Still another cause of the imperfection of early chronological methods was the difficulty found by the masses in grasping large numbers. Hence,. it became the practice to divide the time into cycles of a small number of years, and number by the years in a cycle. The Olympiad was• a refined form of this. Our own system of reckoning by centuries is another, only by its decimal form it expresses both ideas at once. Instead of saying *the 3d year of the 20th cen tury,* as *the 3d year of the 40th Olympiad? we use a term of addition, and say *nineteen hundred(s) and three.* The Chaldwans had their saros• of 6,585Y3 days, or 18 years; the Romans, their indiction of 15; and the Chinese and other Asiatic nations still use a cycle of 60. The European cycles, however, as the metonic of 19 years still used for computing Easter, were mostly used to regulate the calendar rather than to compute dates; but they are often extremely useful as an additional method of verifying these.
Babylonian: Era of Nabonassar.-- This prince seems for a very brief time to have thrown off the Assyrian yoke and restored Babylonian independence. It was almost imme diately but he succeeded in imposing a new dating system which convenience main tained, or else later gratitude looked back to him, under, the glories of Nabopolassar and Nebuchadnezzar, as the pioneer of Neo-Baby lonian greatness. At any rate, the era is fixed at 26 Feb. 747, from astronomical data collected in Chaldra by Callisthenes, a general of Alex ander- the Great. It is the basis of the once famous Canon of Kings, or Mathematical Canon, preserved in Ptolemy's works, and pre vious to the era of archieologv our one source of Mesopotamian history. The Alexandrian Greeks also used this era till their adoption of Julius Caesar's reformed calendar, 25 a.c. The Babylonian year was different in length from the Julian of 3653 days, and the conversion of Nabonassar years into years a.c. is a matter of delicacy, necessitating a knowledge of the month and day, for certainty. Tables have been drawn up, for this purpose.
Olympiads.— It is now pretty generally ad mitted that the early lists of victors in the Olym pic games are fictitious, and that the foundation of the games cannot be assigned a date, our first authentic knowledge beginning with the 6th century ti.c.; but this is indifferent to the method of calculation which assunies a beginning in 776 a.c. They were celebrated every fourth year in the summer solstice; and as the Olympic year began sometimes with the full moon before and sometimes with the one after the solstice, to save trouble and perpetual recomputation it was reck oned as beginning the 1st of July. Hence, the
Olympic years cannot be synchronized with ours year by year: the second half of the one corre sponds with the first half of the other, and the month must be known for accurate conver sion. Therefore, in years before Christ, when the event happened between January and June, inclusive, subtract the number of the Olympic year from 776. Thus: the oligarchy of the Four Hundred was desposed in June 01 xcii, 1: 4 X 91 + 1=365; 776— 365=411 B.C. Socra tes was executed in May 01. xcv, 1: 4 X 94 + 1=377; 776— 377=379 B.c.. If it took place in the latter part of the year (as did the immense majority of the familiar incidents in Greek his tory—all the great battles, for physical reasons, the deaths of Pericles and Cleon, etc.), subtract the sum as aforesaid from 777. Thus, the bat tle of Platxa was fought in September 01. lxxv, 2: 4 X 74 + 2=298; 777— 298=479 sc. If the year is after Christ, subtract the number of the Olympic year from 776 in the first case, from 777 in the second. The Olympiad was only used by historians ; it is never found on coins or inscriptions. A new Olympiad was instituted by the Roman emperors, beginning with 131 A.D., and is used on some coins and inscriptions, but struck no deep root.
Macedonian Era, or Era of the Seincidse: also called by the Jews Era of Contracts, be cause their Syrian governors compelled them to use it in civil business, and styled by the writers of the books of Maccabees the Era of Kings.—This epoch dates from the foundation of the Syro-Mesopotamian monarchy by Seleu cus Nicator, Alexander's general; assumed to begin with his occupation of Babylon 311 B.c4 12 years after Alexander's death. It was used not only in the Seleucid empire, but by the Greek states on the east coast of the Mediter ranean generally; was followed by the Jews till the 15th century, and is said to be in use by some Arabians even yet. It was the great Eastern date for many centuries, but it is one of the most difficult to convert into terms of Christian years, from the astonishing variety in the beginnings of the year (which in different countries and among different sects varied from the vernal equinox to 28 October), and from the variation in length of year, some using the Egyptian year of 365 days, some the Julian of The -usual computation is' to place the beginning of 312 Seleucid on 1 September in the Julian year preceding the first of our era. Therefore, to reduce a Seleucid 'date to ours, subtract 311 years 11 months.