Henry, Duke of Viseu, Grand Master of the Order of Christ, and governor of the Algarves, was the third son of John “the Great” and Philippa of Lancaster, and after winning great credit in the capture of Ceuta, he took up his residence at Sagre, near Cape St. Vincent, in 1418, and devoted himself to the task of maritime exploration. His father and his brothers assisted him, but they recognized his special fitness for the work, and therefore, though encouraging him as much as possible, they did not interfere with his projects, and made no attempts to contest his well-earned title of Prince Henry “the Navigator.”[9] The prince was too wise to neglect scientific knowledge, and he therefore summoned learned mathematicians and astronomers from all parts of Europe to his aid. Enjoying immense wealth, he established an observatory and a school of navigation at Sagre, where he employed the men of science in making charts and, above all, in improving the working of the compass. This was the theoretical side of his work; the practical was not less important. He collected together all the most daring captains and mariners he could find, and sent them forth year by year on voyages of discovery along the western coast of Africa. He never went on any of these expeditions in person, but he was acknowledged by all the men of science and sailors in his pay to be their master and presiding genius. [Illustration: ST. SALVADOR IN THE SIXTEENTH CENTURY. (_From Braun and Hohenberg’s Civitates orbis terrarum. 1574._)]