The Gregorian year, therefore (or the year in the Gregorian refor mation of the kalendar), is a portion of a cycle of 400 years of 365 days, 97 of which have an additional day. [KALE:sDAn.] The Julian year, in use before the Gregorian reformation, is a portion of a cycle of 4 years of 365 days, one of which has an additional day. With out a perfect comprehension of the manner in which the incom mensurability of the year and day is remedied, no progress can be made in the understanding of the nature and use of chronological periods.
An £ra means either the commencement of an indefinite reckoning, or of a succession of periods. In the article "Ems will be found the complete description of the most important mras; but as it often happens that fur reference the mere time of an obscure or uncommon rem is wanted without explanation, we subjoin an extensive het, merely giving the leading words, and the date A.D. or a.c. of the vulgar Christian wra. It is to be remembered that the births of Jesus Christ is supposed to have taken place in the fourth year a C. of this common term The figures following the years refer to months and days : thus A.D. 729 . 6 .13 would stand for • the 13th day of June, A.D. 729. We do not mean to say that the events in the following list did take place in the years, far less in the months, or on the days, which are set down : but only that those who used them as seem, took them as having happened in those years, months, and days. Thus the death of Alexander, according to Clinton, took place in me. 323, which is most likely to be right ; but if those who afterwards made an sera of this death, reckoned from the 12th of November B.C. 324, that day is the tern, whether the event happened then or not.
Among the various sources of confusion may be noticed-1, au old practice of astronomers, who call the year immediately preceding and following the vulgar sera, not 1 but 0, as calculation requires; 2, the discrepancies arising from different times of beginning the year. The most important of these to the English reader is the following : Before the change of style in 1752, and from the 14th century to that time, the legal and ecclesiastical year began on the 25th of March, though it was very common in writings, &c., to begin it on the lst of Hence January, February, and twenty-four days of March, were in one year, according to lawyers, &c.; and in another according to others. Thus the Revolution, so called, of 1688, took place in the February of that legal year, or, as we should now say, February, 1689. It is frequently written thus: February, 168:, or February, 1688-9.
Thus, King Charles was beheaded January 30, 164,1, or January 30, 1648-9.
We now come to the artificial periods which are of most use in chronological researches : these are 1. The cycle of the sun, or more properly the cycle of Sundays.
2. The cycle of the moon, or of nineteen years, or of the Golden number, or of the Primes, or the 3letonie cycle with its sera altered. [METON, in Moo. Div.] 3. The cycle of indictions.
4. The Paschal cycle.
5. The Julian period.
1. The cycle of the sun is a period of 2S years, compounded of 7 and 4, the number of days in a week, and the number of years in the interval of two leap-years. This, in the old style, makes the Sundays return to the same days of the year; every year of the cycle being in this respect exactly the same as the same year of the pre ceding cycle. Thus, the year A.D. 1 being the tenth in its solar cycle, and the DOIMCCAI. LETTER being for that year n, or the 2nd of January being Sunday, the 2nd of January was also Sunday in the year A.D. (1+ 28), or A.D. 29, also in A.D. (29+23), or A.D. 57, &o.
The series of dominical letters for the complete solar cycle is as follows : attached to each dominical letter is what is called the concurrent of the year, meaning the number of days elapsed over and above a complete number of weeks, from the beginning of the cycle (not including the first day) to that of the year in question, tho con current being written 7 where 0 would perhaps have been better.
The table given in DouralcAr. LETTER would save some of the following process, which however it is better to give.
Old Style.—To find the part of the solar cycle in which any given year is found. If the year be A.D., add 9 and divide by 28; the remainder (or 28 if the remainder be 0) is the year of the solar cycle required. But for a year n.c., deduct 10 from the date, and divide by 28 ; the remainder deducted from 23 gives the year. The dominical letter and concurrent are then taken from the preceding table. And to find on what day of the week the first day of any mouth fell, to the concurrent of the year add the regular of the month, the sum (dimi nished by 7, if it can be done) shows the day, 1 being Sunday, 2 Monday, &e. (But in leap-year one day later must be taken for every month after February.) Thus to find the day on which the sera of the hegira fell, or July 16, 622 A.D., 622+9 or 631 divided by 28 gives the remainder 15, which is the year of the cycle. The concurrent ie 4, which added to the regular of July 1, gives 5, or Thursday for the let July, and Friday for the 16th; whence Friday is the day required.