Made to Measure — Delambre and Borda and the Invention of the Metre
Two hundred thirty years ago, leaders of the French Revolution faced an urgent challenge — how to get people to work together to solve the desperate problems facing their divided country? The leaders understood that building the trust necessary for cooperation and innovation required setting standards that are universal and impartial. This was so important that they set the country’s best minds to the task, and they inscribed the results in stone for all to see.
In 1791, the government turned to scientists of the former Royal Academy of Science to establish new units for measuring length (metre), weight (gram) and volume (litre). The new standards signaled a clean break from the corrupt practices of the overthrown monarchy. And, replacing a myriad of provincial standards with a uniform system that applied throughout France promoted wider cooperation and trust and that expanded the national economy. A merchant in Paris could order a quantity of goods from Lyon confident that confusion over the units of measure would not leave him short changed.
The new measurement standards, which became the present-day metric system, would be free of any possible source of bias because they would be taken from nature. The length of the meter was set as 1/10,000,000 the distance between the North Pole and the Equator measured along a line of longitude, a meridian. Jean Baptiste Joseph Delambre led a team of scientists charged with establishing this distance by precisely measuring the length from Dunkirk to Barcelona along the meridian that passes through Paris and the Paris Observatory. Delambre split this task with Pierre Méchain. Delambre measured the meridian from Dunkirk south to Rodez, a town about 110 km northeast of Toulouse, and Méchain completed the survey from Rodez through the Pyrenees to Barcelona. This survey required 6 years to complete, 1792–1798.
With the prestige of the Academy and France on the line, this had to be the most accurate geodesic survey ever made. The teams had the advantage of the most advanced instruments, produced for this task by Jean-Charles de Borda. However, as both Delambre and Méchain were aware, it is in the nature of fieldwork that errors of measurement will inevitably occur, and they accumulate over time. The pressure of constant vigilance against unavoidable error drove Méchain mad. In the end, it fell to the more resilient, and politically astute, Delambre to perform the final calculations that first established the length of the metre.
Jean Baptiste Joseph Delambre, astronomer, and Jean-Charles de Borda, mathematician, are two of the 72 scientists and engineers named on the Eiffel Tower.
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“Static meters (provisional) are placed in public public places between February 1796 and December 1797. They will be designed by Chalgrin (the future architect of the Arc de Triomphe) and manufactured by the sculptor — Corbel marblemaker. These meters therefore refer to the measurements of the Meridian made previously by Nicolas Louis de la Caille: there are still two marble meters in Paris visible on the 16 installed, 36 rue Vaugirard and 13 place Vendome. Others in iron are visible in Lyon (inner courtyard of the Town Hall), Agde (entrance to the old town hall), Montauban (pillar of the National Square), Marvejols (wall of the old Halle).” — from https://archives.entreprises.gouv.fr/2012/www.industrie.gouv.fr/metro/aquoisert/metre.html
