Very fine example of a French pocket chronometer made by a pupil of Auguste Louis Berthoud, Louis Berthoud's grandson and nephew of Henri Motel. The extremely fine Louis Berthoud pivoted detent escapement, usually set between plates, is clearly visible in this piece.This chronometer is almost identical to the pocket chronometer No. 271 by Henri Motel. Both chronometers are described and illustrated in: J.-C. Sabrier: La Longitude en mer à l'heure de Louis Berthoud et de Henri Motel, Antiquorum Editions, Geneva, 1993, p. 622, fig. 169 and 170.Onésime Dumas (1824-1889). Dumas was Louis Berthoud's grandson and the nephew of Henri Motel. He was placed by the Government, in 1837, as pupil to Louis-Frédéric Perrelet then in charge of the Ecole des Horlogers de la Marine, since 1832. When Perrelet for health reasons had to resign in December 1839, and Charles-Auguste Berthoud was appointed as his successor by the Ministre de la Marine to complete the instruction of his pupils, Onésime Dumas had already two and half years of apprenticeship.When he left the school, he worked for a short period with Motel. Therefore, the very first chronometers made by Onésime Dumas, were very similar to those produced by Louis Berthoud and later by his two sons. Then, working with his uncle, he made few chronometers with the highly refined calibre which ensured the fame of Henri Motel. He then succeeded to Gannery in Saint-Nicolas d'Aliermont, in 1851. The chronometer No. 421, produced the same year, carries both their signatures. He employed betwen 12 and 15 craftsmen and exhibited precision horology at Rouen in 1856. He used to sign: Dumas Successeur de Gannery. He left his name to a new full plate caliber, very much inspired by the English style, not as elegant nor refined as that of Motel, but less expensive to produce, robust and reliable, which was more or less adopted by all the other French makers.Literature:J.-C. Sabrier: La Longitude en Mer à l'Heure de Louis Berthoud et Henri Motel, Antiquorum Editions, Genève 1993.