The reckoning of time among the ancients was very inaccurate. This was
owning to their ignorance of astronomy, and also to changes that were
made from time to time for political reasons. The calendar was reformed
by Julius Cæsar, 46 B. C., who made the year consist of 365-1/4 days,
adding one day every fourth year. In 1582, the error in the calendar
established by him had increased to 10 days; that is, too much time had
been reckoned as a year, until the civil year was 10 days behind the
solar year. To correct this error, Pope Gregory XIII. decreed that 10
days should be stricken from the calendar, that the day following the 3d
day of October, 1582, should be made the 14th, and that henceforth only
those centennial years should be leap years which are divisible by 400.
Most Catholic countries adopted the Gregorian Calendar soon after it was
established. Great Britain did not adopt it until 1752, when the error
amounted to 11 days. By Act of Parliament, the 3d of September was
called the 14th. The civil year by the same act was made to commence on
the 1st of January, instead of the 25th of March, as was previously the
case.
[Illustration: THE COMPARATIVE TIME ZONES OF THE WORLD]
Dates reckoned by the Julian calendar are called Old Style (O.S.), and
those reckoned by the Gregorian calendar are called New Style (N.S.).
The difference now amounts to 12 days.