Before the SI units
Before the SI units we have today, we had the imperial system, but not the same one as the one used in the USA today. The earliest known measurement was the cubit, which was the average length of a forearm. The ancient egyptians defined the royal cubit as the length of the pharoah’s forearm. Measuring sticks were made for the royal cubit and distributed among builders. An inch was 3 kernels of barley stacked end to end. An acre was about the amount of land a yoke oxen could plow in one day. The yard was the length around a certain king’s chest. The mile was 1000 paces of a roman soldier.
Most measurements back then were defined by arbitrary quantities relating to agriculture or anatomy. For old applications, such as building huts and fences, those measurements were actually more useful than strictly defined measurements, as having a forearm was and still is far more common than always having a ruler on hand. However, in France alone, there were 800 measurements, and 250000 unique definitions for them. Measurement in Europe was a mess.
The foundation for the metric system
During the French revolution, which spanned from 1789-1799, the French were overhauling many things in France, and they decided it was time to standardize measurement. The great variation in measurement definitions caused unnecessary confusion and was impractical for trade.
A French clergyman called Charles Maurice de Talleyrand heavily pushed for a new system with constant values based on natural units, proposing the idea of developing such a system to the French National Assembly in 1790. Talleyrand was positive that such a system would be welcomed with open arms, and wanted to involve other countries in its creation.
Great Britain ignored the invitation to cooperate, so the French Academy of Sciences decided to do it on their own and set up a commission, which decided that the length unit should be based off of the size of the Earth. They eventually decided to make the meter a 10 millionth of the length of a median arc through Dunkirk. The system was to be a base 10 system, so many calculations would simply require moving a decimal point.
However, measuring a quarter of the Earth’s circumference in 1790 was no easy feat. Rather than that tedious task, they decided to measure the length of a meridian arc stretching from the norht of Dunkerque to the south of Barcelona. While it was easier, measuring that distance was still very tough. In 1792, two geodesists, Delambre and Méchain set out to measure this distance.
The astronomers ventured into the countryside, looking for vantage points, such as tall hills or castle towers, and waited until the skies were clear. Using triangulation, with an instrument called the repeating circle (Cercle répétiteur) they made triangles along the line, then calculated the distance through trigonometry.
In 1799, after 7 whole years, they completed the task and defined the meter as one 40 millionth of the Earth’s circumference. The word ‘meter’ was derived from the Greek word ‘metron’, which meant ‘to measure’. These measurements were quite precise, but due to a small calculation error along the way, the meter is about 0.2 mm shorter than it was supposed to be.
Having the standard unit of length and a base 10 system was great, but they needed a way of differentiating the different units of length. This was done using prefixes. Bigger prefixes, such as deca- (101), hepto- (102), kilo- (103), mega- (106) were based on greek words, while smaller prefixes such as deci- (10-1), centi- (10-2), milli- (10-3), micro- (10-6) were based on latin words.
From here, other base units were defined. The base unit for volume, the liter, is equal to the volume of a cube with 10 centimeter sides. The base unit for mass, the kilogram is equal to the weight of a liter of water.
Officialization of the system
Two patented prototypes were made; a weight with a mass of one kilogram and a bar with the length of a meter, both of which were put in the French National Archives. This system was named the metric system, and deemed the legal standard on the 10th of December, 1799. While this change was not initially well received, people began to warm up to the metric system over time.
Over time, the rest of Europe started to adopt the metric system, and spread it to the rest of the world. As more and more of the world adopted the system, a big issue arose. Bars the length of a meter were distributed among the countries, and through regular use, the ends would slowly chip away until the bar began getting inaccurate.
In 1875, an international conference met in Paris and established the International Bureau of Weights and Measures. There, they decided to have a permanent laboratory in Sèvres, near Paris, where international standards are preserved and metrological research is conducted. For convenience sake, the meter and kilogram were still based on the archive standards rather than actual measurements for quite a while.
Three more units were made in 1948: The newton, a unit of force defined as the force which gives a mass of one kilogram an acceleration of one m/s2; The joule, a unit of energy defined as the work done when a force of one newton displaces an object one meter in the direction of the force, and the watt, a unit of power which is the power that in one second uses an energy of one joule. All three units are named after scientists.
That was until 1960, when measurements were once again defined by natural constants. The meter was redefined as 1,650,763.73 wavelengths of the orange-red line in the krypton-86 spectrum, and redefined once again in 1983 as the distance traveled by light in a vacuum in 1/299,792,458 of a
second. The kilogram and second had similarly complex and convoluted definitions, but the new definitions were precise and completely unchanging.
Up to this point, the centimeter-gram-second and meter-kilogram-second systems were the primary systems. However, along with the redefinition in 1960, the International System of Units was established. The SI units are comprised of 22 units, which are derived from 7 base units: The meter for length, the kilogram for mass, the second for time, the ampere for electric current, Kelvin for temperature, the mole for amount of substance, and the candela for luminous intensity.
The metric system in the current day
In the current day, almost every country in the world has adopted the metric system, with the exception of the United States, Liberia, and Myanmar. In the case of Liberia, it’s quite simple, as they used to be a colony of the U.S. and inherited the imperial system from them. Myanmar never officially adopted the metric system. The fact is, Liberia and Myanmar are in the process of metrication, having started in 2018 and 2013 respectively.
The case of the U.S. is a little more complicated. They didn’t switch initially because when the U.S. first became independent, Great Britain was still the U.S.’s primary trading partner, and it made sense to keep the system in place. While the U.K. eventually started using a mixture of both, the U.S. continued to make their infrastructure with the imperial system in mind.
Whenever the imperial system started to become inconvenient as trade in the U.S. expanded, businesses simply used conversion rates. While there were several attempts to standardize the metric system throughout history, these all failed as Americans viewed the idea of switching as unpatriotic and anti-American. They believed that the U.S. was the best nation, and the metric switch would ruin the country.
Currently, the switch is not being fully made because transferring all the measurements (street signs, products, prices, e.t.c.) would cost a lot and be a hassle. Moreover, many industries rely on the imperial system, making the switch even more tedious. However, contrary to popular belief, the metric system is very commonplace in the U.S. The Metric system is used for trade and science in America, as it is far more comprehensive for its purposes and clears up confusion between scientists worldwide.
The imperial system in the current day
Currently, the Imperial system is still used in many ways. The first and most obvious way is that Americans still use it in their day-to-day life. A more general use is that most bakers and ovens use Fahrenheit, as while there isn’t really much logic to it, it allows for much better temperature control, due to each degree Celsius being 1.8 degrees Fahrenheit. Strangely enough, the imperial system technically has no meaning. The only definition of an inch is 2.54 cm, meaning that imperial measurements rely on the metric system.
Sources
Usma – Origin of the metric system
Youtube – [1], [2], [3]
Britannica – [1], [2], [3]
Bookofthrees – The repeating circle
Research gate – The Triangulation of France
NIST – SI Units
Ubique – Countries that don’t use the Metric System
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