CHRONOLOGY, HISTORY or. Chro nology, as regards the natural divisions of time, was doubtless coeval with the creation, for we learn from the sacred historian that the work of creation was performed within the period of a week, or seven days, whence this division was observed by the Hebrews, and from them transmitted to the Egyptians and other nations. But the Persians are said to have been ignorant of such a division. The Greeks had weeks of ten days, and the Romans weeks of eight days. It is evident from the names of the days of the week among mostEuropean nations, that we derive this division from the ancient Celts or Scy thians, who, in all probability, at the disper sion of mankind after the deluge, borrowed this patriarchal mode of measuring time. The year is that division of time which was regulated by the motions of the sun, being that period of time in which the sun passes through the signs of the zodiac. This divi sion was doubtless formed at the time that astronomical observations were first made ; but the Egyptians are the first people on record who formed this division, which they made to consist of 360 days, and sub divided into 12 months of 30 days each; to these Trismegistea is said to have added five more days. The ancient Jewish year was the same as the Egyptian ; but on their de parture from Egypt they adopted the lunar year, consisting of 30 days and 29 days alternately, and in order to make it agree with the solar year, they sometimes added 1 1 or 12 days at the end of the year, and ,sometimes a whole month after a certain 'number of years. The Greeks also reckon ed by the same kind of year. The ancient 1Roman year was also lunar, and at first con slated of 10 months of 30 and 31 days ; two months were afterwards added by Num Porupilius, which consisted of 29 and 31 days, making in the whole 355 days. Julius Caisar first reformed the calendar, and adopted the solar year of 365 days in the common year, with the- addition of a day in every fourth _year, called Bissextile, or Leap Year ; in order to adjust the computation to the true solar year, it was then reckoned 365 days 6 hours, but as the true solar year was found to be 365 days, 5 hours, 48 minutes, 46 seconds, a farther reformation of this calendar has been made, on the assumption that the solar year consists of 365 days, 5 hours, and 49 minutes. According to this computation, which was made by Pope Gregory XIII. in 1582, and thence called the Gregorian style, an intercalation of one day in February should be made every fourth year, and that the sixteen hundredth year of the Christian era, and every fourth century hereafter, should be a bissextile or leap year. One day consequently is to be intercalated in the years 2000, 2400, 2800; ; but in the intervening centuries 1700, 1800, 1900, 2100, fie. itis to besuppressed, and they are to be reckoned common. More over, as the equinoxes had fallen back ten days, and the full moons four days, since the Nicene council, A. D. 325, he ordained that ten days should be cut off after the fourth of October, so that the fifth should be the fif teenth. This mode of reckoning, which is now introduced in most countries of Europe, is called the New Style, to distinguish it from the Old Style, or the former reckoning. This is however still not perfectly correct, for as the excess of the Julian year, within the space of four centuries, is three days, one hour, and twenty minutes, that of the Gre gorian is one hour and twenty minutes with in the same period, or about a day in 7200 years.
Besides these alterations in the form and length of the year, attempts had been made by the Greeks at an early period to adjust in their reckonings the lunar year to the solar year, for which purpose they hit on the device of framing cycles or series of years, which being numbered in an orderly man ner from first to last, should return to the same point of reckoning from which they commenced. The first of these cycles was
framed by Cleostratus, about 532 years be fore Christ. It consisted of eight years, or 2922 days, during the coarse of which 96 Inflations would elapse of 29 and 30 days al ternately, together with three intercalary months. By this cycle he proposed to adjust the lunar to the solar year, so that at the conclusion of each cycle the moon should be renewed, but he failed in his object, for at the end of 16 years there was forma to be an error of three days, which in the space of 160 years would amount to more than a whole month. The Metonic Cycle, formed by !!felon at the commencement of the Pelopon nesian war, for the purpose of correcting the former, consisted of 19 years, at the end of which the sun and moon would be in the same quarter. This cycle, which was an much esteemed by the Greeks as to be called the Golden Number, nevertheless failed to the amount of eight- or ten hours at the end of one period, and of three days in 133 years. The cycle of Ender= was en im provement on that of Cleostratus, by sub tracting a month of 30 days from a period of 160 years, which was supposed to be equal to the difference that would subsist at the expiration of that period between the solar and the lunar motions. The Calippie Period, contrived by Calippus at the new moon of the summer B. c. 331, was intended as an improvement upon that of 31elin, which it multiplied by four, so as to make a period of 76 years, or 27,759 days. As 940 luna dons are equal to 97,758 days, 9 hours, 5 minutes, and 9 seconds, which is only lees than 76 solar tropical years, it fol lows that the lunar motion, according to this calculation, did not vary more than 14 hours, 13 minutes, and 22 seconds, wherefore this period has been chosen to form the basis to the modern cycle of the moon, which is said to have commenced one year before the Christian era. There is also a solar cycle, consisting of a series of 28 years, at the com pletion of which the same order of bissextile and dominical letters return, a cycle which came into use in the early ages of Christian ity ; besides the cycle of indiction, or a series of 15 years, introduced in the reign of Con stantine; the Epacts, or excesaes of any solar revolutions above the lunar, which were introduced for the purpose of ascertain ing the time when Easter ought to be cele brated ; the Dionysian Period, or series of 532 years, formed by Dionysius Exiguus, a Roman abbot, by multiplying the solar cycle 28 into the lunar 19, for the purpose of res toring the new and full moons to the same day; and lastly, the Julian Period, invented by Scaliger, and so called because it is adapted to the Julian year ; this is a series of years formed by the multiplication of the solar and lunar cycles and the cycle of indiction into one another, making the sum of 7980 Julian years.
The application of chronology to history is of comparatively modern date. In Homer and other ancient writers there appears to have been no idea of recording events in any exact order of time. The succession of Jnno's priestesses at Argoe served Hellanicus for the regulation of his history, but the principal Greek historians followed no other order than what was furnished by the aeries of events which they narrated. The Roman historian Livy defines the periods of the events de scribed in his history by the appointment of consuls, and afterwards the succession of em perors and kings served a similar purpose in forming the histories of other European na tions, until a more exact computation of time began to be observed.