Taking Measure

Several historians have described the American Revolution as the “American Secession”. This is because the American Revolution was pretty tame compared to later revolutions in France and Russia. Most Americans weren’t even in favor of the Revolution, and the majority of those that were didn’t want to change their entire world… they just wanted the British to leave them alone. So after the British left, life continued for most Americans more or less as it had for decades.

Contrast this with the French Revolution, where revolutionaries railed against a millennia of rule by a theocratic monarchy. Most of France belonged to the monarchy or aristocracy, and much of the rest belonged to the church. From a revolutionary point of view, it wasn’t enough to just change their form of government. Society had to be recreated from the ground up, and certain people needed to be gotten rid of or “re-educated”. So aristocrats, bishops and priests were executed by the thousands, and their wealth and property redistributed to the working class.

But even that wasn’t enough. French revolutionaries created a new calendar to eliminate religious and monarchical days. The calendar would start not from the birth of Jesus, but from the founding of the Republic. Revolutionaries even invented a new decimal clock, partly because of its perceived ease of use, but also as another way to eliminate all traces of the Ancien Régime.

Many reforms weren’t very popular. Decimal time became the “official time” of a handful of towns, and was readily embraced by a few scientists and revolutionaries… but almost no one else. The Republican calendar was more successful, being used by the French government for 12 years. There was, however, a significant error in the calendar related to the calculation of leap years which made it mathematically inaccurate. And while many Frenchmen were at least initially more enthusiastic about the calendar than the clock, so many people had to use the Gregorian calendar so often – in business dealings with other countries, or working with dates from before the Revolution – that most just gave up and went back to the old calendar. For some reason, I’m picturing an 18th century French version of Lewis Black, complete with liberty cap: “we already had one perfectly good calendar, but invented a new one… SO WHY THE HELL DO WE KEEP GOING BACK TO THE OLD ONE? IF EVERYONE’S GONNA KEEP USING THE OLD ONE, WHY DON’T WE JUST DITCH THE NEW ONE? AM I THE ONLY SANE PERSON IN THIS REPUBLIC??”  In any case, the French government agreed and went back to the Gregorian calendar in 1805.

But there was one reform that was insanely popular. It was so popular, in fact, that almost the entire world now uses it. And people in France at the time were happy to see it.

It’s the metric system.


The first unified system of measurement used in France was established by Charlemagne in AD 790. His system was remarkably similar to Britain’s “Imperial System”. For instance, the pouce was the French equivalent of the inch, and was exactly 1.066 inches. And the pied du roi (“the king’s foot”, usually just shortened to pied) was equal to 12 pounce (12.86 inches, or 1.066 feet). Thus, the pied carré (square foot) was equal to 1.136 sq ft. The toise, the French equivalent of the fathom, was 6.394 feet, compared to 6 feet in England (the English only used fathoms at sea; the French used it on both land and sea). Liquid measurements varied a bit: the chopine was equal to .84 Imperial pints (but almost exactly 1 US pint, which was the system in use in England until 1824), the pinte was 1.86 Imperial pints (or 2.01 US pints). The quade was equal to a US half-gallon (or .42 Imperial gallons) and the velte was equal to 2.01 US gallons (or 1.68 Imperial gallons).

But then Charlemagne had to go and die, and the whole system fragmented into a million pieces. Units of length and area measurement were especially affected by fragmentation: there was one system used in Paris, another in Quebec, and another used in the rest of France generally. But it’s a stretch to say “France generally”, as measurements could vary widely. For instance, the lieue (league) was 3.63 miles in Provence but 2.03 miles in Beauce. What’s worse is that names could vary, too. In Pernes-les-Fontaines the unit of measure called the livre was what the rest of France called the livre du roi. In fact, many historians estimate that there were as many as 800 different names for the different types of measurement.

It gets worse. It wasn’t unheard of for kings or local aristocrats to tinker with the existing system to their advantage. A large landowner, for example, might have redefined the livre (pound) as being 20 once (ounces) instead of the traditional 16. When it came time for peasants to harvest the landowner’s crops, he would measure their labor in the “new” livres, then sell the crops on the open market using the old livres, thus cutting his labor costs by 25%. Other landowners would hear about such a thing and tweak the livre to their own needs as well.

But it wasn’t always greed that caused measurements to change. Many technologies and industries sprang up after Charlemagne’s time, requiring new types of measurement. Sometimes folks would invent new units, while other times they would co-opt existing measurements. The manufacture of cloth, for instance, was largely a cottage industry during Charlemagne’s reign, but became industrialized in the centuries following his death, So the industry invented the aune as a unit of measure for the cloth trade. And sometimes the simple passage of time required new units of measure. In 1688 it was discovered that the “reference standard” of the toise – the actual, physical piece of metal by which the toise was officially defined – had shrunk. So a new unit, 11 mm shorter that the previous toise – was created to accommodate this. It was called the toise du Châteletm and it was used until the almost identical toise du Pérou was introduced in 1747.

Needless to say, by the late 1700s, the whole system was a gigantic mess. It’s estimated that there were over 250,000 different units of measure being used in France at the time of the Revolution. Citizens had a difficult time knowing how much bread or meat they were buying, and if they were getting ripped off. Even aristocrats, with all their education and lawyers, had a tough time of it. It’s no wonder that “reforming the measurement system” was at or near the top of every cahiers de doléances, a list of grievances each town and village in France submitted to the king in 1789, in the early days of the Revolution.

In the early 1790s, Charles Maurice de Talleyrand-Périgord (known to history as just “Talleyrand”) approached the British and Americans for help in developing this new system of measurement. The savants of France had come up with a great idea: a system of measurement using decimal, base 10 numbers, with divisions and multiples using easy to remember Greek prefixes. Even though France and Britain had been enemies for centuries, the French savants wanted one unified system of measurement for the entire world. Wouldn’t it be great, they thought, if Britain joined them?

