Famous Watchmakers | XVIII | Pierre Le Roy | Fondation De La Haute Horlogerie

Century

Pierre Le Roy

Pierre Le Roy © MHE

1717-1785
French clockmaker and chronometer maker.
Maître 1737.
Juré 1748.
Son of Julien Le Roy.
The pioneer in chronometry in France (with Ferdinand Berthoud).
His first marine chronometer was tested in 1763.

1748
Invention of a marine chronometer escapement which he described as a spring escapement. This escapement, described in a document that he presented to the Academy of Sciences in 1748, was actually never made. It was imperfect and Pierre Le Roy sought to improve it.

Circa 1750
Invention of the “duplex” escapement (evolution of the cylinder escapement). It was less successful in France than England where it was broadly used between 1790 and 1860.
Improvement of the spiral. Before the discovery of the appropriate length, Pierre Le Roy managed to make the spirals he used isochronous.

1766
Invention of the first self-compensating balance wheel to counter temperature variation effects (with thermometer).
Presented Louis XV with a particularly sophisticated marine chronometer. It was the first to bring together the three essential components of chronometry: spring escapement, self-compensating balance wheel and isochronous spiral.
This took nothing away from John Harrison who remained the first to have made an efficient marine chronometer.
Pierre Le Roy received two awards by the Royal Academy of Sciences for this work (from 1767 to 1769).

1769
Invention of the bi-metallic self-compensating balance wheel. Pierre Le Roy preferred the thermometric balance wheel as the bi-metallic balance wheel had a slight defect in medium temperatures which was solved more than half a century later.