DOMIN'ICAL LETTER, or SUNDAY One of the seven letters A. It C, D. E. F. G. used in calendar: to mark the Sundays throughout the tear. The first seven days of the year being marked in their order by the above letters in their order, then the following seven, and all tonsecutive sets of seven days to the end of the year, are similarly marked; so that the 1st, 8th, 13(11, •2(1, etc., days of the year are all marked by A; :mil the 2d, 9th, 16th. 2:3(1, etc.. by 1:; and so on. The days being thus marked, it is evident that on whatever day the first Sun day of the year falls, the letter which :narks it will mark all the other Sundays in the year, as the number of the letters and of the days in the week is the same.
As the common year consists of fifty-two weeks and one day over, the dominieal letters go back Ward one day every common year. if the do minival letter of a common year be will be the dominical letter for the next year, As a leap-year consists of lifty-two weeks and two days, the letter, go backward two days every leap year. if in the beginning of a leap-year the dominieal letter be O, 1.: will be the dominical letter fur the next year. This extraordinary re
tro•ession, however, is made to take place at the intereal I•y day I the 21)th of February) by the artifice of marking it by the same letter as the day it, and the next Sunday is marked by the letter preceding that which marked the Sundays before the intercala•y day. Suppose the 2sth of February in a leap-year to be a Sunday. and marked by 1', it is evident that the dominieal letter for the rest of the year will be E. As every fourth year is a leap-year. and the letters are `WWII in number, it is clear that the -ante order of letters must return in four time: seven, or twenty-ei7ht years, which woul but for the leap years, recur in seven years. and hence the solar cycle. (See Prnmn.) The do minical letters were first introduced into the calendar by the early Christians, to displace the nundinal letters in the Roman calendar. They are of Ilse as a means of on what day of the week day of t he HIOnth fall. hi a Oxen vial. ISee E 1Ni,-; and table: for finding. Ilion are given in prayer book, breviaries, eve., as well as in works on date,