Pliny, the celebrated encyclopedist of ancient times, says that “while the power of Carthage was at its height, Hanno published an account of a voyage which he made from Gades [Cadiz, Spain], to the extremity of Arabia.[82] ... Besides, we learn from Cornelius Nepos, that one Eudoxus, a contemporary of his, when he was fleeing from King Lathyrus, set out from the Arabian Gulf, and was carried as far as Gades.[83] And long before him, Cælius Antipater informs us that he had seen a person who had sailed from Spain to Æthiopia for the purpose of trade. The same Cornelius Nepos, when speaking of the northern circumnavigation, tells us that Q. Metellus Celer, the colleague of L. Afranius in the consulship, but then a proconsul in Gaul,[84] had a present made to him by the king of the Suevi,[85] of certain Indians, who, sailing from India for the purpose of commerce, had been driven by tempests to Germany.”[86]
These statements were quoted in the fourteenth and fifteenth centuries to support the growing belief that India could be reached in a short time by sailing round the coast of Africa. But the want of nautical instruments restrained seamen from undertaking a voyage which carried them beyond the sight of familiar coasts and beneath new constellations. It was extremely perilous for European navigators to attempt to sail to India before they had acquired a knowledge of the use of the mariner’s compass and of the astrolabe. The polarity of the magnet was known among oriental nations several centuries before the Christian era. The use of the magnetic needle for the guidance of vessels, however, did not become popular in Europe until as late as the fourteenth century.[87] The slowness with which its use grew into favor with European seamen is ascribable to the prevailing superstition which hung like a darkening cloud over the minds of the people. The strange conservatism of the age is well described in a letter written, as it seems, in the year 1258, by Brunetto Latini, a learned Italian, Dante’s tutor, to Guido Cavalcanti of Florence. Speaking of his visit to Roger Bacon, the English philosopher and monk, at Oxford, England, he says:
“The Parliament being summoned to assemble at Oxford, I did not fail to see Friar Bacon as soon as I arrived, and [among other things] he showed me a black ugly stone, called a magnet, which has the surprising property of drawing iron to it; and upon which, if a needle be rubbed, and afterwards fastened to a straw, so that it shall swim upon water, the needle will instantly turn toward the pole-star; therefore, be the night ever so dark, so that neither moon nor star be visible, yet shall the mariner be able, by the help of the needle, to steer his vessel aright.[88]
“This discovery, which appears useful in so great a degree to all who travel by sea, must remain concealed until other times, because no master-mariner dares to use it lest he should fall under a supposition of his being a magician; nor would even the sailors venture themselves out to sea under his command if he took with him an instrument which carries so great an appearance of being constructed under the influence of some infernal spirit. A time may come when these prejudices, which are of such great hindrance to researches into the secrets of nature, will probably be no more; and then it will be that mankind shall reap the benefit of the labors of such learned men as Friar Bacon, and do justice to that industry and intelligence for which he and they now meet with no other return than obloquy and reproach.”[89]
About the beginning of the fourteenth century, Flavia Gioja of Amalfi, in Naples, devised what were then known as the eight points of the superficies—the four cardinal and the four intermediate points of the compass-card.[90] From this time forward the use of the magnet gradually found favor with European seamen.
