Scandinavian, Friday, the day of the Scandinavian goddess Freya, the goddess of love and beauty, who corresponds to Venus, and thus the week is completed. [Illustration: FIG. 4.] This weekly scheme came probably from the Chaldean astronomers. It appears probable that the great tower of Babel, the ruins of which exist to this day, consisted of seven stages, one over the other, the top one painted white, or perhaps purple, to represent the Moon, the next lower blue for Mercury, then green for Venus, yellow for the Sun, red for Mars, orange for Jupiter, and black for Saturn. Unfortunately, of the colours no trace now remains. But nightly on the long terraces the Babylonian priests observed eclipses and other celestial phenomena. Their records were afterwards taken to Alexandria and kept in the great library that was subsequently burned by the Turks. In that library they were seen by the astronomer Ptolemy, who used them in the writing of his work on astronomy called the “Great Syntaxis” or “Collection.” The original work perished, but it had been translated into Arabic by the Arab astronomers, who called it “Al Magest,” the Great Book. It was translated from Arabic into Latin, and remained the textbook for astronomers in Europe quite down to the time of Queen Elizabeth, when a better system took its place. For the use of men engaged in practical astronomy, it is very convenient to consider the sun, moon, stars, and planets as going round the earth at rest. For instance, seamen use the heavenly bodies as in a way hands of a huge clock from which they can know the time and their position on the earth. “The Nautical Almanac,” which is printed yearly, gives the true position of these heavenly bodies for every hour, minute, and second of the year, and I will presently show how useful this is to sailors.