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Calendar (Gregorian). The reformed Julian Calendar introduced by the Bull of Pope Gregory XIII., in February 1582, and adopted in England in September, 1752. By the "new style" of distributing and naming time the length of the year of the Gregorian Calendar is regulated by the Gregorian rule of intercalation, which is that every year whose number is the common reckoning, since the birth of Christ, is not divisible by 4, as well as every year whose number is divisible by 100, but not by 400, shall have 365 days, and that all other years, namely, those whose numbers are divisible by 400, and those divisible by 4, and not by 100, shall have 366 days. The Gregorian year, or the mean length of the years of the Gregorian Calendar, is 365 days, 5 hours, 49 minutes, and 12 seconds, and is too long by 26 seconds. The Gregorian rule has sometimes been stated as if the year 4000 and its multiples were to be common years: this, however, is not the rule enunciated by Pope Gregory. The Gregorian Calendar also regulates the time of Easter, upon which that of the other movable feasts of the Church depend. See EASTER.