Remembering an Enlightened Scientist: Jorge Juan (1713-1773)

Portrait of the Spanish naval officer Jorge Juan y Santacilia (1713–1773), who was also a Knight of the Order of Malta. / Wikipedia

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Xavier Massó

Born on 5 January 1713 in Novelda (Alicante), Jorge Juan y Santacilia was a humanist, scientist, naval officer, shipbuilder, intelligence agent and, in all likelihood, one of the most complete exemplars of the early Enlightenment spirit to emerge in eighteenth-century Spain. He took part in the measurement of the terrestrial meridian, demonstrating that the Earth is flattened at the poles.

Orphaned of his father at the age of three, he was educated at the Jesuit college in Alicante under the supervision of his uncle, himself a member of the order. In 1727 he entered the Royal Academy of Midshipmen in Cádiz, swiftly gaining a reputation as a gifted student thanks to his extraordinary aptitude for mathematics—so much so that his fellow pupils dubbed him “Euclid”.

He played a prominent role in the Spanish–French Geodesic Mission (1735–1744), organised by France to measure the arc of the meridian in equatorial regions. The question was whether the Earth was elongated at the poles, as Cassini argued, or flattened, as followed from Newton’s law of universal gravitation and seemed to be supported by pendulum experiments, the position championed by Halley and Huygens. This required on-site measurements of the meridian arc at differing latitudes.

The Spanish contribution fell, surprisingly for a mission of such magnitude, to two extraordinarily young yet exceptionally capable scientists: Jorge Juan, aged 21, as mathematician, and Antonio Ulloa, aged 19, as naturalist. They were so young that they still lacked military rank, and were therefore promoted directly to naval lieutenant. Their operations base was Quito, in present-day Ecuador, from which they undertook a series of triangulations ranging from lowland plains to peaks of 5,000 metres. The expedition endured great hardships and repeated interruptions owing to the outbreak of war with England. Juan calculated the value of one degree of meridian at the equator as 56,767.788 toises—roughly 110.6 km. His result was the most accurate of the entire mission, and not only confirmed that the Earth is flattened at the poles but also provided the basis, fifty years later, for the adoption of the metre as the fundamental unit of the decimal metric system, defined as one ten-millionth of the Earth’s meridian quadrant.

The return to Spain was fraught with difficulty, the country being at war with England, which commanded the seas. For safety, Juan and Ulloa travelled separately. Juan reached Brest (France) on 31 October 1745, then proceeded to Paris to exchange views with French scholars. Ulloa was not so fortunate: captured by the English, he was forced to destroy all his documents and spent a period imprisoned in England.

Upon his return to Spain—now under the reign of Ferdinand VI—Juan met the Marquis of Ensenada, who immediately recognised in him the ideal figure to reform Spain’s antiquated navy. He was dispatched to London as an intelligence agent with the aim of studying British shipbuilding techniques. Passing himself off as “Mister Josues”, he proved remarkably successful: he moved with ease in the circles of Prime Minister John Russell and was even elected a Fellow of the Royal Society, as Ulloa would later be. He succeeded in gaining access to British advances and recruited experts to work in Spain applying the new techniques.

He did not merely reproduce British designs; he improved them. Eighteen months later, the British Prime Minister ordered his arrest on charges of espionage, forcing him into a hasty escape. Back in Spain, he implemented his system in the shipyards of Cádiz, Ferrol, Cartagena and Havana, introducing at the same time a method of labour division based on specialist expertise. In Ferrol he also collaborated with the Catalan naval engineer Francisco Llobet in planning the arsenal and the Magdalena district.

His improvements were of such magnitude that the English, in due course, returned the visit and appropriated the innovations Juan had incorporated into his own designs—while also ensuring that Spain would not apply them. The downfall of Ensenada—engineered by the intrigues of the British ambassador, Benjamin Keene—brought the project to an abrupt end and led to the adoption of the French model of shipbuilding, markedly inferior to Juan’s.

Jorge Juan pursued his scientific work with equal distinction. In Cádiz he founded the “Friendly Literary Assembly”, a society that met to discuss matters of shared intellectual interest and counted among its members Louis Godin, José Infante, Francisco Canivell, José Nájera, Pedro Virgili and José Carbonell. Conceived as the embryo of a future Spanish Academy of Sciences, the project ultimately failed to materialise. He also founded the Madrid Astronomical Observatory and served for a time as ambassador to Morocco. In all his endeavours he stood out for his exceptional competence and clear-sighted judgement.

Jorge Juan y Santacilia died in Madrid on 21 July 1773, aged sixty, from a bilious colic.

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