CHRONOLOGY (Fr. chrwtoloyie, from Lat. chrono/ogia. from (.;k. xpovoXoyla, eh run o/ogia, from xp6vos, chronos, time + X6-yos, logos, ac count). The branch of science which treats of time as measured, computed. and recorded. Its object is to establish some method of defining time, to compute the intervals between important historical events. and to fix the dates of events uniformly with reference to some chosen point in the history of the world.
The familiar units of time are the year, the month, and the day. These are astronomical, and are determined by reeurring celestial phenomena. The epoch universally employed to day, before which and after which events are said to have occurred, is the birth of Christ. The years before Christ are marked 'Lc, and those after .k.D. (Arno Domini). The astronom ical units, however. have not always been em ployed, and the epoch or reckoning point differed among various peoples. Thus in early days. such vague periods as generations. or reigns of kings. were assumed as units; but finally, through the suggestion, it is said, of the philosopher Era tosthenes. \vim wa• in charge of the library in Alexandria, in the Third Century n.c., the year was introduced as the unit of time. The differ ence in epochs led to various suggestions which were gradually discarded with the spread of civilization and the closer intercourse of men. The systems used by the Greeks and Romans were most important in antiquity. The Greeks calculated by Olympiads, beginning their era from the years of the victory of Corodnis in the Olympic games. corresponds to the year me. 776. The 'loin:ins began their era from tlie founding of the city, generally accepted as the year n.c. 753.
The study of the astronomical units and the measurement of tint( belong to the department of mathematical astronomy. The historian em ploys chronology to enable hint to transfer events in history located in time according to various eras to his own system. the Christian Era.
The method of reckoning time by Olympiads was used by the historian Timams about n.c. 240, and was generally adopted by other Greek his torians. The olympiads were determined by the
olynipie games. which were livid every four years in the summer-time. The Olympic year there fore begins in the middle of our year, and the first and latter half of our year to differ ent Olympiads, Socrates was put to death in the first year of the 05th Olympiad. The reckoning is as follows: 91 X 4 = 376; this sub tracted from 776 gives 400, but his death took place in the eleventh month, hence I should be subtracted. so that n.c. 309 is the year of his death with reference to the Christian Era. if the date falls after Christ, 776 must he sub tracted from the Olympic year. The calculation by Olympiads lasted down to the Fifth Century of our era.
The date of the foundation of Route is given by Fabius l'ietor in a year corresponding to n.c. 747, by Polybius in Wu. 750. by M. Porcius Cato in tt.c. 751, by Verrins Haccus in WC. 752, and by Terentius Varro in It.c. 753. Among Pannan writers Livy follows Cato and at times Fabius Pictor. ('hero and Pliny follow Varro. The Varronian date is generally accepted by mod ern writers. In changing front the Homan to the Christian Era, subtract the year: of Itoine from 754 if the. date is before Christ, but if the date after Christ subtract 754 from the year of The Greek and Roman methods continued in use long after ('heist. Constantine the I :rent is said to have introduced the system known as indiction. This was a cycle of fifteen years whiel‘ were denoted Indiction 1, Indiction 2, lip to In diction IS. when the series began anew. There are four kinds of indi•tions. which owe their dif ference merely to the tact that they are reckoned from di trerent Thus the Indiction of ('on stantinople began with September 1, A.D. 312: the Imperial. on September 21, A.D. 312; the Homan or Pontifical, on December 25, A.n. or January I. A.n. 313; that of the Parliament of Paris. in October. As A.n. 1 equals Indiction 4. add 3 to the year of the Christian Era and divide by 15, and the remainder will be the num ber of the Indiction. If there is no remainder the Indiction is 15.