<P> Neither the papal bull nor its attached canons explicitly fix such a date, though it is implied by two tables of saint's days, one labelled 1582 which ends on 31 December, and another for any full year that begins on 1 January . It also specifies its epact relative to 1 January, in contrast with the Julian calendar, which specified it relative to 22 March . The old date was derived from the Greek system: the earlier Supputatio Romana specified it relative to 1 January . </P> <Ol> <Li> Jump up ^ In 1793 France abandoned the Gregorian calendar in favour of the French Republican Calendar . This change was reverted in 1805 . </Li> </Ol> <Li> Jump up ^ In 1793 France abandoned the Gregorian calendar in favour of the French Republican Calendar . This change was reverted in 1805 . </Li> <P> During the period between 1582, when the first countries adopted the Gregorian calendar, and 1923, when the last European country adopted it, it was often necessary to indicate the date of some event in both the Julian calendar and in the Gregorian calendar, for example, "10 / 21 February 1750 / 51", where the dual year accounts for some countries already beginning their numbered year on 1 January while others were still using some other date . Even before 1582, the year sometimes had to be double dated because of the different beginnings of the year in various countries . Woolley, writing in his biography of John Dee (1527--1608 / 9), notes that immediately after 1582 English letter writers "customarily" used "two dates" on their letters, one OS and one NS . </P>

Who is responsible for naming the days of the week