Thus, at the very beginning of the fifteenth century European explorers had the benefit of the traditional ancient geography, of the new exactness of knowledge drawn from the observations of recent travellers, of the accurate but limited portolani of the Italian navigators, and finally of the more pretentious, if vague and often misleading, world maps of learned geographers. If a sailor wished to navigate the Mediterranean and its adjacent waters, if he planned to sail up the coast of Europe to the British Isles and on into the Baltic, or to pass down the Atlantic coast of Africa to Cape Nun, he might rely on the maps and charts which the Italian geographers could furnish him. Or if he launched his galleys on the Red Sea he might use their guidance down the east coast of Africa to the equator. He would also find tolerably accurate descriptions of all the southern coasts of Asia. In the interior a traveller by land could know beforehand the main features of the countries he might traverse. Beyond these limits, either by sea or by land, geographical knowledge must be sought by discovery or followed along the lines of dim report. If European sailors should follow the coast of Africa below the twenty-seventh parallel of north latitude, or of Europe above the sixtieth, or if they should direct their course into the western ocean beyond the Azores, they would be sailing into the unknown, and whatever they should find would be fresh acquisition.
The two instruments which were the most requisite for distant voyaging, the compass and the astrolabe (the predecessor of the quadrant), were already, in 1400, known and used by Mediterranean navigators. The property of turning towards the north, possessed by a magnetized needle, was certainly known as early as the close of the twelfth century; and even its use by sailors to find their directions when the sun and stars were obscured. More than one mediaeval writer describes the process by which a needle is rubbed on a piece of magnetic iron, then laid on a straw or attached to a piece of cork, and floated on water till its point turns towards the north star. [Footnote: Alexander Neckham, De Utensilibus; De Natura Rerum, book II., chap, xcviii.; Guyot de Provins, La Bible, Jacques de Vitry, Historia Orientalis; Brunette Latini, Epistolas, who mentions Roger Bacon as showing him a magnet at Oxford in 1258. Quoted in Beazley, Hakluyt Soc, Publications, 1899, cxliv., etc.] But its properties savored of magic; the earlier sailors, who hugged the shore, scarcely needed it, and it came into general use as slowly and imperceptibly as most of the other great inventions of the world.
The introduction of the compass into general use is, by tradition, ascribed to the Italian city of Amain, and it is easy to believe that the enterprising sailors of this commercial republic brought it into established recognition. By the early years of the fifteenth century the compass was provided with the card, marked with the directions, placed in the compass-box, and made a well-known part of the equipment of the navigator. [Footnote: Azurara, Discovery of Guinea, chap ix.] The mariner could now tell his directions wherever he might be, and the spider-web net-work of "compass-roses" on many of the early maps shows how anxious the map-maker was to provide lines along which the navigator might lay his course according to his compass. The makers of the better class of portolani evidently had the use of the compass in drawing their charts. [Footnote: Santarem, Essai sur L'Histoire de la Cosmographie, I., 280-305.] The changed position of the heavenly bodies as the early traveller passed northward or southward struck him with especial force. Marco Polo, describing the island of Sumatra, says, "But let me tell you one marvellous thing, and that is the fact that this island lies so far to the south that the north star, little or much, is never to be seen." [Footnote: Marco Polo (Yule's ed.), book III., chap. ix.] He also notes on his journey northward through India, when he sees it again, "two cubits above the water." When Cadamosto, the Venetian, saw the pole-star at "the third of a lance's length above the edge of the waves," he recorded it as one of the most striking phenomena of his journey towards the equator.
