July 15, 2024

The First Metre

It is hard to imagine, but at some point in history, someone sat down and invented the metre. And its origin story, is surprisingly lively.

King Louis XVI

On July 14, 1789, an angry mob assembled in Paris, and marched on the Bastille, a military fortress and prison in the heart of the city.

Their enmity had been provoked by events in Versailles; a small town about 25 miles from Paris, and location of the royal court of King Louis XVI. Over the preceding few weeks, The King had been meeting with the ‘Estates-General’, a kind of pseudo-parliament consisting of appointed nobles, clergy, and a few commoners.

The subject of these meetings was to provide the King with finance.

France was in the grip of a debt crisis, and the crown had effectively run out of money.

The Estates-General were willing to provide credit to the King, but not without certain conditions; chief among them, greater political freedom, the establishment of a full, elected parliament, and a reduction in taxation.

King Louis initially reacted with hostility to these proposals, rejecting a reduction of his powers.

The storming of the Bastille; July 14, 1789

As rumours swirled that the King was about to disband the Estates-General, the mob in Paris rose up in opposition. They broke into the lightly guarded Bastille, a prominent symbol of royal authority, seized the large cache of weapons kept there, and freed a handful of prisoners from the cells.

Later, they rampaged through the streets of the city, killing several soldiers, and decapitating Paris’ mayor, who they cornered at the luxurious Hotel de Ville.

It was the beginning of The French Revolution.

The revolutionary National Assembly

Revolutionary activity would continue for a decade.

The most obvious outcome was the transformation of the French political hierarchy. King Louis, and his wife, Marie Antoinette, were executed in 1795, and the monarchy was replaced by a National Assembly of elected representatives.

But the instigators of the French Revolution didn’t just want political change; the Revolution was also required to deliver a re-imagining of French society. The National Assembly aspired to a new world order; designed fairly and logically, with laws based on sound scientific principles and detailed analysis.

And one small part of this transformation, was the metric system.

Fully extended, this instrument measured one 'Pier du Roi'

The existing system of weights and measures used in France seemed almost designed to give affront to the coolly rational minds of the Revolution.

There was no standardised set of measurements in use at all, in fact. Instead, there were some 800 different units of measurement, that varied from region to region across the country.

These ranged from familiar terms like feet and yards, to more exotic items like leagues, and the posh sounding ‘Pied du Roi’, AKA ‘The King’s Foot’. The conversion rate between one unit and another was complicated; one league equalled 13 200 feet, and even then, this rate could vary from one location to the next.

Most of these units were leftovers from the Roman occupation of the country centuries beforehand.

And so, in 1790, as the National Assembly grappled with re-writing the French constitution and the future of the monarchy, they also undertook to design a new system of measurements.

The grande Academie Francaise, home to the Academie des Sciences

The Académie des Sciences, France’s leading scientific institution, was charged with the task.

They deliberated for a year, and finally recommended that France design an entirely new system from scratch, creating new, decimal units of measurement.

Under this proposal, all units would be designed on a base 10 system, meaning that increases from one unit to the next would occur at multipliers of 10, 100, or 1000. These new units of measure, once defined, would be mandatory and standardised across the country.

The starting point would be to define one unit of measure, and then base all of the others off this. This first unit of measurement was to be one of length, and it was to be called the 'metre'.

The Metric System; full version

The word ‘metre’ comes from Ancient Greek; ‘metreo’, meaning, ‘to measure.’ Now it would lend it's name to an entire system of measurement; 'metric', meaning, 'derived from the metre'.

But rather than simply select a value for the metre, in keeping with the spirit of the times the Academie also determined that it should be derived scientifically. After much debate, it was decided that a metre should be equivalent to one ten millionth the distance from the equator to the North Pole.

While calculating this distance would be formidably difficult, the designers of the metre believed that a value based on nature would be more robust, and more easily comprehensible to lay people. But how to go about calculating the distance from the equator to the North Pole?

Enter Pierre Mechain and Jean-Baptiste Delambre.

Mechain (left) and Delambre; dogged scientists

Mechain and Delambre were distinguished astronomers, and well-known to the scientific community in France.

Their plan was to accurately measure part of the overall distance from the equator to the North Pole; a 1000 mile stretch of territory from northern France, to central Spain. Once this distance had been measured, they could extrapolate the remaining distance from the result.

Using the southern French town of Rodez as their fulcrum, Delambre would lead a surveying team north to Dunkirk, while Mechain headed south to Barcelona.

Rodez, southern France

The first stage of the project was almost absurdly laborious.

Mechain and Delambre set out on foot, with precisely measured metal bars, and manually placed these in sequence along the road. They used a historical unit of measure, the ‘ligne’, with the intention of converting this to metres, once the work was complete.

Very slowly, this approach began to produce an accurate measure of distance, between one town and the next.

After this initial phase had produced enough data, the two dogged scientists could then use this information to calculate longer distances using a theodolite and standard surveying mathematics.

But progress was slow.

The Pyrenees Mountains

Mechain, in particular, faced great difficulties.

His route south passed through the Pyrenees, and the rugged terrain proved difficult to navigate, while changes in height above sea level complicated his calculations.

Crossing the border into Spain, Mechain was then arrested. The French revolutionary government was viewed with suspicion by other European countries, and the local authorities initially thought he was a spy.

His mission – to accurately measure a small part of the Earth’s surface – sounded entirely implausible. Mechain was eventually released  when no evidence could be found against him.

In the end, it would take Mechain and Delambre six years to complete their surveying mission.

One of 16 'metre bars' that were installed in Paris, in 1798.

In November 1798, the two scientists returned to Paris to combine their data.

Their measurements were very nearly identical, and they were quickly able to settle on a value for the metre of 443.296 lignes. Several platinum bars of this length were struck, which were put on public display to familiarise people with the new unit.

Other units of length, the kilometre and the centimetre, could then be defined. The metre was also used to calculate the initial value for the gram, which lead to other new units of weight.

In December 1799, the National Assembly passed the new system into law, and outlawed use of any other units of measure. The metric system had arrived.

But the story, was not quite over.

Napoleon Bonaparte

As the French Revolution descended into chaos at the end of the 18th century, Napoleon Bonaparte assumed control of the French government.

Napoleon was a career soldier, who had found fame as a successful general in the Revolutionary wars, defending France from invasion by their European neighbours. Backed by the army, who viewed him as a strategic genius, Napoleon staged a military coup, and assumed control of France in November 1799.

Napoleon himself was not a fan of the new metric system, viewing the matter as ‘trivial’. Among many changes wrought during his rule, in 1812 he reversed the abolition of the old units of measure, and allowed the metric and historical systems to exists, side-by-side.

Louis-Philippe I; the last king of France

After Napoleon was deposed, in 1815, France reverted to a Constitutional Monarchy, with an elected Parliament capped by a royal head of state.

In 1837, under King Louis-Philippe I, the Parliament restored the metric system to pre-eminence, and began a lengthy, 20 year program of phasing out the old measurements; this time, for good. While Louis-Philippe was deposed in another revolution in 1848, and so was the last king of France, this time the metric system would remain.

Other countries soon recognised the value in such a simple, logical system, and use of metric units began to spread.

Countries that have resisted the metric system

As of the present day, only three countries have not adopted the metric system as their formal system of measurement; Burma, Liberia, and the United States.

The metre, the foundation stone of the system, is now defined as, ‘the distance that light travels in 1/299792458 second’.

This more accurate definition, adopted in 1983, differs from Mechain and Delambre's original calculation by a fraction of a millimetre.


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