_Day_--The subdivision of the day into twenty-four parts or hours has prevailed since the remotest ages, though different nations have not agreed either with respect to the epoch of its commencement or the manner of distributing the hours. Europeans in general, like the ancient Egyptians, place the commencement of the civil day at midnight; and reckon twelve morning hours from midnight to midday and twelve evening hours from midday to midnight. Astronomers, after the example of Ptolemy, regarded the day as commencing with the Sun's culmination, or noon, and find it most convenient for the purpose of computation to reckon through the whole twenty-four hours. Hipparchus reckoned the twenty-four hours from midnight to midnight. The Roman day, from sunrise to sunset, and the night, from sunset to sunrise, were each divided at all seasons of the year into twelve hours, the hour being uniformly one-twelfth of the day or the night, of course, varied in length with the length of the day or night at different seasons of the year. _Week_--Although the week did not enter into the calendar of the Greeks, and was not introduced at Rome till after the reign of Theodosius, A. D. 292, it has been employed from time immemorial in almost all Eastern countries; and as it forms neither an aliquot part of a year nor of the lunar months, those who reject the Mosaic recital will be at a loss to assign to it an origin having much semblance of probability. In the Egyptian astronomy the order of the planets, beginning with the most remote, is Saturn, Jupiter, Mars, the Sun, Venus, Mercury, the Moon. Now, the day being divided into twenty-four hours, each hour was consecrated to a particular planet, namely: One to Saturn, the following to Jupiter, third to Mars, and so on according to the above order; and the day received the name of the planet which presided over its first hour. If, then, the first hour of a day was consecrated to Saturn, that planet would also have the 8th, the 5th and the 22d hours; the 23d would fall to Jupiter, the 24th to Mars, and the 25th or the first hour of the second day would belong to the Sun. In like manner the first hour of the third day would fall to the Moon, the first hour of the fourth to Mars, of the fifth to Mercury, of the sixth to Jupiter and the seventh to Venus. The cycle being completed, the first hour of the eighth day would again return to Saturn and all the others succeed in the same order. See table on the 17th page.