Plate placed in the tower where it ended the meridian of Dunkerque and where it was made ??the first measurement of the meridian. The plaque commemorates the 200th anniversary of the first measurement.
On the plate can be read: "Des dáquesta torre lástronom Pierre Mechan durant els anys 1792-1793 establi els cooedenades de Barcelona e la triangulació per al mesurament de l'arc de meridià que serví de base del sistema mètric decimal.
II cenenari del mesurament del meridià de Dunkerque a Barcelona.
Ajuntament de Barcelona""From this tower the astronomer Pierre Mechan during the years 1792-1793 set cooedenades of Barcelona and the triangulation to measure the arc of the meridian as the basis of the decimal metric system.
Second centenary of the measurement of the meridian from Dunkerque to Barcelona.
Barcelona City Council"
"The Rapport sur le choix d'une unité de mesure outlined a plan to realize the new system of measures. One of the items of the plan was to re-measure the Lacaille-Cassini arc of the Paris meridian from Dunkerque to Perpignan,32also extending the measurements down to Barcelona (a total of almost ten degrees in longitude, for a length of 1075 km..
The campaign of measurements started immediately, apart from delays of practical nature, after the Academy's proposal was accepted. A quote is in order to report the driving spirit of the commission, that also shows the yearning for an `egalité of measures', one of the political and ideological requirements of the new régime that can't be set aside any longer.
There is no need, in our judgment, to await the concurrence of other nations either to choose a unit of measurement or to begin our operations. Indeed, we have eliminated all arbitrariness from this determination and rely only on information equally accessible to all nations.
Two astronomers were nominated responsible of the mission: Jean Baptiste Joseph Delambre, in charge of the northern part of the arc, up to Dunkerque, a French town on the North Sea, close to the Belgian border; Pierre François André Méchain, in charge of the southern part.
In principle, the task was simpler than that accomplished by Lacaille and Cassini fifty years earlier, because it seemed initially possible to use much of their work (like the triangulation stations). However, things were much more difficult, complicated by Revolution and wars. It was almost a miracle that Delambre and Méchain could meet again in Paris in November 1798 alive and with the logbooks of their measurements.
The unexpected long duration of the mission was the reason the académiciens were urged to provide the provisional length of the meter in 1793. In fact, ``the interests of the Republic and of the commerce, the operations initiated on the money and on the cadastre of France, require that the adoption of the new system of weight and measures is not delayed any longer''. The Decimal Metric System was later established by law on April 7, 1795, well before the meridian mission was accomplished.
After the end of the meridian mission an international commission was convened to review the Delambre-Méchain data and to establish the length of the meter. In March 1799 the meter was determined in 443.296 lignes, also taking into account Earth flattening.33The new standard differed by 0.114 lignes (0.32 mm) from the provisional unit. Compared with our present value (see Table 3) one can see that the new result slightly worsened the knowledge of the meridian.34
The manufacture of the definitive model, based on the results on those measurements, was completed in June 1799. On 22 June, the prototype of the meter was solemnly presented to the Council of Elders and of the Five Hundred."
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