France Adopts the Metric System
The adoption of the metric system in France on April 7, 1795, marked a significant achievement of the French Revolution and the Enlightenment's emphasis on rationality and uniformity in measurement. Historically, France, like much of Europe, relied on a patchwork of local measurement systems, which complicated trade and governance. The new metric system introduced a standardized, decimal-based approach that simplified calculations and fostered scientific inquiry. The meter, defined as one ten-millionth of the distance from the North Pole to the equator, became the foundational unit, along with the gram for mass and the liter for volume.
Despite its advantages, such as ease of use and logical structure, the metric system faced resistance, particularly in Great Britain, which retained its traditional units until the late 20th century. Over time, the metric system evolved into the Système Internationale d'Unités (SI), further refined to enhance precision, such as defining the meter based on the speed of light. While the metric system is globally dominant in science, engineering, and international trade, cultural attachments to traditional measurements persist in certain regions. Today, only a few countries, including the United States, continue to use non-metric systems, highlighting the ongoing tension between tradition and standardization in measurements.
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France Adopts the Metric System
France Adopts the Metric System
The metric system, formally adopted by France on April 7, 1795, would prove to be a permanent achievement of the French Revolution and Enlightenment science and philosophy. Over the centuries it would spread around the world, so that it is now the dominant system of weights and measures in use.
Like the rest of Europe, France had historically relied on ancient systems of weights and measures which had been inherited from dimly remembered antiquity. These customary measurements varied not only from region to region but even from town to town, hindering trade and science and presenting an obstacle to centralized government. Further, since each unit of measurement was unique, its relation to other units of the same type, but of greater or lesser magnitude, was fairly arbitrary. Formulas of relationship could not be logically deduced but had to be memorized (12 inches to a foot, 3 feet to a yard, 5-1/2 yards to a rod, etc.).
On May 8, 1790, the French National Assembly approved a proposal for the creation of a uniform, decimal system of weights and measures. The base for this system of measurement became the meter, one 10-millionth of the distance between the North Pole and the equator, as carefully calculated by scientists in Paris. On April 7, 1795, the new system based on this meter was formally approved. Other uniform measurements followed, such as the gram for mass and the cubic centimeter for volume. Because the metric system is arranged in decimal increments and has other logical features, it became the favored system for scientific use and for use in such other matters as international trade, with the result that it spread rapidly in Europe. However, Great Britain, France's enemy during the Napoleonic wars, retained a system of customary weights and measures both at home and in its colonies. Britain did not convert to metric till 1995, and until then the English, or Imperial, system was a formidable international alternative to metric.
Meanwhile, the meter itself was undergoing refinement. The French scientists who had constructed the metric system in the first place had sought to base it on some constant in the natural world. However, nature proved to be more changeable and irregular than anyone had expected. Upon discovering that the Earth was not a perfect sphere after all, the scientists abandoned the attempt to define the meter mathematically and simply defined it as the distance between two marks incised on a particular bar of platinum-iridium alloy, which was kept in a vault near Paris. This sufficed as the world standard for nearly a century, but eventually something more precise was needed and the search resumed for a natural constant. In 1960 the meter was redefined in terms of the wavelengths of orange-red light given off by krypton-86, a rare substance, but since 1983 it has been defined as the distance traversed by light passing through a vacuum in a tiny fraction of a second (approximately one 300-thousandth). The revised metric system is called the Système Internationale d'Unités, or SI. Its precision and its ease of use have made it invaluable to scientists.
The metric system nevertheless has certain drawbacks. It echoes the 10-based system used in counting, and it shares the defects of that system. Ten cannot be perfectly divided into thirds, and even fourths necessitate fractions or decimal points. Systems based on 12 are more flexible—12 can be divided into halves, thirds, fourths, and sixths all in whole numbers, and some of its multiples offer an even wider range of possibilities. Many of the traditional units of measurement—the foot, the yard, the gallon, and of course many measures of time—are based on four, twelve, or sixty, and reflect the need for simple ways to divide. More significantly, however, the old measurements have deep roots in traditional culture, and people have an affection for them.
Advocates of the metric system, however, argue that all these objections pale in comparison to the enormous advantages of using a single, logical, globally accepted system of measurement—a point that was underscored in 1999 when confusion between metric and English measurements contributed to the failure of the Mars Climate Orbiter space probe, a $125 million NASA project. As of this writing, Liberia, Myanmar, and the United States are the only nations which have not officially adopted the metric system. Among those that have adopted it, enforcement and popular acceptance vary widely; in many places the metric system, though official, is neither compulsory nor much used for everyday purposes. However, it is certainly the dominant system in science, engineering, medicine, and pharmacy, as well as in international commerce and Olympic sports.