Chapter 5

The conception of the sphericity of the earth was really a matter of mental training. In the fifteenth century those who had gained this knowledge were fewer than in modern times, but the class who did so believe were no less sure of it. Astronomers, philosophers, men of general learning, and even navigators and pilots were quite familiar with the idea and quite in the habit of thinking of the earth as a sphere. In all probability Columbus represented the beliefs of his class, as well as his own, when he said, "I have always read that the world, comprising the land and the water, is spherical, as is testified by the investigations of Ptolemy and others, who have proved it by the eclipses of the moon and other observations made from east to west, as well as by the elevation of the pole from north to south." [Footnote: Hakluyt Soc., Publications, Hist. of Columbus--Third Voyage, II., 129.] Opposition to voyages westward was based rather on the probability of the enormous size of the earth and on the supposed difficulty of sailing up the slope of the sphere than it was upon any serious doubt of its sphericity.

The habitable world was quite a different conception. It consisted of Europe, Asia, and Africa, these three continents forming a continuous stretch of land lying on the surface of the spherical earth, the rest of its surface being presumably covered with water. There was more or less speculation about the existence of other habitable lands on the earth than those which were known, but the interest in this possibility was languid at best, and it was denied by learned churchmen on biblical grounds.

The map-makers of that period continued, like those of the earlier Middle Ages, to base their work on mere half-mythical traditions, unrelieved and uncorrected by the results of actual discoveries. Their maps are still much like picture-books, filled with biblical and literary lore, indicating but a slight attempt to incorporate exact measurements and outlines. A development more revolutionary than the mere gradual increase of knowledge was necessary to break the bonds of academic tradition. [Footnote: Santarem, Essai sur L'Histoire de la Cosmographie, I., 75, 167, 178.]

Just at the beginning of the fourteenth century, however, a new line was struck out in map-making by the construction and steady development of sailing charts, or "portolani." These humble attempts at geographical representation were intended as practical aids to navigation for Mediterranean mariners, and were based on practical observation. During the fourteenth and early fifteenth centuries they reached a wonderful degree of accuracy. The coasts, bays, islands, and promontories of the Mediterranean were plotted out in them and drawn with striking correctness. Some four hundred such sketch-maps remain to us, drawn by Italians from the fourteenth to the sixteenth centuries, besides nearly a hundred made in other countries. [Footnote: Beazley, in Hakluyt Soc., Publications, 1899, cxx.] They did not undertake to give the internal features of the countries whose coast-lines they depicted, and as their main purpose was to aid Mediterranean trade, they did not extend so far beyond its shore as the erudition of the age would have made possible.

The best of the world maps of the fifteenth century were based on these Italian portolani rather than on mediaeval maps, and at the same time added such enlarged information as became common in the Italy of the fifteenth century. [Footnote: Ibid., cxxi., etc.]

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.