The year 1900 will not be counted among the leap years. The year is 365 days, five hours and forty-nine minutes long; eleven minutes are taken every year to make the year 365-1/4 days long, and every fourth year we have an extra day. This was Julius Caesar’s arrangement.
Where do those eleven minutes come from? They come from the future, and are paid by omitting a leap year every one hundred years.
But if leap year is omitted regularly every one hundredth year, in the course of four hundred years it is found that the eleven minutes taken each year will not only have been paid back, but a whole day will have been given up.
So Pope Gregory XIII, who improved on Caesar’s calendar In 1862, decreed that every centurial year divisible by four should be a leap year after all. So we borrow eleven minutes every year, more than paying our borrowings back by omitting three leap years in three centurial years, and square matters by having a lean year in the fourth centurial year.
Pope Gregory’s arrangement is so exact, and the borrowing and paying back balance so closely, that we borrow more than we pay back to the extent of one day in 3866 years.