We Allude, Principally, To The Discovery Of The Mariners' Compass.

The first clear notice of it appears in a Provencal poet of the end of the twelfth century.

In the thirteenth century it was used by the Norwegians in their voyages to and from Iceland, who made it the device of an order of knighthood of the highest rank; and from a passage in Barber's Bruce, it must have been known in Scotland, if not used there in 1375, the period when he wrote. It is said to have been used in the Mediterranean voyages at the end of the thirteenth or beginning of the fourteenth century.

With respect to the nations of the east, it is doubted whether they derived their knowledge of it from the Europeans, or the Europeans from them. When we reflect on the long and perilous voyages of the Arabians, early in the Christian era, we might be led to think that they could not be performed without the assistance of the compass; but no mention of it, or allusion to it, occurs in the account of any of their voyages; and we are expressly informed by Nicolo di Conti, who sailed on board a native vessel in the Indian seas, about the year 1420, that the Arabians had no compass, but sailed by the stars of the southern pole; and that they knew how to measure their elevation, as well as to keep their reckoning, by day and night, with their distance from place to place. With respect to the Chinese, the point in dispute is not so easily determined: it is generally imagined, that they derived their knowledge of the compass from Europeans: but Lord Macartney, certainly a competent judge, has assigned his reasons for believing that the Chinese compass is original, and not borrowed, in a dissertation annexed to Dr. Vincent's Periplus of the Erythrean Sea. At what period it was first known among them, cannot be ascertained; they pretend that it was known before the age of Confucius. That it was not brought from China to Europe by Marco Polo, as some writers assert, is evident from the circumstance that this traveller never mentions or alludes to it. The first scientific account of the properties of the magnet, as applicable to the mariner's compass, appears in a letter written by Peter Adsiger, in the year 1269. This letter is preserved among the manuscripts of the university of Leyden; extracts from it are given by Cavallo, in the second edition of his Treatise on Magnetism. From these extracts it is evident that he was acquainted with the attraction, repulsion, and polarity of the magnet, the art of communicating those properties to iron, the variation of the magnetic needle; and there are even some indications that he was acquainted with the construction of the azimuth compass.

Next in importance and utility to the mariners' compass, in preparing the way for the great discoveries by which the fifteenth century is distinguished, maps and charts may be placed. For though, in general, they were constructed on very imperfect and erroneous notions of the form of the world, and the relative size and situation of different countries, yet occasionally there appeared maps which corrected some long established error, or supplied some new information; and even the errors of the maps, in some cases, not improbably held out inducements or hopes, which would not otherwise have been entertained and realized, as we have already remarked, after D'Anville, that the greatest of Ptolemy's errors proved eventually the efficient cause which led to the greatest discovery of the moderns.

Malte Brun divides the maps of the middle ages into two classes: those in which the notions of Ptolemy and other ancient geographers are implicitly copied, and those in which new countries are inserted, which had been either discovered, or were supposed to exist.

In most of the maps of the first description, Europe, Asia, and Africa are laid down as forming one immense island, and Africa is not carried so far as the equator. One of the most celebrated of these maps was drawn up by Marin Sanuto, and inserted in his memorial presented to the pope and the principal sovereigns of Europe, for the purpose of persuading and shewing them, that if they would oblige their merchants to trade only through the dominions of the Caliphs of Bagdat, they would be better supplied and at a cheaper rate, and would have no longer to fear the Soldans of Egypt. This memorial with its maps was inserted in the Gesta Dei per Francos, as we are assured by the editor, from one of the original copies presented by Sanuto to some one of the princes. Hence, as Dr. Vincent remarks, it probably contains the oldest map of the world at this day extant, except the Peutingerian tables. Sanuto, as we have already noticed, in giving an abstract of the commercial information contained in his memorial, lived in 1324.

In the monastery of St. Michael di Murano, there is a planisphere, said to be drawn up in 1459, by Fra Mauro, which contains a report of a ship from India having passed the extreme point south, 2000 miles towards the west and southwest in 1420.

Ramusio describes a map, supposed to be this, which he states to have been drawn up for the elucidation of Marco Polo's travels.

On this map, so far as it relates to the circumnavigation of Africa, Dr. Vincent has given a dissertation, having procured a _fac-simile_ copy from Venice, which is deposited in the British Museum; the substance of this dissertation we shall here compress. He divides his dissertation into three parts. First, whether this was the map noticed by Ramusio, and by him supposed to be drawn up to elucidate the travels of Marco Polo. On this point he concludes that it was the map referred to by Ramusio, but that his information respecting it is not correct. The second point to be determined is, whether the map procured from Venice was really executed by Mauro, and whether it existed previous to the Portuguese discoveries on the west coast of Africa.

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