BERTHOUD (Futuna:in), Chronometer-maker to the French Admiralty, member of the Institute of France, and of the Legion of Honour, was born in the county of Neufchatel in 1727. His father's profession was that of architect, and the son was in tended to be bred to the church, but, having shown a taste for clock-work, an experienced workman in that art was got to instruct him in • its principles, and young Berthoud was afterwards sent to Paris to improve in the knowledge and practice of the art he had thus commenced. He settled in Paris in 1745, and applied himself to the making of chrono meters, an art which was then in its infancy. A chronometer is an accurately made watch, whose chief peculiarity consists in a piece of mechanism intended to render the number of vibrations of the balance equal in equal times, at all the degrees of temperature to which the instrument is exposed; and the chronometer being a portable instrument, which can be used on ship-board, is by this mechanism made to move at a constant rate;—say at the rate of mean solar time, so that it shows what hour it is at meridian of Greenwich, if the chronometer, at the commencement of the voyage, was set to Green wich time, whilst the observation of the height of the sun or of a star gives the hour, angle, and the 'hour at the Owe where the ship is: the difference between these two• times is the longitude of the 'ship. Fleurieu and Borda, by order of the French Government, made a voyage from La Rochelle to the West Indies and Newfoundland, for the pur pose of trying the chronometers of Ferdinand Ber thoud, and found that they gave the longitude with only a quarter of a degree of longitude of error, after a cruize of six weeks. Satisfactory results were also obtained from his chronometers in the expedition of Verdun, Borda, and Pingre, which was appointed to try them, together with those of Le Roy. An ac
count of this expedition is published.
Sully, an English watch-maker established in Pa ris, was the first who, in that city, attempted the construction of chronometers for finding the longi. tude ; this he did in 1724. In 1736, the chronome ters of the English artist, Harrison, were tried at sea. In France there were no chronometer-makere of note, from the first attempts of Sully, till Pierre le Roy and Ferdinand Berthoud, betwee6 wham there was some discussion about the priority of their discoveries and improvements. Ferdinand Berthoud's chronometers were long the most esteemed of any in France. Louis Berthoud, the nephew and suc cessor of Ferdinand, has improved upon the ma chines of his uncle, and has made them generally of a smaller size, so as to become more portable. And many farther improvements have been made by the English chronometer-makers.
Ferdinand Berthoud was regular in his habits of life ; he retained the use of his faculties to the last ; and died, of hydrythorax, at his country-house, is the Valley of Montmorency, in 1807, having attain ed the age of 80. The principal published works of Ferdinand Berthoud are, Essai sur 1786. 2-vols. in 4to ; two Tracts on Chronometers, 1173 ; De In Mesure du Temps, 1787, in 4to; Les Longitudes par la Mesure du Temps, 1775, in 4to; a Tract on Chronometers, 1782, in 4to ; Histoire de la Mesure du Temps par lea Horloges, 1802, 2 vols. in 4to; C Art de conduire et de r‘gler les Pend des, d les Montres, 1760, in 12me. In this tract directions are given for regulating clocks and watches suited to general readers; it has gone-through several edi• Lions. (v.)