The great object of Mauro, in drawing up this map, was to encourage the Portuguese in the prosecution of their voyages to the south of Africa. This is known to be the fact from other sources, and the construction of the map, as well as some of the notices and remarks, which are inserted in its margin, form additional evidence that this was the case. Two passages, as Dr. Vincent observes, will set this in the clearest light. The first is inserted at Cape Diab; "here," says the author, about the year 1420, "an Indian vessel, on her passage across the Indian ocean was caught by a storm, and carried 2000 miles beyond this Cape to the west and south-west; she was seventy days in returning to the Cape." This the author regards as a full proof that Africa was circumnavigable on the south.
In the second passage, inserted on the margin, after observing that the Portuguese had been round the continent of Africa, more than 2000 miles to the south-west beyond the Straits of Gibraltar; that they found the navigation easy and safe, and had made charts of their discoveries; he adds, that he had talked with a person worthy of credit, who assured him he had been carried by bad weather, in an Indian ship, out of the Indian Ocean, for forty days, beyond Cape Sofala and the Green Islands, towards the west and south-west, and that in the opinion of the astronomer on board, (such as all Indian ships carry,) they had been hurried away 2000 miles. He concludes by expressing his firm belief that the sea surrounding the southern and south-eastern part of the world is navigable; and that the Indian Sea is ocean, and not a lake. We may observe, by the bye, that in another passage inserted in the margin, he expressly declares that the Indian ships had no compass, but were directed by an astronomer on board, who was continually making his observations.
It is evident that the two accounts are at variance, as the first asserts that the passage was round Cape Diab, at the termination of Africa, and the second that it was round Cape Sofala, fifteen degrees to the north of the extremity of this quarter of the world: but without attempting to reconcile this contradiction, it is abundantly evident that Mauro, by noticing the Portuguese navigators, as having reached 2000 miles to the south of Gibraltar, and adding that 2000 miles more of the coast of Africa had been explored by an Indian ship, meant to encourage the further enterprises of the Portuguese, by the natural inference that a very small space of unsailed sea must lie between the two lines, which were the limits of the navigation of the Portuguese and Indian vessel. The unexplored space was indeed much greater than Mauro estimated and represented it in his map to be; but, as Dr. Vincent remarks, his error in this respect manifestly contributed to the prosecution of the Portuguese designs, as the error of the ancient geographers, in approximating China to Europe, produced the discovery of America by Columbus.
We have dwelt thus long on the map of Mauro, as being by far the most important of the maps of the second description, or those in which were inserted real or supposed discoveries. The rest of this description require little notice.
A map of the date of 1346, in Castilian, represents Cape Bojada in Africa as known, and having been doubled at that period. A manuscript, preserved at Genoa, mentions that a ship had sailed from Majorca to a river called Vedamel, or Rui Jaura (probably Rio-do-Ouro,) but her fate was not known. The Genoese historians relate that two of their countrymen in 1291, attempted to reach India by the west; the fate of this enterprize is also unknown. The Canary Islands, the first discovery of which is supposed to have taken place before the Christian era, and which were never afterwards completely lost sight of, being described by the Arabian geographers, appear in a Castilian map of 1346. Teneriffe is called in this map Inferno, in conformity with the popular notion of the ancients, that these islands were the seat of the blessed. In a map of 1384, there is an island called Isola-di-legname, or the Isle of Wood, which, from this appellation, and its situation, is supposed by some geographers to be the island of Madeira. It would seem that some notions respecting the Azores were obscurely entertained towards the end of the fourteenth century, as islands nearly in their position are laid down in the maps of 1380.
In the library of St. Marc, at Venice, there is a map drawn by Bianco, in 1436. In it the ancient world is represented as forming one great continent, divided into two unequal parts by the Mediterranean, and by the Indian Ocean, which is carried from east to west, and comprises a great number of islands. Africa stretches from west to east parallel to Europe and Asia, but it terminates to the north of the equator. The peninsula of India and the Gulf of Bengal scarcely appear. The eastern part of Asia consists of two great peninsulas, divided by an immense gulf. Then appear Cathai, Samarcand, and some other places, the names of which are unintelligible. All the kingdoms of Europe are laid down except Poland and Hungary. To the west of the Canaries, a large tract of country is laid down under the appellation of Antitia; some geographers have maintained that by this America was indicated, but there does not appear any ground for this belief.
Having offered these preliminary and preparatory observations, we shall now proceed to the discoveries of the Portuguese. From the slight sketch which has already been given of the progress of geography and commerce, between the time of Ptolemy and the fifteenth century, it appears that the Portuguese had distinguished themselves less, perhaps, than any other European nation, in these pursuits; but, long before the beginning of the fifteenth century, circumstances had occurred, connected with their history, which were preparing the way for their maritime enterprizes. So early as the year 1250, the Portuguese had succeeded in driving the Moors out of their country; and, in order to prevent them from again disturbing them, they in their turn invaded Fez and Morocco, and having conquered Ceuta in 1415, fortified it, and several harbours near it, on the shores of the Atlantic. So zealous were the Portuguese in their enterprizes against the Moors, that the ladies of Lisbon partook in the general enthusiasm, and refused to bestow their hand on any man who had not signalized his courage on the coast of Africa, The spirit of the nation was largely participated by Prince Henry, the fifth son of John I., king of Portugal, who took up his residence near Cape St. Vincent, in the year 1406. The sole passion and object of his mind was to further the advancement of his country in navigation and discovery: his regard for religion led him to endeavour to destroy or diminish the power of the Mahometans; and his patriotism to acquire for Portugal that Indian commerce, which had enriched the maritime states of Italy. He sought every means and opportunity by which he could increase or render more accurate his information respecting the western coast, and the interior of Africa: and it is probable that the relations of certain Jews and Arabs, respecting the gold mines of Guinea, weighed strongly with him in the enterprizes which he planned, encouraged, and accomplished.
It is not true, however, that he was the inventor of the astrolobe and the compass, or the first that put these instruments into the hands of navigators, though he undoubtedly was an excellent mathematician, and procured the best charts and instruments of the age: the use and application of these, he taught in the best manner to those he selected to command his ships.
With respect to the compass, we have already stated all that is certainly known respecting its earliest application to the purposes of navigation. The sea astrolobe, which is an instrument for taking the altitude of the sun, stars, &c., is described by Chaucer, in 1391, in a treatise on it, addressed to his little son, Louis; and Purchas informs us, that it was formerly applied only to astronomical purposes, but was accommodated to the use of seamen by Martin Behaim, at the command of John II., king of Portugal, about the year 1487.
About the year 1418, when Prince Henry first began his plan of discovery, Cape Nun, in latitude 28° 40', was the limit of European knowledge on the coast of Africa. With this part of the coast, the Portuguese had become acquainted in consequence of their wars with the Moors of Barbary. In 1418, two of Henry's commanders reached Cape Boyada in latitute 26° 30'; but the Cape was not actually doubled till 1434. The Canary islands were visited during the same voyage that the Cape was discovered: Madeira was likewise visited or discovered; it was first called St. Laurence, after the saint of the day on which it was seen, and afterwards Madeira, on account of its woods. In 1420, the Portuguese set fire to these woods, and afterwards planted the sugar cane, which they brought from Sicily, and the vines which they brought from Cyprus. Saw mills were likewise erected on it.