Much of the world sets store by the Gregorian calendar, instituted by Pope Gregory XIII in 1582. This new scheme, an adjustment to the ‘Julian’ calendar that had endured since the time of Caesar, corrected for a rounding error in the older system whose effects, by the sixteenth century, had begun to accumulate. (The spring equinox, meant to occur on March 21, was arriving ten days early, complicating the scheduling of Easter.) In much of Europe, Gregory’s new calendar caused the dates October 5–14, 1582 to vanish. But not everywhere.

Countries outside the Catholic sphere of influence attended this adjustment with less urgency. The Kingdom of Bohemia would take two years to make the change; Prussia would take twenty-eight. Spectacularly resistant to the change were the English, treating this bit of administrative bumf with their usual drollery, until finally succumbing in 1750. Their calendars for 1752 therefore skipped the dates September 3–13, at the end of a 170-year interregnum that had required the constant conversion between the calendar at home and abroad, giving rise to elaborate conversion scales such as these.

With obvious ecclesiastical, commercial, and legal applications, these alignment calendars calculated the difference between the dates in Catholic Europe and the various national holdouts. Their most complicated workings were devoted to the Swiss, whose various cantons, which during these years numbered between thirteen and twenty-six, gradually adopted the new calendar over a 227-year period. The disappearance of these contraptions from everyday use is a testament to the rational, well-coordinated, and widely-adopted systems in universal use today, in all things except the trade of commodities such as precious metals and real estate, and of course length, weight, and time.

Published December 13, 2023. Copyright © 2023 Jonathan Hoefler.