CHRONOLOGY, is that science which relates to time; treats of the division of it into certain portions, as days, months, years, centuries ; and the application of these portions, under various forms and combinations, as cycles, xras, &c. to the elucidation of history. What is proposed in the present article is, to point out the chief methods by which the several por tions of time have been computed, and in which they have been employed in as certaining the connection, and determin ing the dates, of past transactions.
The divisions of time which most pro bably first attracted the notice of man- . kind, as most obvious to their senses, were those marked by the revolutions of the heavenly bodies, days, lunar months, and years: and if these had correspond ed so exactly to each other, that every lunation had consisted uniformly of the same number of days, and each year of a regular number of complete lunations, the business of chronology would have been attended with comparatively little difficulty. In consequence, however, of variations in the revolutions of the earth, which it is not requisite here to explain it has become necessary to adjust these periods to each other by certain artificial divisions. Of these divisions, Tlu, Bay claims our first notice. In common speech, a day means that period of time, which is included between the first appearance of light in the morning and the return of darkness in the evening, or during which the sun is visible above the horizon. But the word is used, in a more comprehensive sense, to denote the time of a complete revolution of the earth round its axis. The former has been denominated a natural, the latter a civil, and sometimes a solar, day. The beginning of the day has been variously reckoned by different nations. The Chat dxans, Syrians, Persians, and Indians, reckoned the day to commence at sun rise. The Jews, also, used this method for their civil, but began the sacred day at sunset: this latter mode was used likewise by the Athenians, the Arabs, the Ancient Gauls, and some other Euro pean nations. The Egyptians appear to
lime had several methods of reckoning their day; probably the mode varied in different parts of the country, and in the same place at different periods. The an cient inhabitants of Italy computed the day from midnight, and in this they have been followed by the English, French, Dutch, Germans, Spaniards, and Portu guese; modern astronomers, after the Arabians, count the day from noon.
The day was subdivided by the Jews and Romans into four parts, which they denominated watches or vigils; the first commenced at six in the morning, the at nine, the third at twelve, and the fourth at three in the afternoon. The beginning of the first watch was, by the Jews, called the third hour, and so on in succession to the fourth watch, which was the twelfth hour. The night was divided in a similar manner. Other modes of dividing the day have been in use among different nations; but that which is now most general in civi lized countries is into 24 equal parts or hours. With respect to the different inventions which have been used for mea suring or distinguishing the hours of the day, we refer to the articles CLsrsynna, CLOCK, SUN-DIAL, &C.
The Week, is a division of time, ofwhich it may be proper to take some notice be fore we proceed to the month. Various divisions which might be included under this denomination have obtained in dif ferent countries. The earlier Greeks divided their month ikto three portions; of ten days each : the Northern Chinese had a week of fifteen days, add the Mexi cans one of thirteen. But the Chaldeans, and most other Oriental nations, have, from time immemorial, used the Jewish week of seven days, which has been adopted by the Mahommedans, and in troduced, with christianity, to most of the civilized nations of the world. ,In the Old Testament, the term week is oc casionally applied to a period of seven years, as well as of seven days; and to this it is necessary to attend, in order to understand the passages wherein the word is used in that sense.