The Spanish zra, founded on a division of the Roman provinces among the Tri umviri, was long in use in Spain and Af rica, and was adopted in the dates of the principal councils and synods held in those countries. It is reckoned from the first of January B. C. 38. This was afterwards superseded by The Christian xra. Learned men have differed in opinion with respect to the exact time of the birth of Christ, some placing it four, others seven, years earlier than the first year of the Christian mra.
The uncertainty which exists upon this point arises from the zra not having been used until so many centuries had elapsed, that it was impossible to fix the date with accuracy. This is, however, of very little consequence in the application of this zra to chronological purposes, for all are agreed as to the numerical date of every year, the year 1808, for instance, being universally received as the year 1808 of the Christian zra, although probably not the exact measure of the time which nas elapsed from the birth of Christ. This zra was invented about the year 527 by I)ionysius, a Roman abbot, who reckon ed the first year of it to correspond with the 4714th of the Julian period. It may be useful to give the reader a view of the years of the other principal xras which correspond to the first of this : according to Playfair, (who, it is to be observed, differs in many respects from other chro nologers, but is, nevertheless, a most re spectable authority) these are the 4008th year of the world, the first year of the 195th Olympiad, the 754th year of Rome, the 749th of the Nabonassarean xra, the 313th of the Seleucidx, the 46th Julian year, and the 39th of the Spanish zra.
The zra of Dioclesian was used pretty generally by the Christians previous to the invention of the Christian xra. It is dated from the year A. D. 284, and probably took its rise from the persecu tion under that Emperor, although its date is computed from the first year of his reign.
The Hegira, which may be called the Mohammedan xra, is founded upon the flight of Mohammed from Mecca to Me dina, to escape the persecution of his ene mies, and is computed by his followers from A. D. 622. The beginning of their year is however made to correspond with the 16th day of July. In comparing any year of this xra, therefore, with the cor responding year of the Christian zra, it will be necessary to bear this in mind be fore it can be done with accuracy. The same may also be observed with regard to some of the other zras, the beginnings of the years of which do not exactly cor respond with that of the Julian year.
The Persian zra, or the zra of Yezde jerd, is the last we shall notice. Yezdejerd was the last of the Persian monarchs who was subdued by the Saracens. Accord ing to the opinion of the most reputable modern chronologers, this zra commenc ed in June, A. D. 632, corresponding with the beginning of the eleventh year of the Hegira. and with the first year of the reign of Yezdejerd . The years of this mra, like the Nabonassarean, consists of 12 months of 30 days, with an addition of 5 intercalary days at the end, making in all 365 days.
The limits of our plan will not allow us to enter more minutely into the details of this important science. For these we must refer to separate treatises on the subject. The abstract which is here given will, however, be found sufficient for all the general purposes of the histo rical student. We have purposely re frained from giving a chronological table of remarkable events, as such tables are to be procured with very little trouble. Various ingenious methods have been in vented, of associating the name of some remarkable event with the date of its oc currence, with the view of impressing it on the memory ; for some account of these, we must refer to the article ME MORY ARTIFICIAL.