Though a noble and nominally a clergyman, Bishop Charles Maurice de Talleyrand sided with the revolutionaries at the start of his long political career. Better known for his diplomatic success at the Congress of Vienna in 1815, it was he who proposed the metric system to France's National Assembly.

Courtesy Chateau de Rochecotte __1790: __The French National Assembly decides to create a decimal system of measurement. The metric system is born.

This came after the storming of the Bastille but still before the declaration of a republic and the execution of King Louis XVI. But revolution was in the air: "National Assembly" was simply the new name the upstart Third Estate had given itself.

The assembly was acting on a motion by Bishop Charles Maurice de Talleyrand. Under the ancien régime, France measured with an inch, foot and fathom (pouce, pied and toise) about 6.6 percent larger than their English counterparts.

The first meter was based on clockmaking: the length of a pendulum with a half-period (a one-way swing) of one second. Responding to a proposal by the French Academy of Sciences, the assembly redefined the meter in 1793 as 1/10,000,00011 of the distance from the Equator to the North Pole.

The system was elegant. All conversions were based on 10, with Greek prefixes (deka-, hecto-, kilo-) for multiples and Latin (deci-, centi-, milli-) for fractions. The gram unit of weight was defined by the weight of one cubic centimeter (aka milliliter) of water.

The new "Republican Measures" became legal throughout France in 1795 and were made compulsory in 1799 when definitive platinum meter bars and kilogram weights were constructed. But resistance to the new measures lasted for decades.

France also used a quasi-metric Revolutionary Calendar with each month consisting of three décades of 10 days each. (Revolutionaries even attempted a metric day of 10 hours of 100 minutes each of 100 seconds each.) But Napoleon returned France to the Gregorian calendar in 1806.

The current International System of Units – or SI, for Système International – is based on the Treaty of the Meter signed in Paris on May 20, 1875. The United States was a signatory, and the metric system is the legal system in this country, although the legal alternate English system remains more widely used. (An online conversion engine can make translation easy.)

The meter was formally redefined in 1960 as 1,650,763.73 wavelengths in a vacuum of the orange-red light radiation of the krypton 86 atom (transition between levels 2p10 and 5d5). The new standard was 100 times more precise than the old. The current definition, adopted in 1983, makes the meter the distance traveled by light in a vacuum during 1/299,792,458 of a second.

That's 39.37 inches to counter-revolutionaries.

Source: Various

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