The only problem was… Britain didn’t have a problem. One of the many demands of Magna Carta was for a single unified system of measurement. When King John signed the document in 1215, the “Imperial System” became the law of the land. And as clunky as the Imperial System was, by the 1790s the English had been using it for over 575 years, and it had worked very well for them, thank you very much. So they opted out of the new system.

America was slightly more receptive to the idea. At least, some Americans were. Republicans were big supporters of the idea (and by “Republicans”, I’m talking about fans of Revolutionary France who would become known as “Jeffersonian Democrats”, not the current Republican party… which wasn’t founded until 1854). But America was dominated at the time by Federalists, a party immensely loyal to Britain. They recognized Britain, not France, as America’s biggest trading partner, so why switch to a French system when America’s financial future was with Britain? And most Federalists looked at the French Revolution with fear and trepidation. They were the ones who didn’t want to change American society, they just wanted independence from Britain. Changing the calendar? Executing priests? All horrific French ideas that caused deep suspicion of anything French in Federalist minds.

So the French decided to go it alone. Article 5 of the law of 18 Germinal, Year III (that’s April 7, 1795 to you) defined the new measurements as the metre (length), the are (100 m2, for land), the stère (1 m3, for firewood), the litre (for liquids), and the gram (for mass).

But, like most things in the History Blog, there was a problem. The metre was defined as “one ten-millionth of the distance between the North Pole and the Equator through Paris”, and such a thing hadn’t actually been measured yet. And since all other units of length were based on the meter, the government needed to come up with actual numbers ASAP. So the revolutionary government temporarily defined the metre as 443.44 lignes using figures from a survey conducted in 1744 by César-François Cassini de Thury (known as just “Cassini”), But what was really needed was for someone to actually go and measure the distance.

The task of measuring the Paris meridian fell to Jean Baptiste Joseph Delambre and Pierre Méchain (actually, Cassini had been chosen over Delambre, but Cassini, a royalist to the core, refused to work for the revolutionary government after it arrested Louis XVI in 1792).

The job was split in two, with Delambre surveying the northern half from Dunkirk to Rodez, and Méchain surveying the southern half from Barcelona to Rodez. Delambre arguably got the better end of the deal: whilst his portion was twice as long as Méchain’s, it was largely on flat ground that had been surveyed several times in the past. Méchain, meanwhile, had to contend with the Pyrenees mountains and several parts of Spain that had never been surveyed before.

The two ran in to trouble several times. There were plenty of technical problems, like broken equipment or bad sightlines that prevented triangulation. But there was more, like superstitious peasants starting riots because they couldn’t tell if the two were up to witchcraft instead of science. The two were also jailed multiple times by local royalist\revolutionary governments who accused them of being revolutionary\royalist spies. It took six long years, but the work was eventually done.

And here’s the big kick in the pants: Méchain’s numbers didn’t add up. He became trapped in Spain when that country declared war on France on March 7th, 1793. With nothing else to do, Méchain surveyed the land near Barcelona again to verify his findings… but those results differed from his first measurement. Again and again and again he went over the numbers, but he could never replicate his first result. He submitted his first measurements to the French government, but kept the second measurements a deep secret.

It was a secret that would torture him. He went over the numbers again and again and again, trying to figure out what he’d done wrong. While his government hailed him as a hero who’d conquered nature with human reason, creating a unit of measure “for all people, for all time”, Méchain knew he’d messed up somewhere. It positively haunted him, and drove him to the brink of madness. He returned to Spain in 1804 to try and figure out what he’d done wrong. Sadly, he contracted yellow fever and died before he could figure out what had happened.

Delambre was given Méchain’s notebook’s after his death. Méchain’s error might have gone undetected forever, had Delambre not noted in the margin of one of the pages that the numbers didn’t add up. Delambre chose to keep Méchain’s secret because “after all, does it matter if it is wrong? And can the meter be wrong?”.

In the end, Méchain’s error didn’t amount to much anyway. In 1806, a pair of astronomers surveyed the Mediterranean island of Formentera and found that Delambre and Méchain’s measurements were just a hair too short. The scientific community simply accepted the error, and continued to use Delambre and Méchain’s measurement until 1867, when the International Conference on Geodesy (imagine what their parties were like!) called on scientists to create a new standard.

On May 20, 1875, the Metre Convention was signed in Paris. This created the Bureau international des poids et mesures (BIPM), which would be responsible for creating the “new” meter. And the technology behind this “new meter” was surprisingly complex, especially when you consider that they were just making a metal rod. It was decided, for instance, that the rods should be made of an alloy of 90% platinum and 10% iridium; this was an extremely strong alloy not subject to warping. And the rods would be longer than a meter, with the length of the meter marked off in lines on the bar (instead of just having the bar itself be exactly 1m long); this would minimize inaccuracy from wear on the ends. And the rods would be in a special X shape (called a Tresca section) to eliminate torsional strain.

As cool and high-tech as this was, in a few decades it was dropped for the “krypton standard”, which defined the meter as

“the length equal to 1,650,763.73 wavelengths in vacuum of the radiation corresponding to the transition between the levels 2p10 and 5d5 of the krypton 86 atom.”

By the 1960s, this too was dropped in favor of the “speed of light” standard, which is still the standard today:

The metre is the length of the path travelled by light in vacuum during a time interval of 1/299,792,458 of a second.

Amazingly precise. And all the more interesting coming from a country that once had 250,000 different units of measurement, and who hired a man to fix it… but who was was haunted by an error.

Liberté, égalité, fraternité        un seul système de mesure unifié?


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