Chronology (Gr.Chronology 0400267 fromChronology 0400268 time, and λoyoς, discourse), the science of establishing historical dates, by arranging events in the order of their succession, and determining the interval between each and some fixed period in time. We are so accustomed to the facility with which this is accomplished by means of the Gregorian calendar and the conventional fixed point of the Christian era, that we can hardly appreciate the obstacles which have been overcome in order to bring the science to its present state. It was necessary at the outset to find some tangible standard by which to measure the intangible element of time. The most obvious measure is the day, or regular interval between one apparent rising or setting of the sun and another. This, though exact as far as we can know, is so short as to be inconvenient when applied to long periods. The next longer obvious measure is the interval between one new moon and another. It was found that this was about 29 1/2 days; and the month became the usual standard for measuring considerable spaces of time. But a larger definite measure was desirable 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, alternately 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 expedients 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 interval between the periods when Sirius, the dog star, rose with the sun, the value of this fraction was found to be very nearly one fourth of a day. The year of 365 1/4 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 calendars of different times and nations. (See Calendar, Day, and Year.) - For a long period 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. C., 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 subsequently 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 365 1/4; days, the Olympiads consisting alternately of 49 and 50 months. The three years (the 3d, 5th, and 8th) which had the intercalary month were styled embolismic years, and had 384 days, while the other five years had 354 each.

But as a lunar month is somewhat more than 29 1/2 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 Olympiads there were four kinds of years: the common, 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 introduced 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 Olympiads, and is still used in determining the days upon which the movable feasts of the church will fall. The Babvlonian 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 liegira, 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; instead of 1775 of our era, it is 1740. The difference 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. I). 632, the year of the accession of the shah Yezdegird; their year consists of 305 days, and they have a complicated but very accurate system of intercalation. This era is also used by the Parsees of India. The Armenians date from July 9, 552, the year of the council of Tiben, which, by condemning the decrees of the council of Chalcedon, formally separated the Armenian from the Greek church. The Hindoos use both the sidereal and the solar year, and employ the eras of Kaliyug, 3101 B. C, the Vicramaditva, 56 B. 0., the Salivahana, A. D. 78, and the Fuslee, about A. D. 590. The Chinese have a complicated calendar.

For chronological purposes they employ a series of yearly, monthly, and daily cycles of 00. Each year, month, and day has its own name in its cycle. By compounding these names, a single word expresses the year, month, and day. The year 1864 was the first of a cycle, so that 1873 is its 10th year. The character denoting a cycle first appears at 2357 B. C, and this is noted as the 41st year of the cycle, so that the epoch of this cycle would be 2397 B. C, which is accepted by the authors of the Art de verifier les dates; but the Chinese mathematical tribunal has from time immemorial begun this cycle with 2277 B. C, apparently assuming that there had been a dating back in the records. For more than 20 centuries Chinese historians have dated from the year of the accession of the reigning emperor. A particular name, not necessarily that of the sovereign, is given by authority to each reign, and the years are numbered 1, 2, 3, and so on; a register of these eras is kept, by aid of which the chronological year may be ascertained; just as to determine the date of an English statute, we must know the year in which the sovereign under whom it was enacted began to reign.

The Jews, whose calendar is that of the ancient Greeks in its perfected form, date from the creation, which according to their usual computation took place in 3700 B. C. The Russians date ecclesiastically from the creation, which, according to their computation of the dates in the Septuagint, took place 5508 B. C. Historically they use the common Christian era, but adhere to the old style of 365 1/4 days to the year, which is nearly 12 minutes too long, the difference amounting to not quite a day in a century. In 1700 the variation was 11 days, in 1800 it became 12, and will so continue till 1900, when it will be 13, and will remain so until 2100, when it will be 14, should the Russians then adhere to the old style. - When Christianity became predominant in the civilized world, writers began to date from various epochs in the history of the Saviour. About the middle of the 6th century DionysiusExiguus, a Roman abbot of Scythian birth, introduced the method of dating from the birth of Christ, which according to his computation took place in the 4th year of the 194th Olympiad, the 753d from the foundation of Rome. It is generally conceded that he placed this event about four years too late; this is however of no importance in chronology, as it merely involves the necessity of placing the date of the birth in the year 4 B. C. Dionysius began his year with the Annunciation, the 25th of March, nine months before the day which is now considered to be that of the birth of Christ; so that his era, which continued in use for some centuries, is by so much in advance of that now in use.

Christmas and Easter were also sometimes taken as the commencement of the year. These differences occasion some apparent discrepancies in dates during the middle ages. Thus, Charlemagne was crowned on Christmas day, 800, and died Jan. 28, 814, reckoning the year to begin on the 1st of January. But the chronicle of Metz says that he was crowned on Christmas day, 801, and the chronicle of Mois-sac that he died in January, 813. Although there is an apparent variation of two years, the same day is meant in every case. The Metz chronicle begins the year with Christmas day, so that the remaining days of December belong to 801; the Moissac chronicle begins the year with the annunciation, and the days from Jan. 1 to March 25 belong to 813. Had the coronation taken place a week and the death two months later, the dates by all these modes of reckoning would have been the same. So, too, in all dates previous to 1582, it must be noted whether they are given in the old style or have been reduced to the new, as is usually done in modern chronology. - Could the precise time of the creation be ascertained, it would be the natural starting point from which to date.

