In order to promote his designs, Prince Henry was appointed Commander-in-chief of the Portuguese forces in Africa. He had already, in 1412, three years before the reduction of Ceuta,[44] sent a ship to make discoveries on the Barbary coast. Cape Nam[45] (as its name implies) was then the _ne plus ultra_ of European navigation; the ship sent by Henry, however, passed it sixty leagues, and reached Cape Bojador. About a league and a half from Cape St. Vincent (supposed to be the Promontorium Sacrum of the Romans), Prince Henry built his town of Sagrez, the best planned and fortified town in Portugal. Here, where the view of the ocean inspired his hopes, he erected his arsenals, and built and harboured his ships. And here, leaving the temporary bustle and cares of the State to his father and brothers, he retired like a philosopher from the world in order to promote its happiness. Having received all the information he could obtain in Africa, he continued unwearied in his mathematical and geographical studies; the art of ship-building received amazing improvement under his direction, and the correctness of his ideas of the structure of the globe is now confirmed. He it was who first suggested the use of the mariner's compass, and of longitude and latitude in navigation, and demonstrated how these might be ascertained by astronomical observations. Naval adventurers were now invited from all parts to the town of Sagrez, and in 1418 Juan Gonsalez Zarco and Tristran Vaz set sail on an expedition of discovery, the circumstances of which give us a striking picture of the state of navigation ere it was remodelled by the genius of Henry.
Cape Bojador, so named from its extent,[46] runs about forty leagues to the westward, and for about six leagues off land there is a most violent current, which, dashing upon the shallows, makes a tempestuous sea. This was deemed impassable, for it had not occurred to any one that by standing out to sea the current might be avoided. To pass this formidable Cape was the commission of Zarco and Vaz, who were also ordered to survey the African coast, which, according to the information given to Henry by the Moors, extended to the Equator. Zarco and Vaz, however, lost their course in a storm, and were driven to a small island, which, in the joy of their deliverance, they named Puerto Santo, or the Holy Haven. Nor was Prince Henry less joyful of their discovery than they had been of their escape: sufficient proof of the miserable state of navigation in those days; for this island is only a few days' voyage from Sagrez.