Jorge Juan Y Santacilia, known as Don Jorge Juan, a Spanish explorer, born at Ori-huela, Valencia, in 1712, died in Cadiz, June 21, 1774. He crossed the Atlantic in 1733 as commander of a frail polacca, explored a great portion of the American coast, and made astronomical observations which on his return to Madrid led to his election to the academy. Philip V. appointed him vice admiral, and adjoined him in 1735 to Ulloa's expedition to South America for the measurement of a degree of the meridian at the equator, with the assistance of La Condamine and Bouguer of the French academy. In 1753 he became commander of the marine guards and inspector of harbors, and promoted the efficiency of the Spanish navy. He wrote the scientific part of Ulloa's Relacion of the expedition to South America and of the measurement at the equator (see Ulloa, Antonio de), and jointly with him published a historical and geographical dissertation on the Spanish-Portuguese meridian boundary line (Madrid, 1749; French, Paris, 1776). His other works include a manual of navigation (Madrid, 1757), and a work relating to the application of technology to ship building (2 vols., Madrid, 1761-77), which has been translated into English and French.