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.