Pierre Le Roy

Pierre Le Roy (* 1717 in Paris, † 1785 in Vitry -sur -Seine ) was one of the leading French watchmaker and inventor. Together with Ferdinand Berthoud Le Roy was a leader in the development of the chronometer escapements. He created a temperature compensation by a bimetallic balance with adjustable mass screws and the isochronous balance spring. His developments laid the foundation for today's mechanical chronometer.

Le Roy was born in Paris, the son of Julien Le Roy (1686-1759), which official watchmaker of Louis XV. was and had worked with Henry Sully.

Invention of the chronometer escapement

In 1748 Le Roy invented already a first form of the free inhibition. He made next chronometer also stop watches, but are his greatest successes in the construction of marine chronometers. As John Harrison, he worked on improving the seaworthiness of marine chronometers, which he achieved by a decoupling of escapement and balance wheel. He also first introduced the use of bimetallic tires for the balance. His method of temperature compensation allowed the variation of the transition without changing the length of the spiral, as he had found that an isochronous balance spring has only one optimal length, which he therefore did not want to change. This length is characterized by an independence of the frequency of the amplitude, making mechanical watches run smoothly, regardless of the varying drive through the barrel.

Development of modern marine chronometer

After the first draft in 1754, Le Roy in 1756 built his first chronometer. The technical development of his chronometer he continued until 1766, when he constructed a clock with open escapement, temperature-compensated balance and the isochronous balance spring, which today forms the basis of mechanical marine chronometers. The accuracy was comparable to that of H4 chronometer by John Harrison.

In 1769 Le Roy won the double prize of the French Academy for the best method to measure at sea time. This success was based in part on the isochronous balance spring, for which he was with Ferdinand Berthoud in the competition, Le Roy, however, was first published. He was also skilled the author of several writings on the art of watchmaking and chronographs, including Etrennes chronométriques of 1760, and was also in 1760 royal watchmaker.

His work has been in France but less valued than those of his contemporaries Ferdinand Berthoud, which was awarded the title Watchmaker de Marine ( Navy watchmaker ). Le Roy then went into retirement.

Pictures

Le Roy chronometer escapement

Pierre Le Roy chronometer, 1766, Musée des Arts et Métiers

Construction plan of Le Roy chronometer