Before the introduction of the hour, the day and night appear to have been divided into watches. Among the Babylonians the night was reckoned from what we call 6 A.M. to 6 P.M., and divided into three watches of four hours each--called the "evening," "middle," and "morning" watch. These were later superseded by the more accurate hour, or rather "double hour" or _casbri_, each of which was divided into sixty minutes and sixty seconds, and the change taking place not earlier than 2,000 B.C. Whether the Babylonians (or Accadians) were the inventors of the hour it is difficult to say, though they almost certainly were of other divisions of time. It is remarkable that in the ancient Jewish Scriptures we find no mention of any such division until the date at which the prophecy of Daniel was written, that is, until the Jews had come in contact with the Babylonians. Some nations have counted the twenty-four hours consecutively from one to twenty-four as astronomers do now, but others and the majority have divided the whole period into two of twelve hours each. The time of the commencement of the day has varied much with the different nations. The Jews, the ancient Athenians, the Chinese, and several other peoples, more or less of the past, have commenced the day with the setting of the sun, a custom which perhaps originated with the determination of the commencement of the year, and therefore of the day, by the observation of some stars that were seen at sunset, a custom continued in our memory by the well-known words, "the evening and the morning were the first day." The Italians, till recently, counted the hours in a single series, between two settings of the sun. The only gain in such a method would be to sailors, that they might know how many hours they had before night overtook them; the sun always setting at twenty-four o'clock; if the watch marked nineteen or twenty, it would mean they had five or four hours to see by--but such a gain would be very small against the necessity of setting their watches differently every morning, and the inconvenience of never having fixed hours for meals. Among the Babylonians, Syrians, Persians, the modern Greeks, and inhabitants of the Balearic Isles, &c., the day commenced with the rising of the sun. Nevertheless, among all the astronomical phenomena that may be submitted to observation, none is so liable to uncertainty as the rising and setting of the heavenly bodies, owing among other things to the effects of refraction. Among the ancient Arabians, followed in this by the author of the _Almagesta_, and by Ptolemy, the day commenced at noon. Modern astronomers adopt this usage. The moment of changing the date is then always marked by a phenomenon easy to observe.