BISSEXTILE

, or Leap-year, a year consisting of 366 days, and happening every 4th year, by the addition of a day in the month of February, which that year consists of 29 days. And this is done to recover the 6 hours which the sun takes up nearly in his course, more than the 365 days commonly allowed for it in other years.

The day thus added was by Julius Cæsar appointed to be the day before the 24th of February, which among the Romans was the 6th of the calends, and which on this occasion was reckoned twice; whence it was called the bissextile.

By the statute De anno bissextile, 21 Hen. III, to prevent misunderstandings, the intercalary day and that next before it are to be accounted as one day.

To find what year of the period any given year is; divide the given year by 4; then if o remains, it is leap year; but if any thing remain, the given year is so many after leap year.

But the astronomers concerned in reforming the calendar in 1582, by order of pope Gregory XIII, observing that in 4 years the bissextile added 44 minutes more than the sun spent in returning to the same point of the ecliptic; and computing that in 133 years these fupernumerary minutes would form a day; to prevent any changes being thus insensibly introduced into the seasons, directed, that in the course of 400 years there should be three sextiles retrenched; so that every centesimal year, which is a leap year according to the Julian account, is a common year in the Gregorian account, unless the number of centuries can be divided by 4 without a remainder. So 1600 and 2000 are bissextile; but 1700, 1800, and 1900 are common years.

The Gregorian computation has been received in most foreign countries ever since the reformation of the calendar in 1582; excepting some northern countries, as sussia, &c. And by act of parliament, passed in 1751, it commenced in all the dominions under the crown of Great Britain in the year following; it being ordered by that act that the natural day next following the 2d of September, should be accounted the 14th; omitting the intermediate 11 days of the common calendar. The supernumerary day, in leap years, being added at the end of the month February, and called the 29th of that month.