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The Mediterranean of Louis XV 251
paign to chart the coasts of Spain in 1753, during which time he
determined the longitude of Cartagena. In 1757–8 he was at
work on Cyprus. These operations were interrupted by the
Seven Years War but were resumed in 1764 and 1766 when
Chabert undertook two further campaigns to determine the
longitude of sites in Sicily and the North African coast. His
method required that he establish temporary observatories on
land and that his instruments be protected from the elements by
a tent. After establishing local time with a pendulum clock and
determining the precise north–south orientation of a given site,
he spent between six and twenty-four hours observing the course
of the moon and noting the exact time that it passed in front of
individual stars. Returning to Paris, Chabert compared his work
with observations of the same phenomena made by astronomers
in such diverse sites as Vienna and Stockholm, and was thus able
to establish the longitudes of the points he visited. This method
was supplemented by more rudimentary, labour-intensive surveys
of coasts based on the principles of triangulation.
In a paper presented to the Académie des Sciences in 1766,
Chabert forecast the transformation of cartography that would
occur subsequent to the application of reliable spring-driven
marine chronometers to the determination of longitude: ‘Nous
serons toujours forcés de nous contenter d’un très-petit nombre
de déterminations jusqu’au temps où l’exécution des horloges
marines nous fournira des moyens prompts & sûrs de multiplier
les observations de longitude à terre ainsi qu’à la mer.’ 35 Such
chronometers were in fact being tested by British and French
scientists at the time Chabert presented his research to the
Académie des Sciences, and in 1771 he wrote to the Contrôleur
Général Joseph-Marie Terray (1715–78) requesting a chronometer
for his work mapping the Aegean Sea. 36 Chabert
35 J.-B. de Chabert, ‘Mémoire sur l’état actuel de l’entreprise pour la
rectification des Cartes marines de la Méditerranée’, HAS, 1766, Mém.
384–94. Chabert’s work was supported throughout the 1760s by Etienne-
François, duc de Choiseul (1719–75) and his cousin César-Gabriel, duc de
Choiseul-Praslin (1712–85) who served as Secretaries of State for Maritime
Affairs from 1760–6 and from 1766–70 respectively.
36 Chabert to Sartine (July 1775) (Archives Nationales (Paris), Marine G
97, dossier 1, fol. 31). During the public assembly of the Académie des
Sciences on Easter 1783, Chabert read a ‘Mémoire sur l’usage des Horloges
marines, relativement à la Navigation, & sur-tout à la géographie’, HAS,
1783, Mém. 49–66.