From 645 A.D., under, the mikado Kōtoku, the system of reckoning the years by chronological periods called nen-gō, or year-names, has been in use. In historical works, and in Japanese literature generally, these year-periods are always referred to, and formerly many natives committed the entire list to memory. Others used little reference - tables, kept in their pocket-books or near at hand. No special rule or system was observed in changing the names, though the accession of a new sovereigm, the advent of war or peace, a great national calamity or blessing, a profound social change or great national event, was made the pretext for adopting it new name. It thus results that from 645 to 1868 A.D. there have been 249 year-names, including those used by the "northern dynasty" during the period 1836-1392, treated of in Chapter XIX. The year-names are appointed by the mikado, and are chosen from sixty-eight Chinese words or characters specially reserved for that purpose. They are often very poetic and striking. (See in Dr. J. J. Hoffman "Grammar", page 157.) In the following list, it will be noticed that the same syllables recur often. The dates can not exactly correspond to out years, since the Japanese New-year's-day was often as much as six weeks later than January 1st. A few years ago - 1872 - the Government fixed upon the year 660 B.C. as that in which Jimmu Tennō "ascended the throne," and Christmas, December 25th, as the day. Hence, in the newspapers, official documents, and books printed since 1872, the time is expressed in "years of the Japanese empire," or "from the foundation of the empire," or "from the accession of Jimmu Tennō." These phrases have a value at par with the Roman "Ab urbe condita," the date of Jimmu's "ascension" being purely arbitrary.