Jorge Gaspar Juan y Santacilia (5 January 1713 – 21 June 1773) was a Spanish naval officer, mathematician, scientist, astronomer and engineer. 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 British squadron of George 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.
Family and education
Jorge Juan was born of two distinguished hidalgo families: his father was don Bernardo Juan y Canicia, a relative of the Counts of Peñalba, while his mother was doña Violante Santacilia y Soler de Cornellá, who came from a prominent land-owning family in Elche. Both of his parents were widowed and had several children from their respective first marriages. Jorge Juan was born on 5 January 1713 in a home in the estate El Fondonet (also known, in Castilian, as El Hondón), owned by his grandfather don Cipriano Juan Vergara and located in Novelda, a town in the province of Alicante. He was baptised four days later in the parish church of the neighboring town of Monforte (now known as "Monforte del Cid"). The family lived in a home on the Plaza del Mar in the city of Alicante and vacationed in Novelda.
As a younger son, Jorge was not expected to inherit his father's estate. His family therefore intended him for a career in the military or the church, as was customary for younger sons of noble families. In fact, Jorge had been baptized in the parish of Monforte, rather than that of Novelda (his actual place of birth) in order to render him eligible for a benefice attached to the Collegiate Church of Saint Nicholas, in Alicante, should he eventually pursue an ecclesiastical career. His paternal uncle Antonio Juan was a canon of that church. At the time Monforte, but not Novelda, was considered to lie within the boundaries of the city of Alicante, and the statutes of the Collegiate Church of Saint Nicholas reserved its canonries to natives of Alicante.
His father Bernardo died when Jorge was only two years old. Jorge received his first education at the Jesuit school in Alicante, under the supervision of his uncle, the priest Antonio Juan. Another of Jorge's paternal uncles, Cipriano Juan, was the bailiff of Caspe in the Order of Malta (also known as the "Order of Saint John", or the "Knights Hospitaller"). Cipriano eventually took charge of the education of the young Jorge, sending him to study grammar in Zaragoza as preparation for higher education.
Knight of Malta
In 1725 Cipriano sent his nephew Jorge, aged twelve, to the island of Malta, where he served as page to António Manoel de Vilhena, the Grand Master of the Order of Malta. At the age of thirteen, Jorge was admitted as a member of that Order. This required him to show that all four of his grandparents were of noble birth, by proving their armigerous status and "purity of blood".
"Hospitaller Malta" was at that time a vassal state of the Kingdom of Sicily, ruled by Habsburg emperor Charles VI. Juan stayed in Malta for nearly four years. There he took religious vows as a Knight of Saint John, which imposed upon him the requirement of lifelong celibacy. He also began his naval training by sailing in warships of the Order's navy.
Pope Benedict XIII presented Grand Master Vilhena with the blessed sword and hat in 1724, in recognition of his contribution to the Order of Malta's fight against the Barbary corsairs. Those artifacts were blessed in St. Peter's Basilica, in Rome, on Christmas Eve 1724 and then dispatched to Malta, where they arrived on 3 May 1725. A painting by Maltese artist Enrico Regnaud shows Vilhena as Grand Master, with the sword and hat, accompanied by two pages. These dates have led historians to infer that one of the pages depicted in the painting, who holds the blessed sword along and a shield decorated with the Grand Master's coat of arms, is probably a young Jorge Juan. The painting, which is in the collection of the Grandmaster's Palace in Valletta, was loaned to the Naval Museum of Madrid in 2023–2024 for an exhibit dedicated to the life and legacy of Jorge Juan.
In 1729, aged sixteen, Juan received from the Grand Master the title of Commander of Aliaga (Comendador de Aliaga), a rank that he held for the rest of his life and which provided him with a benefice. Juan left Malta soon thereafter to pursue a naval career in Spain.
