:: From the metric system to the international system::
The missions of the Conservatoire Des Arts Et Métiers

The Institute for Metrology and Technology which is attached to the Ministry for Agriculture and Trade, did not have the means necessary to the operations and the studies that comparisons between weights and measures demanded. The government had to create special committees when it was necessary. It resorted to members of the Institute, teachers from the School of Technology and Engineering or technicians.

After the legal obligation came into force in 1840, the government thought it necessary to designate an organism which would be entrusted with this kind of operations, and it chose the School of Technology and Engineering. The School director received a ministerial order in April 1848. It said that "For the sake of science and industry, the central prototype standards repository which is established at the Ministry for Agriculture and Trade will be transferred to the School of Technology and Engineering, and will be placed under the direction and surveillance of the School."

Concerning the exchanges of standards that began in 1841, the order added, concerning checking and comparing that "this task, which was to be executed under the patronage of a Scientific Commission, must be continued under your personal direction." From the following month - May 1848 - the models, standards and instruments that were preserved in the Ministry "Weights and Measures Gallery" were moved to the School of Technology and Engineering.

The School sent a complete collection of weights, measures and weighing instruments to the World Exhibition that took place in London in 1851. It had order the collection to Parent, a mechanic who worked with screw presses. From these times on, the metric system advantages were more and more universally appreciated thanks to the relationships that the 1851, 1855 and 1862 world exhibitions established between scientists and engineers. The comparisons that were demanded to the School were all the more important since it dealt often with standards which were to become national prototypes.

Processes were run with the School's platinum standards. At its request, this standards were subjected to a new comparison with the Archives standards in 1864. Thus, it was possible to work with all the indisputable results from the School operations.

From 1867 to 1869, the School reviewed the standards that depended to the weights and measures checking offices. The 371 offices had got metre, kilogramme and litre standards, adjusted with a one-hundred-thousandth accuracy for lengths and weights, and a ten-thousandth accuracy for capacities, which widely exceeded local needs.

In 1869, when France was to suggest a meeting of an International Commission on measures, fourteen states had received, thanks to the School, standardized metric measures.

The works of the Metre International Commission in 1870 and 1872 took place in the School. They were led by the General Morin, a membre of the Institute and the School's director. Tresca, the assistant director, lent a very active support to these works too. Among others, he developped the X-profile which was adopted for the international metre in 1889.

The School's workshops also tried to melt many platinum-iridium alloys. In may 1874, they got a 250 kg casting of an alloy which was known as "the School's alloy". It was not kept for the international prototypes because it did not respect the allowances regarding the presence of some impurities and because there was too much iridium. It is an alloy made by Johnson-Matthey, from London, that was chosen. However, the national meters that were made of the School's alloy were later considered as stable as the ones made of the London alloy.

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