Juan Y Santacilla, Jorge

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Juan Y Santacilla, Jorge

(b. Novelda, Alicante, Spain, 5 January 1713; d. Madrid, Spain, 21 July 1773)


Juan’s parents, Bernardo Juan y Cancia and Violante Santacilla y Soler, were hidalgos, the lower aristocracy. Orphaned at the age of three, he first attended school in Zaragoza and at the age of twelve went to Malta, where he joined the Knights of Malta with the rank of commander of Gracia de Aliaga. At seventeen he enlisted as a midshipman at the Compañia of Càdiz, where he completed his higher studies. His comrades nicknamed him “Euclid” because of his aptitude for the exact sciences. He took part in various privateering campaigns against the Moors and in the expedition against Oran. Juan never married.

After Cassini’s measurements of the meridians seemed to show that the earth was a spheroid elongated at the poles, in clear opposition to Newton’s theory, the French Academy of Sciences proposed that two series of measurements of one degree of an arc of meridian should be made, one near the North Pole, the other near the equator. Louis XV designated a Hispano-French commission for the measurement at the equator, in which, by appointment of Philip V, Juan and Antonio de Ulloa would participate, on behalf of Spain, with La Condamine, Godin, Bouguer, and Joseph de Jussieu.

In 1736 the commission’s expedition began its work, principally in the regions of Quito and Guayaquil. Complementary scientific observations were made of the speed of sound and of various aspects of astronomy, physics, geography, biology, and geology. Great effort went into achieving precision and accuracy for the measurements of the Peruvian meridian. The measurement made by the French members of the expedition gave a longitude of 56, 750 toises, while that of the Spaniards gave 56, 758; that is, a minor difference on the order of 14:100,000. These measurements confirmed the Newtonian theory of the shape of the earth and were extraordinary for their precision.

In 1745, nine years after the inception of the expedition, Juan and his colleague Ulloa returned to Spain, each taking a different route as a precaution for safe arrival of the data.

Juan subsequently designed and directed the shipyards at El Ferrol and La Carraca, took part in the improvement of the working and development of the mines of Almadén, founded the astronomical observatory of Càdiz, and carried out several diplomatic and special missions. He was squadron commander of the Royal Armada and director, at the age of fifty-seven, of the Royal Seminary of Nobles. During his captaincy of the company of midshipmen of Càdiz he established, in his house there, the Friendly Literary Society, which is considered the forerunner of the Royal Society of Sciences of Madrid. For several years this group met each Thursday to consider questions of mathematics, physics, geography, hygiene, history, and archaeology.

His combination of theoretical learning and practical experience enabled Juan, in his Examen maritimo, to provide a considerable base for the improvements of naval science, to refute several empirical theories of navigation, and to establish the fundamental principles of naval architecture. The book is a valuable application of mechanics to naval science.

Among the societies in which Juan held membership were the Royal Society, the French Academy of Sciences, the Royal Academy of Sciences of Berlin, and the Spanish Academy of San Fernando.


I. Original Works. Juan y Santacilla’s writings are Relación histórica del viaje a América meridional. . ., 4 vols. (Madrid, 1747), written with Antonio de Ulloa—vol. II, para. 1,026 tells of the discovery of platinum by the Spaniards in Peru; Disertación histórica y geogràfica sobre el meridiano de demaracación entre los dominios de Espana y Portugal y los parajes por donde pasa en la América meridional . . .(Madrid, 1749), written with Ulloa; and Examen maritimo teórico pràctico. . .(Madrid, 1771, 1793), translated into English (London, 1784) and French (Nantes, 1783; Paris, 1793), aslo republished in Spanish (Madrid, 1968).

See also “Reglamento para la construcctión de lonas” (1751), MS in the collection of Vargas Ponce; Compendio de navegación para el uso de los Caballeros Guardiasmarinas (Cadiz, 1757); “Informe a S. M. sobre los perjuicios de la construcciòn francesa de los bajeles” (1773), MS;Observaciones astronómicas y fichas hechas por O. de S. M. en los reinos del peru (Madrid, 1773, 1778), written with Ulloa.

Other works are Estado de la astronomia en Europa . . .(Madrid, 1773); “Reflexiones sobre la fàbrica y uso del cuarto-de-circulo” (Dirección de Hidrografia, 1809); “Las observaciones del paso de Venus por el disco del sol (Memoir Deposito Hidrografico, 1809); “Metodo de levantar o dirigir el mapa o plano general de España (Memoir Deposito Hidrografico, 1809); Noticias secretas de América sobre el estado moral y politlco de los reinos del Perú y provincias de Quito, cosas de Nueva Granada y Chile . . . (London, 1826), written with Ulloa; and “Relox o crònometro inventado pro Juan Harrison.

A fair number of Juan’s notes and papers on cosmography and navigation exist, the majority of them unpublished. Among these are two volumes with ten blueprints for naval construction.

II. Secondary Literature. See Diccionario enciclopédico hispano-americano, XI (Barcelona, 1892), 217; Francis co Cervera y Jimenénez Alfaro, Jorge Juan y la colonización española en America...(Madrid, 1927).

J. M. LÓpez DE Azcona

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