Voyage fait par ordre du roi en 1768, pour éprouver les montres marines inventées par M. le Roy, avec le mémoire sur la meilleure manière de mesurer le tems en mer, qui a remporté le prix double au jugement de l'Académie Royale des Sciences. Contenant la description de la montre à longitudes, présentée à sa majesté le 5 août 1766 (1770). Jean Dominique Cassini, Pierre Le Roy.

Voyage fait par ordre du roi en 1768, pour éprouver les montres marines inventées par M. le Roy, avec le mémoire sur la meilleure manière de mesurer le tems en mer, qui a remporté le prix double au jugement de l'Académie Royale des Sciences. Contenant la description de la montre à longitudes, présentée à sa majesté le 5 août 1766 (1770)

Paris: Charles-Antoine Jombert, 1770. 1st Edition. FIRST EDITION OF A VOYAGE BY CASSINI TO TEST THE NEW MARINE CLOCK – CHRONOMETER -- OF PIERRE LE ROY. Le Roy's chronometer superceded one by John Harrison that had been used for many years. Le Roy’s invention – as Cassini’s report makes clear -- became the most accurate sea chronometer and was described by Rupert T. Gould of the British Royal Navy as the first modern chronometer. Notably, this book bears the bookplate of Commodore F. H. Kjolsen, a Danish naval officer engaged in WW II and who went on to be the Danish naval attache in Washington. The commodore took part in blowing up and sinking the Danish fleet in Copenhagen in 1940 to prevent its falling into enemy hands. At that time he was seized and placed in a German prison camp. Two months later he escaped and sailed to Sweden in a fishing boat with his wife and three children.

John Harrison, an English self-educated carpenter and clock maker, invented the first practical marine chronometer, which enabled navigators to compute accurately their longitude at sea. Harrison’s invention revolutionized the problem of longitude at sea; still, Harrison spent 31 years of experimenting, testing, and fine-tuning an invention that had already revolutionized navigation and enabled the Age of Discovery and Colonialism to accelerate.

In 1766, Pierre Le Roy, watchmaker to King Louis XV, constructed his own chronometer. Though Le Roy had championed Harrison’s invention, his own differed from Harrison’s in a number of significant ways. Le Roy’s chronometer incorporated a detached escapement, something he invented in 1748. This type of escapement incorporated “a temperature-compensated balance and an isochronous balance spring, innovations which would be adopted in subsequent chronometers” (Wikipedia).

Le Roy presented his invention to the Royal Academy and proposed that it be tested. Undertaken at his own expense along the coasts of France and Holland, Le Roy’s chronometer performed admirably. The members of the academy, ready to reward Le Roy a prize and disseminate this invention, decided that it should be submitted to a longer voyage. The Minister of the Navy, M. de Praslin, ordered and financed an expedition to be led by Jean Dominique Cassini. Traveling to to the island Saint-Pierre and to the coasts of Africa and Spain, this work is Cassini’s report of that voyage – a meticulous accounting of the testing of Le Roy’s chronometer.

In 1769 Le Roy was awarded the double prize offered by the French Academy for the invention of the best method of measuring time at sea. Le Roy’s detached escapement created the most accurate regularity at sea, further enabling the 18th centuries’ Age of Discovery. In 1766, Pierre Le Roy, watchmaker to King Louis XV, constructed his own chronometer. Though Le Roy had championed Harrison’s invention, his own differed from Harrison’s in a number of significant ways. Le Roy’s chronometer incorporated a detached escapement, something he invented in 1748. This type of escapement incorporated “a temperature-compensated balance and an isochronous balance spring, innovations which would be adopted in subsequent chronometers” (Wikipedia). Item #1309

CONDITION & DETAILS: Paris, Charles-Antoine Jombert, 1770. 4to (264 x 210 mm.) Stamp on title-page. Provenance: see details in the beginning of this description. iv pp., Vii pp., 144 pp., Xxiv pp., 60 pp., (2) ff. Bound in full mottled calf with 5 raised bands at the spine, each compartment gilt-tooled. The binding is tight and very solid; minor scuffing at the edges. Gilt lettered at the spine. Marbled endpapers. Wide margins within. Internally clean and bright.

Price: $5,000.00