are twelfth parts of the artificial day and night; being each double in length to the hour used in civil computation in Europe. They are still used by the Jews as they were among their forefathers; and hence are called Jewish hours. The reason of their being called planetary hours, is, that, according to the astrologers, a new planet comes to predominate every hour, and that the day takes its denomination from that which predominates the first hour of it; as Monday from the moon, &c.