TESTING BERTHOUD'S CHRONOMETER.

FLEURIEU, (CHALES PIERRE CLARET de).

Voyage fait par Ordre du Roi en 1768 et 1769, à différentes Parties du Monde, Pour éprouver en mer les Horloges Marines inventées par M. Ferdinand Berthoud. Première partie, Contenant 1. Le Journal des Horloges Marines, ou la suite de quatorze vérifications servant à apprécier la régularité de ces machines sous différens points de vue, relativement aux divers usages auxquels on peut les employer. 2. Le Journal de la Navigation, dans lequel sont exposés tous les secours que les Horloges ont fournis pour assurer la Navigation & perfectionner la Géographie : d’où suit un examen critique de plusieurs Cartes publiées au Dépôt des plans & journaux de la Marine ; avec une Carte générale de l’Océan Occidental, & des Cartes particulières des îles Canaries, du Cap-vert & des Acores, dresses sur de nouvelles observations. Seconde Partie, contenant Le recueil des Observations Astronomiques.... 2. Un Appendice... instructions sur la maniere d'employer les Horloges Marines....

Paris, Imprimerie Royale, 1773. 4to. 2 nice contemp. full mottled calf. 5 raised bands. Richly gilt spines, tome-and titlelabels with gilt lettering. Neat repairs to top of spines. Stamps on title-pages. Corners a bit bumped. (4),LXXIX,803;(4),622 pp., 5 folded engraved maps, 1 engraved plate and 5 folded tables. Light browning to a few quires. Lower right corners on the last 3 leaves in volume 1 with a mild foxing.

First edition of this splendid work, in which the observations from the testing of Berthaud's marine chronometer were presented for the first time.

Fleurieu took part in a one-year sea campaign to test Berthoud's first marine chronometer, in an attempt to beat Britain in the race to find a reliable way to calculate longitude. The chronometers he thus refined with Ferdinand Berthoud for their later experiments, were the object of major struggles with the king's horologer, Pierre Le Roy. Finally, Claret de Fleurieu and Berthoud were entrusted with the task, setting out on the testing expedition from autumn 1768 to 11 October 1769 on the frigate Isis under Fleurieu's command. The chronometers almost invariably indicated the hour as accurately after the ship had left port, as if they were still on land. Knowing the actual local time at each present location by astronomy, they could easily determine the ship's exact position and longitude on a chart. The results of their observations were published in 1773 under the title Voyage fait par ordre du roi, pour éprouver les horloges marines ("Voyage made by order of the king, to test marine chronometers").

Sabin, 24750.

Order-nr.: 53601