December 10, 1799: bicentenary of the decimal Metric system


The Observatoire de Paris was founded in 1667, at the request of the very new Academy of Science. The founder act was to trace the meridian line of Paris (June 21 1667) on which was built, symmetrically, the Perrault building. This meridian line became the reference for the control of the astronomical observations and the meridian line origin for the determination of longitudes. It marked also the beginning of the monitoring and the conservation of time, related to the rotation of the Earth, by the astronomers of the Observatoire de Paris.

A hundred years later, the meridian line of Paris was going to play another great role while being used as a basis for the establishment of the " decimal Metric system "

1789: a claim returned regularly in the registers of grievances: it was wished that it existed only one measurement for all the kingdom.

1791: the Assembly adopts " the size of the terrestrial quarter of meridian line for base of the new system of measurement ". Thus, the ten millionth part of this arc becomes the unit of length, the meter.

It will be the base of a system of measurement, officially called " revolutionary measures ". Those will not be independent from each other, but bound by the meter and the system will be decimal: the volume and units of area are respectively the square and the cube of the meter; the unit of weight, the kilogramme depends on the meter, since it is the weight of one cubic decimetre of water.

1792: the astronomers Jean-Baptiste Delambre and Pierre Méchain begin the measurement of an arc of the meridian line of Paris between Dunkirk and Barcelona. The operation will be finished only in 1798. Meanwhile, in 1795, Convention founds one provisional meter.

1799: the law of December 10, 1799 (19 frimaire year VIII) defines the meter.

From this vast undertaking was born the decimal Metric system, which, made compulsory to France as from 1840, knew to be essential after many obstacles and forms today integral part of the everyday life of the men of more than 130 countries.

Paris, November 25, 1999.