Spanish navy
Juan applied for admission to the Royal Company of Marine Guards, the Spanish naval academy, located in the port city of Cádiz. He entered the academy in 1730 and proceeded to study modern technical and scientific studies subjects such as geometry, trigonometry, astronomy, navigation, hydrography, and cartography. He also completed his education in the humanities with lessons in drawing, music, and dancing. He earned a reputation as a brilliant student and his fellow students nicknamed him "Euclid".
As a naval cadet (guardia marina), Juan participated in the successful expedition against Oran of 1732. He finished his studies at the academy in 1734 and took part in the Battle of Bitonto against the Austrians in the Kingdom of Naples. Juan would remain in the service of the Spanish Navy (the Armada) for the rest of his life.
Sojourn in South America
In light of the long-running debate between Cartesians and Newtonians over the figure of the Earth, the French Academy of Sciences decided to sponsor two geodesic expeditions: one to measure the arc length corresponding to one degree of latitude near the equator, and the other to carry out a similar measurement near the Arctic Circle. The only feasible location for the equatorial expedition was in the territory of the Audiencia of Quito, in what is now the country of Ecuador. At the time, this was part of the Viceroyalty of Peru under the Spanish Crown.
In 1734, King Philip V of Spain agreed to allow the French expedition to carry out its work in Quito, under the condition that the French scientists should be joined by two Spanish naval officers capable of understanding and collaborating with the scientific work involved. Upon the recommendation of his First Secretary of State José Patiño, Philip appointed to that role Jorge Juan and Antonio de Ulloa, who were then 21 and 18 years old, respectively. The two were promoted to the rank of naval lieutenant (teniente de navío) so that they would have the appropriate seniority for the mission.
The equatorial expedition was led by three members of the French Academy of Sciences: the astronomer Louis Godin, and geographers Charles Marie de La Condamine and Pierre Bouguer. Their collaborators included the physician and naturalist Joseph de Jussieu and the engineer Jean-Joseph Verguin. On 26 May 1735, Juan and Ulloa left Cádiz in the company of the Marquess of Villagarcía, who had been appointed as the new Viceroy of Peru. They met the French scientists at the Caribbean port of Cartagena de Indias, on the mainland of South America. They then sailed together to Portobelo, crossed the Isthmus of Panama, and proceeded by boat to the Pacific port of Guayaquil. Juan and Ulloa then traveled inland with Godin, reaching the city of Quito in May of 1736.
The Arctic expedition was led by Pierre Louis Maupertuis and carried out its measurements in 1736–1737 in a part of Lapland that belonged at the time to the Kingdom of Sweden. Meanwhile, the mission to the equator, which had been organized first, proved much more challenging and took almost ten years to complete. Its members had to contend with the harsh climate and topography of the region, the prevalence of tropical diseases, and the suspicions of the local population and authorities.
The geodesic work around the equator finally began in September 1736 with the measurement of the distance between two base points chosen to lie on the plain of Yaruquí, outside the city of Quito. Those points then served as baseline for the triangulation with which the members of the mission measured an arc of about three degrees of latitude that extended to the south, past Riobamba and up to an endpoint near the city of Cuenca.
In 1737, a personal dispute between Ulloa and the new president of the Audiencia de Quito, Joseph de Araujo y Río, caused Araujo to order the arrest of both Ulloa and Juan, while announcing his intention to have them killed. The young officers took refuge in a church and Ulloa then escaped through the cordon of Araujo's men, reaching Lima and obtaining the protection of the Viceroy. In 1739 surgeon Jean Seniergues, one of the French members of the mission, was killed by a mob in the bullring in Cuenca.
After the War of Jenkins' Ear broke out between Spain and Great Britain in 1739, Juan and Ulloa were called upon to help organize the defense of the Peruvian coast. Commodore Anson had set out in from England in September of 1740 with orders to sail around Cape Horn and then attack Spanish ships and settlements along the Pacific coast. Anson successfully circumnavigated the globe in 1740–1744, but in Peru his only significant action was the attack against the town of Paita, which was plundered and burned in November 1741. Their military responsibilities due to the war with Britain kept Juan and Ulloa from scientific work for long periods and further delayed the completion of the geodesic measurements.