Calendrical Calculations

A correspondent writes to the Virtual Stoa:

Just a tiny point about the French republican calendar: your converter is a day out at the moment (presumably it’s using a different leap year rule).

Thanks for this: you’re right that the Calendar installed at the top of this page is a little different from the one over at the site you link to, and right to guess that it has something to do with where the leap years come in.The page that you linked to presents the astrological version of the Calendar, which was the one that the French actually used for about a decade; the Calendar on this page is based on the 1795 amendment proposed by the Montagnard Gilbert Romme (and, I think, approved but never implemented), which aimed to regularise the pattern of leap years and — crucially — to forgo the need to calculate the precise date of the equinox each year.

On this mathematical model, every fourth year was to be a leap year, except every hundredth year, which was not to be a leap year, except for every four hundredth year, which was to be a leap year; and in addition to all of this (which is, so far, along the lines of the Gregorian Calendar), a three-day correction was called for every four thousand years, and each of these four thousand-year cycles was to be known as a “franciade millaire”. And that’s where the radical improvement over the Gregorian Calendar, over the very long haul, comes in.

The bit of script which generated this calendar was originally written by my friend Steve to turn Star Trek Stardates into and out of Gregorian dates, and he did the conversion job himself to turn the code into an altogether more progressive Revolutionary Calendar Generator. I’m forever in his debt.

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