In 1418, therefore, he turned his back on personal ambition, laid aside the glory of military renown, and sat himself down to a hermit's life and a scholar's labors on the promontory of Sagres, in the province of Algarve, that point on the coast of Portugal which stretches farthest out into the Atlantic in the direction of his hope. Here he built an observatory whose light was the last his captains saw as they went forth, and the first to greet them on their return. Here he opened a school of navigation, and here were trained the discoverers who opened the way for all who came afterward. Here was not only nourished the impulse which fired the hearts of Columbus and his contemporaries, but here was taught the science and here were gathered the facts which enabled them to achieve success. Up to that time, Cape Nun had been the boundary of the modern world to the southward. With infinite patience, Prince Henry labored to convince his captains that the terrors which they thought lay at the southward of this point were wholly imaginary. Little by little his caravels crept down the coast of Africa. Every year he sent out two or three. Navigators and geographers flocked to his service. In two years he re-discovered Madeira and Porto Santo, of which latter he afterward made Perestrello, the father of Columbus's wife, the governor. By 1433 his ships had reached Cape Bojador; eight years afterward they passed Cape Blanco; in 1445 they were at the mouth of the Senegal. Still he urged them on toward that "_thesaurus Arabum et divitia Indiae_," to which he set himself the task of opening up the way. The crown of Portugal assumed all the cost of these expeditions. Gold, ivory, cinnabar, dye-woods, spices, and slaves, added to the wealth of the kingdom only to furnish forth new ventures. He died before the end came, but not until many of the most important problems of cosmographic condition had been solved. It was known by actual experience that the "steaming sea" was a myth. Ships had crossed the equator, and their crews came back to tell of southward-stretching shadows. Ships were able, it was seen, to sail up the southern slope of the world as well as down it. Why they did not fall off into space, none knew, but that they did not was proved. Gravitation was a force whose laws and character were yet unformulated. The diurnal motion of the earth was hardly suspected until a hundred years later. But the facts on which these two fundamental truths are based were being gathered for Newton and Copernicus. When he died, those whom he had inspired and instructed continued the work to which he had devoted himself, under the patronage of his brother Alfonso and his nephew Joao II.; until, in 1486, Bartholomeo Diaz had sailed two hundred miles to the eastward of the Cape of Good Hope and returned to assure his sovereign that the way to India had at length been found.