Mesures usuelles
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Mesures usuelles (French for customary measurements) were a system of measurement introduced to act as compromise between metric system and traditional measurements.
The French First Republic established the metric system, but could not provide an education system for all of its citizens to train them unto familiarity and acceptance. Indeed, there was hardly any public communication at the detail required outside the Paris area. Most people could not even buy all the measuring instruments to fully grasp the concepts and use the metric system, anyway, and still thought in terms which were not fully decimal, but had the fractional subdivisions of the previous system: a livre (pound) was thought necessarily to be divided into sixteen onces (ounces); a toise (fathom or double-yard) was thought to be divided into 72 pouces (inches) - as though these were absolute concepts.
Napoleon I, the Emperor of the French, approved of the metric system, but recognized the difficulty of its acceptance among the populace. In 1812 he accepted that for some time the common people could use the subdivisions they preferred, though these would not be based on the royal or provincial units of measurement, but the metric ones. Thus the prototypes of the metric units: the kilogramme and metre served an immediate standardization over the whole country, instead of having several legal types in different parts of the country, let alone across the whole of Europe. The new (but never called "new") livre was accepted as five hundred grammes, the new (but never called "new") toise was accepted as two metres. Products could be sold in shops under the old names, which related to one another in the same manner, but did not have quite the same absolute sizes. The term for this series of measurements was mesures usuelles.
The toise or French fathom, though used more often than an English fathom, was now defined as two metres in length, and was divided into 6 pieds, or "feet"; this French foot (thus being in length a third of a metre) being divided in turn into 12 pouces, or "inches," and, as in Britain but not as in the US, the inch was divided into 12 lignes, or lines.
Another old unit of measuring length, the aune or "ell" used to measure cloth was 120 centimetres, and divided into halves; tiers, meaning "thirds"; and quarters. (This measurement has survived in the form of wood sizes sold in hardware stores throughout Europe, but the name of the basic size, as well as its subdivisions, has been discarded.)
The litre was subdivided like an English quart, into demis (literally, "halves", being the equivalent of a pint of about sixteen fluid ounces), quarts (literally, "fourths", being the equivalent of a cup of about eight fluid ounces), huitièmes (literally, "eighths") and seizièmes (literally, "sixteenths," of about two fluid ounces).
The boisseau, or "bushel," was redefined as an eighth of a hectolitre; it also kept its double, half, and quarter subdivisions.
The livre, or "pound," was restandardized to 500 grams, but was now able to be divided into 16 onces, or "ounces"; each such French ounce had its old subdivision into 8 gros; each gros being thought of as being composed of 72 grains, of which the name is the same as in English. Hence, the livre was of 9216 of these grains.
The system of permitting the usual measures lasted until 1839, even though this was under a constitutional monarchy, rather than either the Empire of Napoleon III or under the Third Republic of France, which would each have had greater ideological interest in getting rid of feudal subdivisions and so present themselves as being progressive.
Similar methods were also used when other countries moved to the metric system. In Germany, a half-kilo is sometimes referred to as a Pfund (pound), while in the People's Republic of China, the Li was redefined from approximately 576 metres to 500m and the Jin was defined as 500 grammes rather than about 605g. This 500g jin is still commonly used in open-air markets in mainland China.