The most enthusiastic projector of voyages of discovery undertaken to ascertain the character of the land and water divisions of the earth, in the early part of the fifteenth century, was Prince Henry, the son of King John I. of Portugal.[91] When twenty-one years of age, he witnessed, in 1415, the taking of Ceuta, on the northern coast of Africa, opposite the southern extremity of Portugal. While at this opulent city, he learned from its merchants and traders that the continent extended far southward and was inhabited by many strange people. Fixing his residence on the promontory of Sagres, at the southwestern extremity of Portugal, he began to send the most experienced seamen in the service of Portugal to explore the western coast of Africa. For a time Cape de Não, in north latitude, 28° 45´ was considered the limit of safe navigation. It was a common saying among Portuguese seamen, that “He who should pass Cabo de Não, either will return or not.”[92] Beyond it was Cape Bojador, in 26° 12´ north latitude. This rocky headland, for a time, was also deemed perilous and impassable. “Beyond this cape” it was said, “there is no people whatever; the ground is as barren as that of Libya,—no water, no trees, no grass in it; the sea is so shallow that at a league from the land it is only a fathom deep; the currents are so strong that a ship passing the cape cannot return.”[93] The attempts made by Prince Henry’s mariners to double the two capes are thus commented upon by Antonio Galvano, the Portuguese historian,[94] in his treatise respecting the routes by which spices came from India to the year 1550: “In those days none of the Portuguese had yet passed Cabo de Não in 29 degrees of latitude.” But after it was doubled, “when they came to another cape named Bojador, there was not one of them that dared to risk his life beyond it. The prince was exceedingly displeased with their want of confidence and unmanly timidity.”[95] Of the number of seamen that had made unsuccessful attempts to pass the cape was Gil Eannes. Disappointed as Prince Henry was by these failures to accomplish that which he had ordered them to do, he nevertheless gave his timorous navigators all the encouragement he could to induce them to make other and more persistent efforts to double the formidable headland. In 1434, he again sent Gil Eannes to explore the coast beyond Cape Bojador. Before the latter departed the prince endeavored to dispel the terrifying fancies that might deter him from attempting to prosecute the undertaking for which he was commissioned. “You cannot incur such peril” said the prince, “that the promised reward shall not be commensurate thereto. It is very strange to me that you should be governed by a fear of something of which you are ignorant, for if the things reported had any authentication, I should not find fault with you for believing them. The stories of the four seamen driven out of their course to Flanders or to the ports to which they were sailing are not to be credited, for they had not and could not have used the needle and the chart. But do you go notwithstanding, and make your voyage without being influenced by their opinions, and, by the grace of God, you will not fail to secure, by your enterprise, both honor and compensation.”[96] Gil Eannes followed the advice of his sanguine patron, and succeeded the same year in doubling Cape Bojador and in exploring a part of the coast beyond it.
South of Cape Bojador it was believed that a zone of scorching heat would be entered by vessels sailing toward the equator. Pliny adverts to it in these words: “The middle of the earth, over which is the path of the sun, is parched and set on fire by the luminary, and is consumed by being so near the heat. There are only two of the zones which are temperate—those which lie between the torrid and the frigid zones—and these are separated from each other, in consequence of the scorching heat of the heavenly bodies.”[97] Conceiving this statement to be as fallacious as many other declarations of the early geographers had been, Prince Henry, in 1454, sent Luigi da Cadamosto, a Venetian navigator, to explore the coast beyond Cape Bojador so long invested with so many imaginary terrors. In 1462 Pedro de Cintra sailed three hundred miles beyond Sierre Leone.
As it was necessary for seamen to know the latitude and longitude of the places to which they desired to sail, another nautical instrument besides the mariner’s compass was needed by them.[98] The adaptation of an instrument called the astrolabe, by which the latitudes of places could be determined, apparently originated with King John II. of Portugal.[99]
It is said that “when Prince Henry began the discovery of Guinea that all mariners were accustomed to sail along the coasts, and that they always steered their courses by observing the physical features of the land, which are still used as guides.”
“This method of navigating permitted them to make voyages from place to place; but when they wished to sail in the open sea, losing sight of the coast and standing out on the wide ocean, they perceived the numerous errors they had made in calculating and judging the day’s run, for they had been accustomed to allow so much way to the ship in the twenty-four hours on account of the currents and the other mysteries of the sea, the facts of which are clearly demonstrated by navigating by altitude. But as necessity is the teacher of all arts, in the time of King John II., the matter of navigation was assigned by him to Master Roderic, and Master Joseph, a Jew, (who were his physicians,) and to one Martin of Bohemia, a native of those parts, who boasted of being a pupil of John of Monteregius, a famous astronomer among the professors of that science,[100] and these devised the way of navigating by the sun’s altitude, and they made tables of his declination such as are now used by navigators, now more complete than they were at the beginning when the great wooden astrolabes were first used.”[101]