Two instruments were known by which the elevation above the horizon of the pole-star, or any other heavenly body could be measured. The older of these was the "cross-staff," or St. James's staff, a simple rod marked into degrees, at the end of which the eye was placed and along which a measured cross-piece was pushed, till one of its ends hid a point oh the horizon and the other the sun or star whose height was being measured. The astrolabe was a somewhat more elaborate instrument, consisting of a brass circle marked with degrees, against which two movable bars were fastened, each provided at the ends with a sight or projecting piece pierced by a hole. This was hung by a ring from a peg in the mast or from the hand, so that gravity would make one of its bars horizontal. Then the other bar was sighted to point towards some heavenly body. Chaucer, in 1400, gave to his "litel Lowis my sone" an astrolabe calculated "after the latitude of Oxenford," and wrote a charming treatise to explain to him in English its use, "for Latin ne canstow yit but smal, my lyte sone." In this treatise he described to him, among other things, "diverse tables of longitudes and latitudes of sterres." [Footnote: Chaucer, A Treatise on the Astrolabe, Prologue; Skeat, The Student's Chaucer, 396.] By means of either of these instruments latitude could be measured or calculated. Longitude was a more difficult problem; it involved the calculation of the difference of time as well as measurements of elevation of the heavenly bodies. The calculations necessary to discover actual locations from an observation were too long and complicated to be made on each occasion; and "ephemerides," or calculated tables of elevations of planets and of differences of time, were required. Just when the earliest of such tables were constructed and when chronometers came into use is obscure, but they were in existence in at least a rudimentary form early in the fifteenth century. [Footnote: Humboldt, Examen Critique, I., 274.]
The condition of Europe early in the fifteenth century as compared with its condition early in the thirteenth shows a great advance in those lines which made extensive exploration possible, and this advance was chiefly due to Italians. Increased knowledge, improved equipment, instruments of astronomical observation, navigating charts, and a face of educated navigators, made a part of the European background of American history as truly as did the incentive to exploration afforded by the search for new routes to the East. Of course much progress remained to be accomplished in the making of maps and globes, in the improvement of instruments, and in the calculation of tables during the period of discovery. The awakened scientific interest which had already shown itself as part of the Renaissance found scope in the practical requirements of distant voyages. While men were discovering new continents and seas, they were at the same time solving many problems of geographical science and perfecting the equipment by which further advance was made practicable.
CHAPTER IV
PIONEER WORK OF PORTUGAL (1400-1527)
The great period of explorations, of which the discovery of America was a part, lay between the years 1485 and 1520, between the discovery of the Cape of Good Hope by Diaz and the circumnavigation of the globe by the ships of Magellan. Long before this period of fruition, however, there was a significant movement of discovery, and an important acquisition of knowledge, experience, and boldness in exploration. This early dawn, preparatory to the later day, consisted in a series of discoveries on the west coast of Africa, due to the energy of the Portuguese and to the enlightenment of their great Prince Henry.
Portugal was especially fitted to be the pioneer in modern maritime exploration. Without geographical or racial separation from the rest of the Iberian peninsula, the national distinctness of Portugal was largely a matter of sentiment gathering around the sovereign. The nationality of Portugal had been created in the first place by the policy of its rulers, and preserved by them until the growth of separate material interests, a national language and literature, and traditions of glorious achievements confirmed the separateness of the Portuguese nationality from that of Spain.
The desire to hold aloof from other Spanish countries turned the attention of the king of Portugal to more distant alliances, and the open western seaboard naturally suggested that these should be with maritime states. In 1294 a treaty of commerce was signed with England. A century later, 1386, a much closer alliance with that country was formed and a new treaty signed at Windsor. [Footnote: Rymer, Foedera, II., 667, VII., 515-523.] This was followed in the next year by a marriage between the king of Portugal and Philippa, daughter of the English John of Gaunt and first cousin of King Richard. This "Treaty of Windsor" was renewed again and again by succeeding English and Portuguese sovereigns and remained the foundation of their relationship until it was superseded long afterwards by still closer treaty arrangements. With Flanders, Portugal had frequent peaceful intercourse, both in trade and in diplomacy. A Venetian fleet also called from time to time at the harbor of Lisbon on the way to and from England and Flanders, and thus brought Portugal into contact with the great Italian republic, and may have aroused an interest in far Eastern trade products of which loaded the galleys.