There is no reason to believe that Henry planned or wished the development of a trade in slaves; [Footnote: The statement to the contrary in the Cambridge Modern Hist., I., 10, is not deducible from any contemporary evidence.] but labor was scarce on the great estates of southern Portugal, slaves were in demand, and very different desires from those of the prince might be gratified by capturing and bringing to the slave-market of Lagos the unfortunate natives of the newly discovered coasts. Hence one expedition after another, sent out for purposes of discovery, returned, bringing tales of failure to reach farther points on the coast, but laden with human booty to be sold. Private adventurers sought and obtained the prince's permission to send out caravels, and these also brought home cargoes of slaves. Only the most vigorous pressure, exercised on the choicest spirits among the Portuguese captains, served now to carry discoveries farther.
Nevertheless, a basis of interest in distant voyages had been found which had not existed before; and the further exploration of the African coast was certain, even in default of the personal enlightenment and enthusiasm of the Navigator. The expeditions sent by the prince and private voyages made familiar to the mariners of Portugal two thousand miles of coast instead of six hundred as of old. Guinea was eventually reached.
In 1455 the Venetian Cadamosto entered into Henry's service; and, followed closely by Diego Gomez, discovered the Cape Verd Islands and passed so far around the shoulder of northwestern Africa as not only to reach the ends of the caravan routes from Morocco, and to open up trade in gold, ivory, and the products of the Guinea coast, but to suggest that there was open sea now all the way eastward to India. The temporary disappointment of finding that this was not true was left to the successors of Prince Henry, for his death occurred in 1460. But the work was still carried on by his nephew, Alfonso V., and by the next king of Portugal, John II.
A series of bold pilots now passed beyond the whole Guinea coast, crossed the equator, and made their way down almost two thousand miles more of the African coast. The belief became assured that "ships which sailed down the coast of Guinea might be sure to reach the end of the land by persisting to the south"; and stone pillars six feet high were ordered to be erected at landing-places to indicate possession and mark the stages of the route to the Indies.
Finally, in 1486, Bartholomew Diaz, the third member of his family to take part in the discoveries of Prince Henry, with two vessels sailed the remaining distance on the coast, and passed so far to the eastward that his sailors mutinied and refused to go farther. Diaz then suddenly realized that, notwithstanding the necessity for his return, he had at last found the passage-way to India dreamed of through so many ages and sought for at such heavy cost.
A period of still greater discoveries was already at hand. "It was in Portugal," says Ferdinand Columbus, "that the admiral began to surmise that if men could sail so far south, one might also sail west and find lands in that direction." The Portuguese were so wedded to the search for the southeast route, and it was so nearly achieved at this time, that their interest was but languid in the plans for a search to the westward. Another people therefore took it up, and soon the exploration of the New World was in full tide, and the period of pioneer effort passed into the era of great accomplishment.
Meanwhile Portugal saw the fruition of Prince Henry's work in the circumnavigation of Africa. Ten years later than the exploit of Diaz, in 1496, a fleet sailed from Lisbon under Vasco da Gama which was destined to round the Cape, make its way up the east coast of Africa till familiar parts of the Indian Ocean were reached; then to sail across to India, cast anchor, and secure cargo in Calicut and many other ancient ports; and to return thence safely to its port of departure. [Footnote: The First Voyage of Vasco da Gama, in Hakluyt Soc., Publications, 1898.] The Portuguese search for a new route to the lands of Eastern products was thus successful; and once found, this path became familiar. The fleet of Cabral in 1500 immediately followed that of Da Gama, and, driven to the westward as it sailed to the south, discovered Brazil, as a casual incident of its successful voyage to India. Thus, if the voyage of Columbus had never been undertaken, America would have been found within less than a decade.
Albuquerque followed around the southeast passage in 1503; a permanent traffic between Portugal and India was established, and thereafter yearly fleets of merchant and war vessels rounded the Cape. Soon most of the points of vantage of the Indies were in Portuguese control— Ormuz, Diu, Goa, Ceylon, Malacca—and the enterprising little western state had trade settlements in Burma, China, and Japan. [Footnote: Hunter, Hist, of British India, I., 110-133.] The private path of the Portuguese ultimately became the public highway of the nations. Spain, Holland, England, and France sent fleets around the Cape of Good Hope, and made use of the route to the East which the Portuguese had discovered.
The actual progress of scientific knowledge and practical equipment for navigation made at Sagres, Lagos, Lisbon, and on the seas, during the voyages sent out by Prince Henry and his immediate successors, is unfortunately not accurately known; but some glimpses of it may be obtained. "In his wish to gain a prosperous result of his efforts," says an almost contemporary historian, "the Prince devoted great industry and thought to the matter, and at great expense procured the aid of one Master Jacome from Majorca, a man skilled in the art of navigation and in the making of maps and instruments, and who was sent for, with certain of the Arab and Jewish mathematicians, to instruct the Portuguese." [Footnote: De Barros, Decadas da Asia, quoted in Beazley, Henry the Navigator, 161.]
When trained Italian navigators applied to Henry, as was the case with the Venetian Cadamosto, they were readily taken into his service, and he sent word by them that he would heartily welcome any other such volunteers. When the prince's work fell into the hands of his nephew, King John, the latter appointed the German Behaim, of Nuremberg, who lived in Lisbon from 1480 to 1484, to be one of the four members of his "Junto de Mathematicos." It was Behaim who introduced to the Portuguese the improved ephemerides calculated by the German Regiomontanus, and printed at Nuremberg in 1474. He also improved the astrolabe and the staff, drew charts and made globes, and accompanied one of the West- African expeditions in 1489. [Footnote: Major, Prince Henry the Navigator, 326-328.] Diego Gomez, one of Henry's captains, remarks, in describing his voyage of 1460, "I had a quadrant with me and wrote on the table of it the altitude of the arctic pole, and I found it better than the chart; for though you see your course of sailing on the chart well enough, yet if once you get wrong it is hard by map alone to work back into the right course." [Footnote: Quoted, in Beazley, Henry the Navigator, 297, 298.] Azurara also contrasts the incorrect charts with which Henry's sailors were provided before their explorations with those corrected by the later observations. [Footnote: Azurara, Discovery of Guinea, chap. Lxxvi.] His navigators, therefore, used the compass, the quadrant, and carefully constructed charts; but their advances in the use of this equipment are not recorded.