Metric Time

There are 24 hours in a day, seven days in a week, and (roughly) 365 days in a year. There are 60 minutes in an hour and 60 seconds in a minute. You probably knew all that. But you know it because you’ve committed it to memory — it’s not something you can reason out. It’s not entirely clear why our days have two 12-hour halves or why our hours have 60 minutes of 60 seconds each.  Scientific America (March 5, 2007) claims the ancient Egyptians are the originators of the 24-hour day — “the importance of the number 12 is typically attributed either to the fact that it equals the number of lunar cycles in a year or the number of finger joints on each hand (three in each of the four fingers, excluding the thumb), making it possible to count to 12 with the thumb.” Or maybe it’s the ancient Babylonians, who, for some reason, used a base 60 system. (And note, 60 is just 12 times five.) But neither of those two measures are as important as they used to be. So, why haven’t we switched to decimal time?  Well, once again, I blame the French!

Starting in the 1750s a handful of philosophers and mathematicians began to write about their struggles with the base 12 system.  After all, we have ten fingers and, in a time when people counted rather than computed, it seemed counterintuitive to use a non-base system of weights and measures. What is the logic of having 12 inches in a foot or 14 pounds to a stone?

When the French revolted against the monarchy (and practically everything else), the political upheaval spread well beyond politics.  After the storming of the Bastille, the French nobility made many concessions to the revolutionary forces, among which was relinquishing control over what were official weights and measures. (If you control how things are measured, you can control the economy.) This became the first major foray into the metric system, but it didn’t stick.  (France dropped this precursor to the modern metric system in 1812 and re-adopted a new one in 1837.) 

These early metric system revolutionaries weren’t only concerned with pounds and inches; they also tried to reform the minutes and hours, using something now called “French Revolutionary Time” or “French Republican Time.” The idea was simple — ten-hour days, with each hour consisting of 100 minutes, and each new minute made up of 100 seconds. They also renumbered the years beginning with the year “1” in 1789, and reset the months in the calendar.  It was all a nice neat little package.

On November 24, 1793, this base 10 system became the law of the land, and clockmakers began to produce special clocks.  Gone were seven-day weeks — they were replaced by a ten-day week. Each month was now 30 days, no more, no less, each made up three weeks. There were still 12 months, in order to make the math work out correctly (roughly), but each month was renamed to reflect the seasons as experienced by someone in Paris. Five or six (on leap years) celebratory days came at the end of the year, bringing us to the same 365 days in the current calendar.

Or, at least, that was what the law said. In practice, people didn’t really care to change how they kept time.  Like the US’ steadfast persistence with the Imperial System (pounds and ounces, feet and inches, degrees Fahrenheit, etc.)  trade continued to be conducted in the old weights and measures.  There were few practical reasons for non-mathematicians to change how they told time. The base 12 system was good enough — plus, their clocks didn’t need to be replaced, which sounds like a silly reason, but the cost of changing over every single clock was significant.

Failing to get the people on board, the new government ultimately gave up the effort. The decimal time experiment lasted less than 18 (regular) months; by spring of 1795, the French leadership dropped the edict.  Vive la Revolution – sort of (mehe).