A principal factor in the development of map-making, as of navigation, had been the magnet. It had been brought from China to the eastern coast of Africa as early as the fourth century, and through the Arabs[368] and Crusaders it had been introduced into the Mediterranean, and was used by the Catalans and Basques in the twelfth century, a hundred years or more before Marco Polo brought to Europe his wonderful stories.[369] In that century even it had become so familiar a sight that poets used it in their metaphors. The variation of its needle was not indeed unknown long before Columbus, but its observation in mid-ocean in his day gave it a new significance. The Chinese had studied the phenomenon, and their observations upon it had followed shortly upon the introduction of the compass itself to Western knowledge; and as early as 1436 the variation of the needle was indicated on maps in connection with places of observation.[370] The earliest placing of a magnetic pole seems due to the voyage of Nicholas of Lynn, whose narrative was presented to Edward III. of England. This account is no longer known,[371] though the title of it, _Inventio fortunata_, is preserved, with its alleged date of 1355. Cnoyen, whose treatise is not extant, is thought to have got his views about the regions of the north and about the magnetic pole from Nicholas of Lynn,[372] while he was in Norway in 1364; and it is from Cnoyen that Mercator says he got his notion of the four circumpolar islands which so long figured in maps of the Mercator and Finæus school. In the Ruysch map (1508) we have the same four polar islands, with the magnetic pole placed within an insular mountain north of Greenland. Ruysch also depended on the _Inventio fortunata_. Later, by Martin Cortes in 1545, and by Sanuto in 1588, the pole was placed farther south.[373] Ptolemy, in the second century, accepting the generally received opinion that the world as known was much longer east and west than north and south, adopted with this theory the terms which naturally grew out of this belief, _latitude_ and _longitude_, and first instituted them, it is thought, in systematic geography.[374] Pierre d’Ailly, in his map of 1410,[375] in marking his climatic lines, had indicated the beginnings, under a revival of geographical inquiry, of a systematic notation of latitude. Several of the early Ptolemies[376] had followed, by scaling in one way and another the distance from the equator; while in the editions of 1508 and 1511 an example had been set of marking longitude. The old Arabian cartographers had used both latitude and longitude; but though there were some earlier indications of the adoption of such lines among the European map-makers, it is generally accorded that the scales of such measurements, as we understand them, came in, for both latitude and longitude, with the map which Reisch in 1503 annexed to his _Margarita philosophica_.[377]