Why did the 1878 calendar repeat itself four times in the 20 years between 1888 and 1908?

Answer 1

That is just the way the calendars do repeat. A calendar repeats either every 5, 6 or 11 years, or every 28 years in the case of a leap year. A leap year skips a day, so you don't wait 7 years for a day to come round a second time. Depending how the leap years lie in relation to a year, one day may be skipped in a 7 year period, 2 days may be skipped in a 7 year period, if there are 2 leap years in that period, or the day you are expecting to come round is itself skipped, which accounts for an 11 year gap. If you check a set of calendars for that period, or any period you will see how the gaps are normally 5, 6 or 11 years.

1878 started on a Tuesday. As part of the normal pattern, there was an 11 year gap to 1889. 1884 did start on a Tuesday but being a leap year, it had 29 days in February, which 1878 did not, so it was not a repeat of 1878. So 1889 was the next normal year to start on a Tuesday. There was then a 6 year gap to 1895, as 1892 was the only leap year in that period, causing 1 day to be skipped. 1900 was not a leap year, which slightly disrupted the normal pattern of a leap year being every 4 years. It would normally have been a 5 year gap after that, but because 1900 was not a leap year, there was another 6 year gap to 1901, as 1896 was the only leap year in that period. Then there was a 6 year gap to 1907 as 1904 was the only leap year in that period. So that is how the 4 years occurred.