CHRONOLOGY, the science of dates, or of arranging events in order of time. Two steps in human progress were requisite for its exist ence: the invention of material records, since memory would not transmit exact sequences of events on any considerable scale; and the adop tion of some recurrent astronomical period, neither too short nor too long, as a measure of time. The pictograph, developed into a system of writing, and the Peruvian quipu, or knotted cord, are the chief of the former. The fixing of the year by the Babylonian astronomers was the only feasible specimen of the latter; the month being too short for a measure of long periods and even the year becoming too formi dable in numbers for the limited counting power of the ancients. Between the creation of these raw materials, however, and the construction of a simple and universally applicable system for even one country, thousands of years elapsed in which the chaos of unsystematic systems is still the difficulty and often the despair of antiquarians.
For a satisfactory chronology there is a third requisite,— a fixed epoch to count from, no matter what: as in Babylonia the accession of Nabonassar; in Greece the hypothetical institu tion of the Olympian games; in Rome the imagi nary foundation of the city; in Christendom the arbitrarily fixed birth of Christ; with the Mo hammedans the Hegira of the Prophet, etc. But, obvious as this seems, it is in fact a very late device of civilization. Herodotus and Thucy dides, in the most splendid intellectual age of Greece, wrote history without' a date, or any apparent recognition that one was needed. The sequence of events was preserved; but that these need be related to an arbitrary point in the past is an artificial conception, created by the ac cumulation of practical inconveniences. These would seem to have differed in each country which independently invented it: the scientific and business ones in Assyria, historical in Greece, administrative in Rome. Others bor rowed the system when its utility was manifest; but older societies were satisfied with a ruder scheme. Their science and business was alike undeveloped; their historical sense was satis fied with a few dramatic episodes, and even the order of events was heroically confounded; and when it became necessary to keep public rec ords, their unit was a reign, or they dispensed with units altogether and dated by some notori ous event. Thus the Babylonians dated their business and official tablets "the year he brought Nannar of Nippur into a house," 'the year he overran Karkhar,' 'the year he overran Kark har a second time," 'the year divine Bur Sin became king,' etc.; on exactly the same princi
ple as a modern mother dates events in the year the second child had the measles. Dating by the year of a certain Icing's reign is a natural system, still preserved in English statutes: they are not the laws of 1663 or 1860, but .4th Car. II,' "24th Victoria,' etc.
In Assyria, as early as the 14th century s.c., a system was begun of dating by °eponyms," or the names of the chief officers of state, in an nual succession, with the chief events in the year; each new king's name being entered on his accession. Thus: "Edsur-sarabe governor of Gozan. Revolt in city of Ashur. In month Sivan sun was eclipsed.* (Three intervening entries). "Pan-ashur-lamur governor of Ar bela. Revolt in city of Gozan. Pestilence.* In Rome, it was "in the consulate of* certain persons; in Athens, "in the archonship of'; and so on. Obviously, if the regular succession of functionaries is preserved for a long time, as Assyria it was for centuries, it will furnish a perfect chronology provided one date can be fixed in the series. This has been done in sev eral cases, and the chronology of some sections of ancient history has been accurately recon structed over long periods. The most certain authentication is by some astronomical phe nomenon whose date can be fixed by calcula tion; and several of these priceless data are casually mentioned by old records or historians. Thus, the mention by an Egyptian papyrus of a rising of Sirius, in connection with the over flow of the Nile, fixes the accession of Userte sen III, fifth king of the •12th dynasty, between 1876 and 1873 ri.c.; the oldest certain year-date or approximate date in history yet discovered, and by a happy chance, in a country the most empty of chronological data. (The Babylonian Naram-Sin's date as near 3750 B.C. is now quite discredited). The most usual of these phe nomena recorded are eclipses of the sun, from the terror inspired by the darkening of the sky; fortunately for history, as the mention of them has furnished several invaluable dates. The Assyrian eponym canon for several centuries has been fitted with accurate dates by the eclipse recorded in the first entry above, 763 ac.; the same one is mentioned in the Bible Amos viii, 9) as occurring in the reign of Jeroboam II. Even when we cannot be certain by itself which eclipse was meant, it is rare that other synchronisms do not fix the limit. Thus, an important date in the kingdom of Lydia is determined by an eclipse which was either 610 or 585 B.C., and other circumstances make the latter date probable.