But few nations among the moderns, and we know of none among the ancients, except the Greeks and Romans, that had any acquaintance with this sort of history. A fact which may be attributed,--1st. To the government; for the more completely the affairs of a nation are under the control of arbitrary power and caprice, whether of one or more individuals, so much the less apparent is a rational internal connection of events. Hence philosophical history flourishes most under free governments; and has not even a shadow of existence under pure despotic constitutions. 2nd. To the degree of civilization to which the nation may have attained: for the observing and unravelling of the political connection of events presupposes a considerable progress in philosophical culture. 12. Since all events are considered in reference to the time and place in which they occur, it follows that geography and chronology are indispensable as auxiliary sciences in the study of history, especially the ancient. These sciences, however, need not, for this purpose, be considered in their full extent and detail, but only so far as they are of use in determining and arranging events according to time and place. A fixed mode of computing time is therefore necessary in ancient history, as well as a continuous geographical description of the countries which were the theatres of the principal events. 13. No method of computing time was adopted generally in antiquity. Each nation, each state, had its own era: yet, in the explication of ancient history, there is an evident necessity that some common era should be fixed upon, by which a synchronistic view of the various events may be obtained. For this purpose, the years may be computed either from the creation of the world, or before and after Christ. The latter method has the advantage not only of greater certainty, but also of greater convenience. Of the various modes of computing time, the best known are those of the Greeks and the Romans; the former by olympiads, the latter by years from the foundation of Rome. The era of the olympiads commences at B. C. 776; that of the foundation of Rome commences at B. C. 753, according to Varro; at B. C. 752, according to Cato.--The era of the Seleucidae, in the Syrian empire, commences with B. C. 312.--Various other eras, such as that of Nabonnassar, commencing with B. C. 747, are founded on observations preserved by Ptolemy, and made known by SCALIGER, in his _Doctrina Temporum_. Chronology constitutes a distinct science: the best introduction to which will be found in: # J. C. GATTERER, _Epitome of Chronology_. Gottingen, 1777. A most excellent criticism on the ancient eras has lately been communicated to the public by: # L. IDELER, _Historic Researches into the Astronomical Observations of the Ancients_. Berlin, 1806. # D. H. HEGEWISCH, _Introduction to Historical Chronology_; 1811. A very useful and portable work.