But the history of ancient nations, unless we make an exception in the case of the Hebrews, goes back into mythical periods of thousands or millions of years; and even after the records begin to assume a historical aspect, the discrepancies are very great. The Hindoo chronology, as computed by Gentil, reaches to 0,174 years before the Christian era; the Babylonian to 0,158, and the Chinese to 0,157, according to Bailly. About 200 different computations have been made, based upon the Hebrew, Septuagint, and Samaritan texts of the Bible. The longest is one by Regiomontanus, 6,984 years; next that of Clement of Alexandria, 5,624; the most accredited one based on the Septuagint is 5,508; that by Usher, from the Hebrew, is 4,004, which the Jews reduce still further, the lowest, by Rabbi Lipmann, being only 3,616 years. The main cause of these discrepancies is the different numbers given in the Septuagint and the Hebrew texts. There is a Samaritan text of the Pentateuch which differs from both; but this is now admitted to be of no authority. Josephus also gives dates, but he is altogether too careless to be taken into account.

The main variations between the Septuagint and the Hebrew are found in the two periods from Adam to the flood, and from the flood to the call of Abraham. For the former period both give the same list of 10 generations in direct succession, with the entire life of each patri-arch, in which they agree; and his age at the birth of the son by whom the succession was carried on, which gives the total length of the period, wherein they differ widely. The two statements stand thus:

1PATRIARCHS.

BEFORE BIRTH OF HEIR.

Total Age in both.

Hebrew.

Septuagint.

Adam.....

130

230

930

Seth..............

105

205

912

Enos.....

90

190

905

Cainan......

70

170

910

Mahaleel......

60

165

895

Jared......

162

162

962

Enoch.....

65

165

365

Methuselah......

187

187

969

Lameeh......

182

188

777*

Noah (at flood).........

600

600

Time of the flood......

1,656

2,262

There are various means of explaining this difference of 606 years. Modern scholars give the preference to the following of Bockh. The 2,262 years of the Septuagint are considered an attempt on the part of the 70 interpreters at reducing the 1,656 years of the Hebrew text to 19 Sothic cycles, which are equal to 27,759 Egyptian years, or to as many months of 29 1/2 days, in all 818,8901 days, and which are equal to 2,242 Julian- or Sothic years. This Sothic year, which differs from the Julian in the day of commencement alone, seems to have been the year of the priests, and its early use by the Egyptians is shown on a calendar sculptured on the exterior of the temple of Medinet Abu at Thebes. But supposing the Hebrew figures proved genuine, there remains the difficulty of proving them historical. They place the time of the flood at about 2340 B. C. Both the Babylonian and Egyptian histories represent powerful monarchies as existing about or before that date. Sir Gardner Wilkinson places the beginning of the 4th Egyptian dynasty at 2450, and this was preceded by several others. Rawlinson places the foundation of the Chaldean monarchy at about 2286. Others carry these dates still further back.

This difficulty may indeed be got over by assuming the Egyptian and Babylonian chronologies to be erroneous. But the Hebrew dates seem to be inconsistent with historical events narrated in connection with them. According to the present text, Abraham was born not quite 300 years after the flood, when the whole human family consisted of but eight individuals. Yet it is clear from the narrative that in his day the whole region from the Euphrates to the Nile was densely peopled. There were also powerful kingdoms east of the Euphrates; for wo find Chedor-laomer, king of Elain, that is, of southern Persia, with three allies, making military expeditions to the valley of the Jordan. Now a period of about 376 years from the flood to the migration of Abraham to Canaan is altogether too short to allow such an increase of the human race, according to any known law of the growth of population. If we assume the Septuagint period of 1,147 years, this difficulty is obviated, and the chronology approximates to that of the Egyptians, Babylonians, and Chinese. It is safer, upon the whole, to consider the entire chronology of the world to be uncertain up to about the time of Abraham. From that time the chronologist begins to tread upon firm ground, the Hebrew dates being clear and definite within a few years.

The exodus from Egypt is well fixed at 440 years after the migration of Abraham. From the exodus to the completion of Solomon's temple the Hebrew text gives 480 years, the Septuagint 440. An attempt has indeed been made to extend this period by about 150 years; but it seems to be based upon insufficient data. From the time of Solomon Hebrew chronology becomes fairly connected with that of Egypt, Assyria, and Babylonia, and the dates of each are confirmed by the others. Chinese and Hindoo chronology is fairly credible to about 2200 B. C. Greek and Roman dates are generally well authenticated to the 1st Olympiad and the establishment of the consulate, previous to which they are mainly traditional or legendary. From the Christian era to our own times the date of nearly every important event is settled beyond question within a year or two. - The materials for the chronologist consist of original monuments, such as inscriptions, coins, and the papyri found on Egyptian mummies, and of written records either contemporaneous with the events or handed down through a succession of writers.

