At first, though, if the plan of sailing west was even thought of, it would seem to have been regarded as less feasible than that of rounding Africa. Prince Henry, a son of King John I of Portugal—for it was the Portuguese, not the Spanish, who were the pioneers in this series of discoveries—determined to devote his life to the work. Retiring from the splendors of the Lisbon court, he built an astronomical observatory on the promontory of Sagres (in southern Portugal), extended its hospitalities to all the wise men of the age and sent out expedition after expedition to the south. “Until then,” says Dawson, “nautical knowledge was very meager. The compass served only to indicate direction, not distance or position, and did not suffice for the systematic navigation of the open Atlantic. The Portuguese first made that possible by using astronomical observations and inventing the quadrant and astrolabe.” This knowledge, once acquired, was promptly applied. Madeira was discovered in 1418, the Canaries in 1427, the Azores in 1432. To the west the Portuguese ventured no farther, but, continuing south, they reached Cape Blanco in 1441, Senegambia and Cape Verde in 1445, the Cape Verde Islands in 1460, and the Gulf of Guinea in 1469. In 1471 they were the first Europeans to cross the equator. The idea was then conceived that they had only to keep on and they could round the southern extremity of the continent and reach Abyssinia and India by sea—a hope that was realized in 1487 when Bartholomew Dias arrived at last at the Cape of Good Hope. A few miles beyond, however, he was compelled by the condition of his crew to return and it remained for his compatriot Vasco da Gama some years later to double the cape and complete the voyage up the eastern coast and across the Indian Ocean to Hindustan. II The significance of these early voyages of the Portuguese lies in the fact that thereby it was demonstrated that a shorter route was needed—that with the very small and badly equipped vessels of the period the trip around the Cape of Good Hope, at least for commercial purposes, was impracticable; also in the fact that with Dias had sailed the Genoese navigator Bartholomew Columbus, a brother of the discoverer of America.