How the Quest for a Perfectly Rational Calendar Created a 13th Month

By Roman Mars on at

A month is hardly a unit of measurement. It can start on any day of the week and last anywhere from 28 to 31 days. Sometimes a month is four weeks long, sometimes five, sometimes six. You have to buy a new calendar with new dates every single year. It’s a strange design.

The calendar that the world uses right now is mostly a combination of the Roman lunar calendar and the Egyptian solar calendar, a product of the love affair between Caesar and Cleopatra. She was 21 and he was 52, and when they got together, they did what lovers do: discuss the true nature of the earth’s rotation.

The Egyptians had already discovered that the year is roughly 365 days long because of the Nile river. Egyptians had “Nilometers,” structures that went into the Nile that could predict the seasons, thanks to the Nile’s tendency to flood to the same height at virtually the same day every year.

How the Quest for a Perfectly Rational Calendar Created a 13th Month

[A Nilometer on Rhoda Island, Cairo. Credit: Baldiri]

The Egyptians also figured out that the year isn’t always exactly 365 days, so they added an extra day every four years, just to make sure the calendar year matched up with the seasons. In other words, they invented the leap year.

This was all fantastic news to Caesar, because he had a feeling that the Roman calendar wasn’t quite right. At that time, the Roman calendar year, which was based on the phases of the Moon, was only 354 days long.

How the Quest for a Perfectly Rational Calendar Created a 13th Month

[A Roman calendar before the Julian reform]

The Julian calendar, which added the eleven missing days and put a leap day in February, was instituted throughout the Roman empire. Still, the Julian calendar was about 11 minutes and 14 seconds off each year. These minutes added up to lost days and then an entire lost week.

By 1582, Pope Gregory finally realised that everyone was worshipping all the holy days on the wrong dates from what they originally were. He made a few adjustments to realign the year with the seasons (including loosing ten days), and created the Gregorian calendar, which is what’s on your wall or your phone.

How the Quest for a Perfectly Rational Calendar Created a 13th Month

[Courtesy of the George Eastman House]

Now we basically live with the Gregorian calendar and don’t question it. However, throughout history there have been a number of attempts to redesign the calendar.

One calendar re-design came after the French Revolution; revolutionaries decreed the first year of the revolution was the year 1, and they made the week ten days long. This calendar endured for more than a decade, lasting until Napoleon crowned himself emperor.

In 1849, another Frenchman, August Comte, created the so-called Positivist calendar, which reorganised the months and renamed them after great men of history (Moses, Homer, Aristotle, etc.).

The positivist calendar didn’t take off. But there was another radical attempt at calendar reform that did.

How the Quest for a Perfectly Rational Calendar Created a 13th Month

[Courtesy of the George Eastman House]

Moses B. Cotsworth worked the books books for the British railway, and the wonky, weirdly-divided Gregorian Calendar was making his job difficult. In 1902, Cotsworth presented a design for a calendar of 13 months where every month was exactly 28 days. No more, no less. Four perfect weeks.

This meant the dates were all standardised as well. Regardless of the month, the 5th was a Thursday. The 1st was always a Sunday. The 10th was always a Tuesday. There would be a Friday the 13th every single month—clearly, rational railway men were not superstitious.

All the month names would stay the same and an additional 28-day month would fall between June and July. This additional month would be called “Sol,” standing for the month when the summer solstice occurs. Leap Day would be added to the end of Sol, not February, so every four years, Sol would have 29 Days.

How the Quest for a Perfectly Rational Calendar Created a 13th Month

[Courtesy of the International Institute of Social History]

13 months of 28 days makes for 364 days in a year. To make it 365, Cotsworth added a new holiday after December 28—”Year Day,” a floating day, not part of any month. It would be a global sabbath.

How the Quest for a Perfectly Rational Calendar Created a 13th Month

[Courtesy of the International Institute of Social History]

Aside from year day, all other vacations would be moved to a Monday. All holidays would be three day weekends.

Cotsworth toured the United States giving talks about his calendar’s myriad benefits, but he couldn’t find many takers. Though he did attract the interest of one of the wealthiest and most successful men of that time: George Eastman, the founder of Kodak.

Eastman took it upon himself to promote Cotsworth’s calendar design. He started a calendar league headquarters in Rochester, in Kodak’s office. There they published and printed different flyers to hand out to local businesses and actually convinced a few local business to switch to a 13 month calendar. Including, of course, Mr. Eastman’s own company, Kodak.

How the Quest for a Perfectly Rational Calendar Created a 13th Month

[Courtesy of George Eastman House]

The Eastman Kodak company adopted the 13 month calendar in 1924 and they continued to use it until 1989. The 13 month calendar was in use for 65 years.

However, within Kodak, Eastman couldn’t fully institute the 13 month calendar in its truest form. Kodak employees didn’t observe “Sol” or “Year Day” or change every holiday to a Monday. They used it like how some bankers work in quarters or some schools function in semesters- Kodak’s internal schedule was organised into 13 “periods”, labelled period 1 to period 13. They used the 13 month calendar as an organisational tool for planning finances and production schedules, but employees still lived their lives on the Gregorian calendar.

How the Quest for a Perfectly Rational Calendar Created a 13th Month

[Courtesy of the International Institute of Social History]

George Eastman knew that if he wanted to truly standardise the calendar, Kodak couldn’t do it alone. He would have to convince the rest of the world to make the switch. Eastman and Cotsworth presented the calendar to various committees in the U.S. Congress, and calendar reform became an actual issue of debate for the League of Nations, the precursor to the U.N. At one point The League of Nations was considering 185 different calendar redesigns, and Cotsworth and Eastman’s proposal was one of a few finalists.

Even after Eastman passed away in 1932, the League of Nations continued discussing calendar redesign, but they couldn’t come to a consensus. And then, Hitler and World War II made the project of redesigning the calendar thoroughly unimportant. And then, the League of Nations folded.

We haven’t really considered calendar reform since. But there’s no reason we can’t take our vacations in Sol and celebrate Year Day.

How the Quest for a Perfectly Rational Calendar Created a 13th Month

[Courtesy of the International Institute of Social History]

Producer Avery Trufelman spoke with David Ewing Duncan, author of Calendar; Mark Byrnes, who wrote about the 13 month calendar for CityLab; Kathy Connor of George Eastman House; and longtime Kodak employees John Cirocco and Robert Shanebrook (who is also the author of Making Kodak Film).


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This post has been republished with permission from Roman Mars. It was originally published on 99% Invisible’s blog, which accompanies each podcast.

Featured image: DafneCholet/Flickr