In fact, compass, astrolabe, timepiece, and charts, were all in use on the Mediterranean about 1400, just as they were to be found among the Arab traders of the Indian Ocean.
In this section it will be enough to glance hastily at the later and growingly independent science of Christendom, from the time that it ceased merely to follow the lead of Islam, and thought and even invented for itself. In another chapter we have seen something of the lasting and penetrating influence of Greek and Moslem and Hindu tradition upon the Western thought, which has conquered by absorbing all its rivals; we must not forget that some original self-reliant work in geographical theory not less than in practical exploration is absolutely needed to explain the very fact of Prince Henry and his life—a student's life, far more even than a statesman's. And after all, the invention of instruments, the drawing of maps and globes, the reckoning of distances, is not less practical than the most daring and successful travel. For navigation, the first and prime demand is a means of safety, some power of knowing where you stand and where to go, such as was given to sailors by the use of the magnet.
"Prima dedit nautis usum magnetis Amalphis," says Beccadelli of Palermo, but the earliest mention of the "Black ugly stone" in the West is traced to an Englishman. Alexander Neckam, a monk of St. Albans, writing about 1180 on "The Natures Of Things," tells us of it as commonly used by sailors, not merely as the secret of the learned. "When they cannot see the sun clearly in cloudy weather, or at night, and cannot tell which way their prow is tending, they put a Needle above a Magnet which revolves till its point looks North and then stops." So the satirist, Guyot de Provins, in his Bible of about 1210, wishes the Pope were as safe a point to steer by in Faith as the North Star in sailing, "which mariners can keep ahead of them, without sight of it, only by the pointing of a needle floating on a straw in water, once touched by the Magnet."
It might be supposed from this not merely that the magnet was in use at the end of the twelfth century, but that it had been known to a few savants much earlier; yet when Dante's tutor, Brunetto Latini, visits Roger Bacon at Oxford about 1258, and is shown the black stone, he speaks of it as new and wonderful, but certain, if used, to awake suspicion of magic. "It has the power of drawing iron to it, and if a needle be rubbed upon it and fastened to a straw so as to swim upon water, the needle will instantly turn towards the Pole-Star. But no master mariner could use this, nor would the sailors venture themselves to sea under his command if he took an instrument so like one of infernal make."
SKETCH-MAP OF DULCERT'S PORTOLANO OF 1339.
[(see list of maps)]
It was possibly after this that the share of Amalphi came in; it may have been Flavio Gioja, or some other citizen of that earliest commercial republic of the Middle Ages, which filled up so large a part of the gap between two great ages of progress, who fitted the magnet into a box, and by connecting it with the compass-card, made it generally and easily available. This it certainly was before Prince Henry's earliest voyages, where he takes its use for granted even by merchant coasters, "who, beyond hugging the shore, know nothing of chart or needle." In any case it would seem that prejudice was broken down, and the mariner's compass taken into favour, at least by Italian seamen and their Spanish apprentices, in the early years of the fourteenth century, or the last years of the thirteenth, and that when the Dorias set out for India by the ocean way in 1291, and the Lisbon fleet sailed for the western islands in 1341, they had some sort of natural guide with them, besides the stories of travellers and their own imaginings. About the same time (c. 1350) mathematics and astronomy began to be studied in Portugal, and two of Henry's brothers, King Edward and the Great Regent Pedro, left a name for observations and scientific research. Thus Pedro, in his travels through most of Christendom, collected invaluable materials for discovery, especially an original of Marco Polo and a map given him at Venice, "which had all the parts of the earth described, whereby Prince Henry was much furthered."
Good maps indeed were almost as valuable to him as good instruments, and they are far clearer landmarks of geographical knowledge. There are at least seven famous charts (either left to us or described for us) of the fourteenth and early fifteenth centuries, which give a pretty clear idea of what Henry's own age and his father's thought and knew of the world—some of which we believe to have been used by the Prince himself, and each of which follows some advance in actual exploration.
First of all comes the Venetian map of Marino Sanuto, drawn about 1306, and putting into map-form the ideas that inspired the first Italian voyages in the Atlantic. On this the south of Africa is washed by the sea as the Vivaldi had hoped to find it, but the old story of a central zone "uninhabitable from the heat" still finds a place, helping to keep up the notion of the Tropical Seas, "always kept boiling by the sun," that held its own so long. Besides this, in Sanuto's map there is no evidence that anyone had really been coasting Africa; Henry is not anticipated and can hardly have been much helped by this very hypothetical leap in the dark.