At this time nearly all the commerce of Europe, mainly in Italian hands, was with India and China. The overland route was long, perilous, and expensive, and that across the Arabian Gulf hardly less so. At best, such traffic was slow and limited, and the first need of the reviving world was the discovery of some straighter and quicker road to the East. In this quest Portugal came forward under the brilliant leadership of Dom Henrique (Prince Henry), styled “the Navigator,” who was the younger son of King João (or John) I, and half an Englishman, since his mother was Philippa of Lancaster. It was Prince Henry’s ambition to extend geographical discovery and improve seamanship, and he enlisted the help of the best navigators obtainable, regardless of nationality. In order to observe the heavens to better advantage, and also to study the tides and other nautical phenomena, he established an observatory on the bleak headland of Cape Sagres, where he willingly spent a large portion of his time for the sake of science. Navigation was sorely in need of such help. Except that they had rude compasses, of whose laws of variation, etc., they were ignorant, the seamen of that day were little, if any, better equipped than were those who sailed the “ships of Tarshish” a thousand years before that. Astronomers had supplied them with rough tables of the declination of the sun, pole-star, etc., by which, with the help of a cross-staff,—a simple instrument for ascertaining angles,—they might make a guess at the latitude. Longitude was found only by observations of eclipses of the moon, and noting the difference between the time when it was due at home, according to the almanac, and the local time of its actual coming; but at sea the “observations” were little better than guessing. Chart-making was an important branch of study at Sagres. So few and rare were sea-maps then that one was never seen in England until 1489. To the collection of information in this direction, and the improvement of nautical methods, Prince Henry and his aids applied themselves most diligently; but he died before much had been accomplished. Nautical studies went on, however, under the next king, John II, for whom Martin of Bohemia, the foremost astronomer of his time, devised a form of the astrolabe for use on shipboard, increasing accuracy in finding latitude. It was with no better instruments than these (and sand-glasses in place of chronometers) as guides over chartless and unsounded seas that the way was found to India and to America, and the globe was circumnavigated; and that the same thing might be done again is shown by the fact that only last year (1897) a vessel, which had barely escaped destruction in a storm and lost all her instruments in the mid-Pacific, was brought safely into San Francisco by observation of the stars and “dead-reckoning” alone.