Beschreibung:

LE ROY, Pierre (1717-1785). Précis des recherches faites en France depuis l'année 1730, pour la détermination des longitudes en mer . Amsterdam: the author, Le Breton, Jombert and Bailly, 1773. -- Suite du précis sur les montres marines de France; avec un supplement au mémoire sur la meilleure maniere de mesurer le tems en mer . Leiden: the author, Le Breton, Jombert and Bailly, 1774. Together 2 works in one, 4 o (240 x 192 mm). Modern boards. FIRST EDITIONS. Le Roy was a prominent clock maker in Paris, whom Louis XV had appointed Royal horologer for the construction of an accurate chronometer for the determination of longitudes of sea. The timekeeper which he had exhibited at Versailles before the King and the Academy of Sciences in 1766 resulted in a possible error in finding longitudes to 1/18th of a degree. These works refute his competitor, Ferdinand Berthoud of Neufchâtel. However excellent Le Roy's chronometers, John Harrison had surpassed them with his "Fifth watch" in London, 1772.