Inscriptions and coins have a special value, as they are usually made by public authority, and in any case exist in their original state; whereas in successive transcriptions or quotations there is always a possibility of error. The Assyrian, Babylonian, and Egyptian inscriptions are in extinct languages and in characters long obsolete. For the means by which these have been deciphered, see Cuneiform Inscriptions, and HIEROGLYPHICS. The written records of Egypt, besides the papyri, come through Manetho, who lived about 300 B. C, and professes to have made use of original authorities. Of his work we have only fragments preserved in citations by later Greek writers. The written history of Babylonia, besides the inscriptions and tablets, comes mainly through Berosus, who wrote about 260 B. C.; of his work also only fragments are extant. Ctesias, a Greek, about 415 B. C, wrote a history of Babylonia, but it is not regarded as authentic. Herodotus is valuable only as to events of his own time, about 450 B. C, and those of a century or two earlier. - Attempts have been made to bring astronomy to the aid of chronology. Eclipses being anciently regarded as portents, occasional mention is made of them in connection with historical events.

Thus Herodotus says that a battle between the Medes and Lydians was brought to a close by a total eclipse of the sun, assumed to be that of 610 B. C. Now if it could bo ascertained by astronomical calculation that an eclipse was visible about that time in Asia Minor, its exact period would fix the date of the battle. But the calculation of a solar eclipse at such a remote time is a somewhat uncertain operation; for the minutest error in the tables used would throw the moon's shadow on an entirely different part of the globe. Mr. Airy, the British astronomer royal, has calculated that the eclipse of 610 could not have been visible in any part of Asia Minor, and that the only one applicable to the case is that of May 28, 585. If therefore the statement of the historian as to the fact, and the calculation of the astronomer as to the eclipse, are correct, the battle occurred in 585 and not in 610. Either may be erroneous, most likely Herodotus. Lunar eclipses, being visible over a whole hemisphere, require much less nicety of calculation, and are more available for chronological purposes. - The foundation of the modern science of chronology may be said to have been laid by Joseph Scaliger in his works De Emendatione Tem-porum (Paris, 1583; enlarged, Leyden, 1598; Geneva, 1629), and Thesaurus Temporum (Paris, 1000; best ed., Amsterdam, 1658). Among other important works are: Petavius, De Doctrina Temporum (Paris, 1027), with its continuation, Uranologion (Paris, 1030), and abridgment, Rationarium Temporum (Paris, 1630, and since); Riccioli, Chronologia Reformats (Bologna, 1669); L'Art de verifier les dates, by the Benedictines of St. Maur (last ed., 1783-'7), continued by Fortia d'Urban; Champollion-Figeac, Resume complet de chronologic generale et speciale (Paris, 1830); Ch. Dreyss, Chronologie universelle (1853); Kor-nick, System dcr Zeitrechnung in chronolo-gischcn Tabcllen (Berlin, 1825); Ideler, Hand-Jjuch dcr mathematischen und technischen Chronologie (Berlin, 1825), and Lehrbuch der Chronologie (Berlin, 1831); Matzka, Chronologie in ihrein ganzen Umfang (Vienna, 1844); Lepsius, Chronologie der Acgypter (Berlin, 1849); Archbishop Usher, Annales Veteris et Novi Testamcnti (London, 1650-,54); Sir Isaac Newton, "Chronology of Ancient Kingdoms" (London, 1728; an answer to it was written by Freret, Paris, 1758); Jackson, "Chronological Antiquities" (London, 1752); Blair, "Chronology and History of the World " (London, 1750; a new edition, revised and enlarged by J. W. Rosse, was published in London, 1850); Playfair, "System of Chronology " (Edinburgh, 1784); Hales, "New Analysis of Chronology" (1800-'12); Clinton, Fasti Hel-lenici (Oxford, 1824-'34), and Fasti Romani (Oxford, 1845-'50); Sir Harris-Nicolas, "The Chronology of History" (in Lardner's "Cabinet Cyclopaedia," vol. xliv., 1833). Rawlinson's translation of Herodotus (4 vols., London, 1858-'60; new ed., London, 1862, New York, 1872) is furnished with valuable dissertations in respect to ancient chronology by Sir Henry Rawlinson and Sir Gardner Wilkinson; and his "Five Great Monarchies" (2d ed., London, 1870; New York, 1871) treats elaborately of the chronology of Chaldea, Assyria, Babylon, Media, and Persia. Among the most useful manuals of reference are: J. W. Rosse, "Index of Hates" (London, 1858), which forms an alphabetical index to Blair's "Chronological Tables;" Haydn's "Dictionary of Dates," continued by Vincent (12th ed., London and New York, 1866, with supplement to 1870); Woodward and Cates's "Encyclopaedia of Chronology" (London, 1872).

* So in the Hebrew; in the Septuagint, 753.