The Jewish Calendar dates all the years downwards from the creation, which it reckons at 3760 years and 2 months before the Christian era. The civil year begins with the month Tisri, the ecclesiastical with the month Nisan.

The Mohammedan Calendar begins with the first day of the first month of the year in which the Hegira, or flight of Mohammed, took place, i. e. 622 A. D., and was instituted in 639 or 640.

The year of this calendar is shorter than ours by 10 days, 21 hours and 14| seconds.

The Julian Calendar, that adjusted by Julius Caesar, made the year to consist of 365 days 6 hours, the fourth year containing 366 days; this was superseded by that of the Gregorian Calendar (New Style), so called from its having been authorized by Pope Gregory XIII. That pontiff, to harmonize the civil with the solar year, the former being in arrear, charged the Council of Trent with the correction of the Julian Calendar, and in 1582 issued a. new calendar, omitting ten days, October 5 becoming October 15. All the nations of Europe, excepting Turkey, Greece and Russia, have adopted it. The New Style came into force in Great Britain in 1751; September 3 becoming September 14 in 1752.

In 1793 the National Convention of the first French republic decreed that the common era should be abolished in all civil affairs, and that a new era should commence from the foundation of the republic, September 22, 1792. The year was to be divided into twelve months of thirty days each, with five complementary days at the end, which were to be celebrated as festivals, and were dedicated to Virtue, Genius, Labor, Opinion, Rewards. Every fourth or "Olympic" year was to have a sixth complementary day to be called "Revolution Day," and every period of four years was to be called a Franciade. The first, second and third centurial years - viz. 100, 200, 300 were to be common years, the fourth centurial year 400 was to be a leap year, and this was to continue till the fortieth centurial year 4000, which was to be a common year. The months were to be divided into three parts of ten days each, called decades. The names of the months and the days of the Gregorgian Calendar to which they corresponded are given in another section.