The calendar which was brought into use by Julius Cæsar, and was carried all over the then known world by the Romans, aimed to measure the year by the time it takes the earth to move once around the sun. His Egyptian astronomer figured that this required 365¼ days, so the practice was begun of having three years of 365 days, followed by a leap year, to which an extra day is given. As a matter of fact, the length of the average year is _not exactly_ 365¼ days. To be sure, that is only 11¼ seconds or so out of the way, and this may seem a very small matter out of a whole year; but what happens is that every 128 years or so the calendar of Julius Cæsar or the Julian Calendar, as it is called, gets a day behind. By the year 1582, when Gregory XIII was Pope, the calendar was ten days slow. So Pope Gregory issued an order that the year was to take a new start and that thereafter three leap years out of every four centuries should be omitted, which keeps the calendar very nearly correct. But though Pope Gregory might decree, it did not follow that every one would obey at once; the ignorant thought that by the change of date they were losing ten days of time and, of course, of wages. After some confusion all the Roman Catholic countries obeyed. England, being a Protestant country, ignored Pope Gregory’s commands. But it could not so easily dismiss the knowledge of its own astronomers that the Gregorian Calendar, as it is called, is nearer the truth than the Julian. In 1752, therefore, the date of the day of the year was changed by an Act of Parliament. The day after September 3 was to be called September 14, which it would have been if the calendar had not been slow. And naturally the change was also made in America, to which the new style had been brought already by French and Spanish settlers from Catholic countries. There were always hot jealousies between the Eastern Church, ruled from Constantinople, and the Western, ruled from Rome. The Eastern or Greek churches refused to change their calendar on the order of a Latin Pope, and to this day retain the old style, the Julian dates. This is why their Christmas follows our Twelfth Day, for by this time their calendar is thirteen days behind the Gregorian. But to avoid confusion the double date is very generally in use.