Page:The American Cyclopædia (1879) Volume IV.djvu/569

 CHRONOLOGY 557 long periods. The next longer obvious mea- sure is the interval between one new moon and another. It was found that this was about 29 days; and the month became the usual standard for measuring considerable spaces of time. But a larger definite measure was de- sirable for still longer periods. The round of the seasons appeared to furnish this; but, ignorant of the cause, men had no means of ascertaining the precise length of the year, or indeed if it had any certain length. Twelve months was an approximation to the average interval from harvest to harvest, and the year was at first made to consist of 12 months, al- ternately of 29 and 30 days, or 354 days. This being found too short, the year was lengthened to 360, and then to 365 days, various expedi- ents being adopted to make the lunar and solar years correspond, by intercalating the requisite number of days. In time it was found that a fractional part of a day was required to make up a complete year. By observing the inter- val between the periods when Sirius, the dog star, rose with the sun, the value of this frac- tion was found to be very nearly one fourth of a day. The year of 365J days was called the Sothic year, from the Egyptian name for Sirius, and sometimes the square or perfect year. It differs by less than 12 minutes from the true year as settled by the most accurate observations. Though known to astronomers long before, it appears not to have been used for chronological dates until the time of Julius Caesar. The old years of 354, 360, and 365 days were still employed for various purposes, and the commencement of the year was made to fall at different seasons. Hence has arisen much of the confusion which exists in the cal- endars of different times and nations. (See CALENDAK, DAT, and YEAH.) For a long pe- riod there was no fixed point of time from which dates were reckoned. Individuals would naturally count from the year of their birth ; monarchs from that of their accession, which is the notation of most ancient inscriptions. In course of time different peoples began to date from some event of national importance. The earliest of these fixed epochs is that of the Romans, who some centuries after that event began to date from the foundation of Rome. There was some question as to the exact time of this, some placing it in the year answering to our 753 B. 0., others in 751, 750, or 747. In Greece, the Olympic games became the event of paramount national interest. These games were celebrated every fourth year. But in retracing the succession of these Olympiads, when, perhaps in the 3d century B. C., it was deemed advisable to adopt them as an era, the victory of Coroebus was found to be the earliest recorded. Consequently the period of the games in which he was victorious was called the first Olympiad, and they were calculated to have taken place about 108 years after the restoration of the games by Iphitus, or about 776 B. C. An event occurring 775 years after the commencement of this era was set down as happening in the 3d year of the 193d Olympiad. Moreover, the original Grecian year consisted of 12 months of 29 and 30 days alternately ; and in order to make the lunar year accord with the solar, an intercalary month of 30 days was added, at first every second year, and subse- quently three times in eight years. This period of eight years, styled the octaeteris, contained 99 months, or 2,922 days, exactly equal to 8 years of 365J days, the Olympiads consisting alternately of 49 and 50 months. The three years (the 3d, 5th, and 8th) which had the in- tercalary month were styled embolismic years, and had 384 days, while the other five years had 354 each. But as a lunar month is some- what more than 29 days, the -octaeteris fell a little short of 99 months ; and to make up for this, three days were added to each alternate Olympiad ; but this made the solar year by so much too long. The error was allowed to go on for 40 Olympiads, by which time it had accumulated to 30 days, when a month was dropped, and the solar and lunar years again corresponded. Thus in a period of 40 Olym- piads there were four kinds of years: the com- mon, of 354 days ; the embolismic, of 384 ; the last of each alternate octaeteris, 387 ; and the last year of the 40th Olympiad, of 357 days. In the last year of the 86th Olympiad was in- troduced the Metonic cycle of 19 years, perhaps the greatest achievement of ancient astronomy, at the end of which each new moon comes back to the same day of the year. This continued in use as long as time was reckoned by Olym- piads, and is still used in determining the days upon which the movable feasts of the church will fall. The Babylonian era of Nabonassar, beginning at noon, Feb. 26, 747 B. C., has a special scientific interest from the fact that its commencement is astronomically determined to a minute. The year consisted of 12 months of 30 days each, to which 5 days were added at the end, so that 1,460 Julian years are equal to 1,461 Babylonian. The Mohammedans, the Persians excepted, reckon from the hegira, or flight of Mohammed from Mecca to Medina, July 16, A. D. 622. The Mohammedan year is strictly lunar, the civil months being adapted to the lunations by means of a cycle of 30 years, 19 of which have 354 days, and 11 have 355. Hence 30 Mohammedan years are equal to only 29 Julian years and 39 days. To convert a date of the hegira into the corresponding one of our notation, it is not sufficient to add 622, as is sometimes carelessly done. Thus the treaty between the emperor Charles VI. and the sultan is dated 1153 of the hegira; in- stead of 1775 of our era, it is 1740. The dif- ference increases nearly one year in 30. Since about 1530 the Mohammedans in India have dated from the hegira, but they use the solar year; hence their dates are now about nine years behind the Arabic and Turkish. The Persians do not date from the hegira, but from A. D. 632, the year of the accession of the