Jorge Juan y Santacilia | |
|---|---|
 Portrait by Rafael Tegeo | |
| Born | 5 January 1713 Novelda, Spain |
| Died | 21 June 1773 (aged 60) Madrid, Spain |
| Nationality | Spanish |
| Alma mater | Royal Company of Marine Guards |
| Known for | Figure of the earth |
| Scientific career | |
| Fields | Geodesy, Naval architecture, Astronomy, Mathematics |
| Institutions | Spanish Navy, Seminary of Nobles of Madrid |
| Military service | |
| Allegiance |  Order of Saint John  Kingdom of Spain |
| Branch/service | Maltese Navy (1725–29) Spanish Navy (1730–73) |
| Rank | Captain |
| Battles/wars | Conquest of Oran, Battle of Bitonto, War of Jenkins' Ear |
Jorge Juan y Santacilia (Novelda, Alicante, 5 January 1713 – Madrid, 21 June 1773) was a Spanish mariner, mathematician, natural scientist, astronomer, engineer, and educator. He is generally regarded as one of the most important scientific figures of the Enlightenment in Spain. As a military officer, he undertook sensitive diplomatic missions for the Spanish crown and contributed to the modernization and professionalization of the Spanish Navy. In his lifetime, he came to be known as el sabio español ("the Spanish savant"). His career as a public servant constitutes an important chapter in the Bourbon Reforms of the 18th century.
As a young naval lieutenant, Juan participated in the French Geodesic Mission to the Equator of 1735–1744, which established definitively that the shape of the Earth is an oblate spheroid, flattened at the poles, as predicted in Isaac Newton's Principia. With his fellow lieutenant Antonio de Ulloa, Juan travelled widely in the territories of the Viceroyalty of Peru and made detailed scientific, military, and political observations of the region. They also helped to organize the defense of the Peruvian coast against the English squadron of Commodore Anson, after the outbreak of the War of Jenkins' Ear in 1739.
After returning to Spain in 1746, Juan became a protégé and collaborator of the Marquess of Ensenada, a leading minister under King Ferdinand VI. Under Ensenada's orders, Juan undertook an eighteen-month mission of industrial espionage in London, after which he worked tirelessly to modernize and professionalize naval architecture and other operations in Spain. Juan's influence declined somewhat after Ensenada fell from power in 1754. In 1760 Juan was appointed as Squadron Commander, the most senior officer in the Spanish Navy, but ill health soon forced him to give up that role and instead take up diplomatic and educational missions.
As a mathematician and educator, Juan promoted the study and application of the infinitesimal calculus at a time when the subject was not taught in Spanish universities. He served as ambassador plenipotentiary to the Sultan of Morocco in 1766–1767, and as director of the Seminary of Nobles of Madrid from 1770 until his death in 1773.