On the facade of the Ministry of Justice in Paris, just below a ground-floor window, is a marble slab inscribed with a horizontal line and the word “MÈTRE”.
It is hardly noticeable on the stately Place Vendôme – in fact, of all the tourists on the square, I was the only one to stop and meditate on it.
But this painting is one of the last “Scale” (Standard Metric Rods) were placed around town over 200 years ago in an effort to introduce a new global system of measurement.
It is just one of the many sites in Paris that refer to the long and fascinating history of the metric system.
Ken Alder, professor of history at Northwestern University in the United States and author of measure everything, A book on the construction of the metro.
It is now a matter of course in most places: the metric system, which was created in France, is the official system of measurement in almost every country in the world, with the exception of the United States, Liberia, and Myanmar. And even there, the metric system is still used for purposes such as global trade.
But imagine a world where every time you travel you need to use different conversions for measurements, as we do with currencies.
This was the case before the French Revolution in the late eighteenth century, when weights and measures differed not only from state to state, but also within states.
In France alone, it is estimated that at that time there were thousands of different units of weights and measures in use.
The French Revolution changed that.
During the turbulent years from 1789 to 1799, revolutionaries sought not only to overthrow politics, seize power from the monarchy and the Church, but also to fundamentally change society by overturning old traditions and customs.
To this end, they introduced, among other things, the Republican calendar in 1793, which consisted of 10 hours per day, with an average of 100 minutes per hour and 100 seconds per minute.
In addition to eliminating the religious influence of the calendar, which made it difficult for Catholics to keep track of Sundays and Holy Days, this helped introduce the decimal system in France.
But while the decimal clock has not moved forward, the new decimal measurement system, which is the basis of the meter and the kilogram, is still with us today.
The task of creating a new measurement system was entrusted to the most prominent scientific thinkers of the Enlightenment.
These scholars were eager to create a new unified system based on reason rather than tradition or the will of local authorities.
Therefore, it was decided that the counter should be based on pure nature. It was supposed to be a ten-millionth part of the distance from the North Pole to the equator.
The longitude from pole to equator, which would be used to determine the length of the new standard, was the Paris longitude.
This line was drawn by two astronomers who left Paris in 1792: Jean-Baptiste Joseph Delambre, who traveled north to Dunkirk, and Pierre Michen, who traveled south to Barcelona.
They used the latest technology of the time and the mathematical process of triangulation to measure the meridian arc between these two locations at sea level.
Then, after extrapolating the distance between the North Pole and the Equator, by extending the arc to the ellipse, the astronomers agreed to meet within a year in Paris to propose a new global standard of measurement.
The process ended up being seven years old. Finally, in 1799, Delambre and Méchain presented their results, and based on them, a one-meter platinum strip was created as the basis of the metric system.
As Alder details in his book, measuring this meridian during a period of great political and social turmoil has proven to be an epic task.
The two astronomers were often met with suspicion and hostility. They fell into the blessings and shame of the state. They even got injured in action, which included climbing high points such as church domes.
The Pantheon, commissioned by Louis XIV to be a church, became the central geodesic station in Paris – from its dome, Delambre triangulated all points around the city.
Today, it serves as a mausoleum for the heroes of the Republic, such as Voltaire, René Descartes and Victor Hugo. But in the days of Delambre it served as another type of shrine – a storehouse of all the old weights and measures that were sent from cities through France in anticipation of the new order.
But despite all the efforts and technology invested in defining the new procedure, no one wanted to use it.
People were reluctant to abandon the old methods of measurement, as they were closely related to rituals, customs, and the local economy.
For example, a measure of ell, of cloth, was usually equal to the width of a domestic loom, while arable land was often measured in days, referring to the amount of land that a peasant could prepare during that time.
The Paris authorities were so upset by the public’s refusal to leave the old procedure behind that they sent police inspectors to the markets to ensure the new system was in place.
Finally, in 1812, Napoleon abandoned the metric system; Although it was still taught at the school, people were allowed to use whatever measurements they wanted until the metric system was reinstated in 1840.
According to Ken Alder, “It took about 100 years for all the French to start using it.”
But this is not only due to the perseverance of the state.
France was advancing rapidly towards the Industrial Revolution. Cartography requires more precision for military purposes; And in 1851, the first major world fairs were held, at which countries had to present and compare industrial and scientific knowledge.
Of course, this was difficult unless you had clear standard measurements such as meters and kilograms.
For example, the Eiffel Tower was built for the Universal Exposition of 1889 in Paris, and at a height of 324 meters it was at that time the tallest man-made building in the world.
All this led to the creation of one of the oldest international institutions in the world: the International Bureau of Weights and Measures (BIPM, acronym in French).
BIPM is located in the quiet suburb of Sèvres in Paris, surrounded by parks and gardens. Remind me of your lack of bragging again Scale in Place Vendôme; It may be hidden, but it is fundamental to the world we live in today.
BIPM was originally created to maintain international standards, and promotes the standardization of seven international units of measurement: metre, kilogram, second, ampere (which measures the intensity of electric current), kelvin (the unit of temperature), mole (amount of substance) and candela (intensity of illumination).
This is where the platinum standard meter tape is used, to carefully calibrate the copies, which are then sent to various other national capitals.
In the 1980s, the BIPM redefined the scale as the distance light travels in a vacuum in a specified amount of time, making it more accurate than ever.
Since then, it has been determined by the universal laws of physics, and has finally become a nature-based analogy.
The building at Sèvres also houses the original kilometer, which is located under three vaults in an underground vault, and which can only be accessed by three different switches, held by three different people.
Now, the kilogram is calculated by a so-called Kibble (or Watt) scale, an instrument that allows the comparison of mechanical and electromagnetic energy using two separate experiments.
This method of measuring the kilogram does not change, it cannot be damaged or lost, as can happen in the case of a physical body.
Moreover, a definition based on a constant – not an object – makes the exact measurement of the kilogram, at least in theory, available to anyone anywhere on the planet, not just those who have access to the original kilogram stored in France.
As with the 18th century longitude project, determining measurements remains one of our most important challenges.
What started with the metro formed the basis of our modern economy and led to globalization. It paved the way for high-resolution engineering and remains essential to science and research, as well as our understanding of the universe.
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