dominical letter

Also called the Sunday letter. In the Calendar the first seven letters of the alphabet are applied to the days of the week, the letter A being always given to the first of January, whatever that day may be, and the others in succe ion to the following days. If the year consisted of 364 days, making an exact number of weeks, it is evident that no change would ever take place in these letters: thus, supposing the first of January to be Sunday, all the Sun days would be represented by A, not only in that year, but in all succeeding years. There being, however, 365 days, the letter A is repeated for the 31st of December, and consequently the Sunday letter for the following year will be G, and in the third year F. If every year were common, the proce would continue regularly, and a cycle of seven years would suffice to restore the same letters to the same days as before. But the intervention of a day in every bi extile or leap year occasions a variation in this respect. The bi extile year containing 366 days instead of 365, will throw the dominical letter of the following year back two letters; so that if the dominical letter at the beginning of any leap year be C, the dominical letter of the following year will be A, and not B. This alteration is not effected by dropping a letter altogether, but by changing the dominical letter at the end of February, where the intercalation of a day takes place. The following rule is given in the (English Church), Book of Common Prayer , to find the Dominical or Sunday letter according to the calendar in the Prayer-book: "For the next century, that is, from the year 1800 till the year 1899 inclusive, add to the current year its fourth part, and then divide by 7; if there is no remainder, then A is the Sunday letter; if any number remain eth, then the letter corresponding to that number is the Sunday letter."