Mouchez, Ernest Barthél

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(b. Madrid, Spain, 24 August 1821; d. Wissous, Seine-et-Oise, France, 29 June 1892)

cartography, astronomy.

Mouchez studied at Versailles and then entered the École Navale to prepare for a career in the navy. He became an ensign in 1843, a post captain in 1868, and a rear admiral in 1878. In the meantime he was elected a member of the Bureau des Longitudes (1873) and of the astronomy section of the Académie des Sciences (1875, replacing L. Mathieu), and became director of the Paris observatory (26 June 1878).

As soon as he began his voyages, Mouchez started making important hydrographical studies along the coasts of Korea, China, and South America (sailing 320 kilometers up the Paraguay River). In 1862 he was sent by the minister of the navy to explore the Abrolhos Islands of Brazil, and he then explored 4,000 kilometers of coastline between the Amazon and the Rio de la Plata. From 1867 to 1873 Mouchez charted the coast of Algeria during several expeditions. In all, he published about 140 maps and determined many geographical positions.

From the beginning Mouchez worked to improve surveying techniques and promoted the use by the navy of suitably adapted stationary observational instruments. In particular he employed a meridian telescope designed to determine lunar culminations and generalized the use of the theodolite in topographical surveying. By means of these modifications, he reduced the margin of error in the determination of longitudes from 30″ to 3″ or 4″.

In 1874 Mouchez was sent by the Académie des Sciences to St. Paul Island in the Indian Ocean to observe the transit of Venus on 9 December; he succeeded in making more than 400 extremely sharp exposures. In 1878 he succeeded Le Verrier as director of the Paris observatory. Dissatisfied both with its state of repair and with the quality of the work being done there, he tried in vain to persuade the authorities to build a branch of the observatory outside of Paris, in Versailles or in the forest of Verrières, and to construct lodgings for the staff nearby. Although he failed in this project, Mouchez improved the observatory of the Bureau des Longitudes in the park of Montsouris (at the southern edge of Paris), created a school of practical astronomy at the Paris observatory (1879), and founded the Bulletin astronomique (1884).

Arago had embarked on a program of improving Lalande’s catalog of 50,000 stars with the aid of new, more precise measurements. Mouchez published the part observed up to 1875. Most notably, however, he enlisted the support of Sir David Gill, director of the Cape observatory, to bring about an international astronomical congress at Paris in 1887. It was there decided to produce photographically a large-scale general map of the heavens and to establish a catalog giving the position and brightness of all stars up to the eleventh magnitude. Two young astronomers at the Paris observatory, the brothers Prosper and Paul Henry, both of whom were also talented opticians, had just completed an astrograph and Mouchez had it adopted for this gigantic undertaking, which took more than fifty years. Four French observatories covered nearly half of the northern hemisphere, and eighteen other observatories participated.


I. Original Works. A list of Mouchez’s books and other scientific publications can be found in the Royal Society’s Catalogue of Scientific Papers, IV, 498; VIII, 448; and X, 864; in Poggendorff, III, 940; and IV, 1034–1035; in Catalogue généal des livres imprimés de la Bibliothèque nationale, CXX, cols. 533–538 and in Notice sur les travaux scientifiques de M. Mouchez (Paris, 1875).

On hydrography he wrote Recherches sur la longitude de la côte orientale de l’Amérique du Sud(Paris, 1866); Rio de la Plata. Description et instructions nautiques (Paris, 1873); Instructions nautiques sur les côtes d’Algérie (Paris, 1879); and Instructions nautiques sur les côtes du Brésil (Paris, 1890).

In astronomy, see La photographic astronomique à l’Observatoire de Paris et la Carte du ciel (Paris, 1887); and Rapport annuel de l’observatoire de Paris for 1884–1891 (Paris, 1885–1892). He was also responsible for the publication of vols. 24–39 of Annales de l’Observatoire de Paris.

II. Secondary Literature. Besides the Notice sur les travaux scientifiques de M. Mouchez (Paris, 1875), written at the time of his candidacy for the Académie des Sciences, there are only a few brief biographies: that in the Dictionnaire universel des contemporains, G. Vapereau, ed., 5th ed. (Paris, 1880), 1323; that in Polybiblion, 2nd ser., 36 (July–Dec. 1892), 78; the pamphlet containing the speeches given at his funeral (Paris, 1892); and an address delivered by B. Baillaud at the unveiling of his statue at Le Havre in 1921 (Paris, 1921).

Juliette Taton