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The 10 Hour Day

The metric system's biggest appeal is it's base unit of 10. 10's are just a whole lot easier to work with. For scientific measurements, 10's make it easy to calculate changes in orders of magnitude (that is, from millimeters to centimeters to kilometers instead of trying to do the math in feet or miles). Tens are just easier to manipulate. We have ten fingers and ten toes. We (in the US) use a base unit of 10 in our monetary system.

So why not make our days, hours, minutes and seconds into units of ten as well?

As it turns out, we almost did. The metric system, in a slightly less evolved state than what it is now, was adopted in France shortly after the French Revolution around 1789. The basis for the metric system had been around for about 200 years, but France's adoption snowballed into an almost world-wide change over to metric.

The Revolution lasted about ten years and saw the centuries old French monarchy toppled by civilian uprisings and replaced by a democratic system. Adopting metric was not only practical, it represented getting rid of the old regime and starting fresh. French leaders then decided to also make a calendar based on units of 10, and recruited mathematicians and scientists to help put it together (this included enlisting the help of Joseph-Louise Lagrange, whose name should be painfully familiar to calculus students).

The new calendar, known as the French Republican Calendar divided a year into twelve months (three for each of the four seasons), each made up of three 10-day weeks, with each day divided into 10 hours, divided into 100 minutes, divided into 100 seconds. So one of these new hours was actually about 144 minutes, or more than two traditional hours.

That didn't last long, for a number of reasons. I have my theory.

I'd have to argue that the calendar, measurements of time, are much more ingrained in our day to day lives than measurements of distance, length, mass, ect. Many people, including physicists, make up their own measurements to suit what they are measuring, or use comparison as often as exact measurements. For example, if I am trying to tell someone the distance between two locations, I often tell them a unit of time. It's 30 minutes away. What I mean is it's, assuming we are using the same method of transportation, this is how long it will take you to get there. That is often more valuable than distance. Have you ever used an object as a unit of comparison rather than an exact unit? Something was as big as a softball, a car, a house. Often times this is just easier than giving specific units of mass and size. Physicists have also come up with abbreviated measurements for values they use frequently. In the realm of the very large or the very small, traditional units (even with those handy units of 10) aren't always helpful. An Astronomical Unit is the distance from the Earth to the sun, and this is often better than giving the distance in millions of kilometers.

But this seems to be less often the case with time. There are units of time used in physics to refer to incredibly small or incredibly large lengths of time, but I would argue that these are used less often than in the case of other units. There is, for example, the Galactic Year, equal to 250 million years, but I don't hear this tossed around a lot. When talking about the universe, we still say that it is 13 or 14 billion years old (even though that time frame is difficult to grasp), but we measure its distance in light years, not kilometers, to make it easier to understand. The very smallest unit of time we have measured is the attosecond, or 10^-18 seconds. At that scale we are still using seconds, yet most chemists and physicists use angstroms when talking about measurements of length around 1x10^-10.

And of course that's not the only reason a new calendar would change things. It would mean the restructuring of some key elements of society, namely the work week. And there is also the religious pull - the Bible holds a seven day week, and in doing so keeps Sunday holy. Unless we wanted to continue to make a day of rest every seven days, which would make "Sunday" actually take place on various days during the week, we'd have to extend the week to ten days. Or, we could have shortened it to five, which would have been nice, but maybe not practical.

The calendar, though ultimately impractical because of how deeply entrenched the Gregorian calendar is in our lives, had some interesting aspects. In the way that the Christian calendar assigns some days to Saints, it assigned every day of the year with some thing. Days ending in 5 were assigned an animal. Days ending in 0 were assigned a tool, and all other days a plant or animal. Had this taken off we would have had The Day of the Cauliflower, The Day of the Blueberry, and The Day of the Marshmallow. You would also see these fun days: the potato, the vat (a tool?), the spinach, the corn salad, the hedge mustard, and the button mushroom. Today would be The Day of the Duck.

The French leaders also tried to divide a circle into 400 degrees, instead of 360 degrees. So instead of doing a 180 on someone, they would say you did a 200. Instead of 90 degrees to a right angle, there would be 100. The mathematician, physicist, sailor, and all around busy guy Jean Charles de Borda spent a lotta time building a new compass to go with the new system. But in the end it didn't stick. With a change like that to the foundation of geometry, you also have to change all of your logarithms and geometric functions like sine, cosine and tangent. As if that stuff isn't tricky enough as it is. And to be honest, dividing a circle into factors of 10 doesn't really make things much easier, since 100 isn't nicely divisible by thirds, which appear quite frequently in geometry. Still, for his good efforts Borda had a crater on the moon named after him, so it wasn't a total waste.

Happy Day of the Duck!


  1. The circle should really be 1000 degrees, so each quart section would be 250 degrees. It makes more sence than 360 degrees based on one day of earth movement around the sun, with actually is < one degree, by the way.

    And the ten hour day clock really does work well, no reason not to use it. Better that two of every number to 12, that is stupid and confusing. I will be there at 6:00. Is that 6 PM or 6 AM? No that is 7:50 Metric Time.


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