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Heritage classified

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Origin and history

The former astronomical observatory of the Nantes Navy, built in the early 19th century, is part of a school set dedicated to hydrography, active from 1827 to 1887. Located on Rue Flanders-Dunkerque-40, this building stands out for its 27-metre tower, designed for teaching astronomical navigation and setting marine chronometers. Its architecture, including anti-vibration vaults, reflects engineering adapted to the scientific needs of the time.

The construction was decided in 1825 by the Minister of Marine, Christophe de Chabrol de Crouzol, as part of a reform of the hydrography schools under Charles X. Nantes, classified among the major ports, must have an observatory and a public classroom. The architect Étienne Blon proposes a project on his own land, rented for 60 years, with funding shared between the state, the city and private partners. Inaugurated in 1827, the building also houses a labour exchange (1893) and a cinema (1913-1960s).

The tower, used for astronomical and meteorological observations, hosts a meridian bezel and a Berthoud regulator. Its watch cabinet, on the 4th floor, allows to calibrate navigation instruments. After the school was closed in 1887, the site was purchased by the Savings Bank. Rediscovered in the 20th century by Olivier Sauzereau, the observatory was listed as a historic monument in 2013 for its uniqueness. Today inaccessible, it opens exceptionally at heritage events.

The choice of its location, on a height without vis-à-vis, met the scientific requirements of visibility and stability. Flanders-Dunkerque-40, then on the urban periphery, benefited from accelerated developments to serve the site. Close to the harbour facilities, the tower symbolized the link between the city, the merchant navy and the technical advances of the time.

Among the notable events, the observatory studied the solar ring eclipse of 1836, described by Jean-Marie Bachelot de La Pylaie. Hydrography students learned to master astronomical navigation tools, which are essential for long voyages. The broken arch vaults of the upper floors, designed as shock absorbers, illustrate architectural innovation in the service of instrumental precision.

After its scientific decommissioning, the building experienced various uses: place of worker training (public courses in geometry and mechanics), labour exchange, and then cinema. These changes reflect the adaptation of the Nantes heritage to successive social and cultural needs. The Meridian association works today for its preservation and valorisation, highlighting its role in local scientific history.

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