page_title: Gerardus Mercator
section_title: Duisburg 1552–1594
hierarchical_section_title: Gerardus Mercator / Mercator's life / Duisburg 1552–1594
caption_attribution_description: Latina: Tab. I. Africæ, in qua Mauritania Tingitana et Cæsariensis :medius meridianus 16, reliqui ad hunc inclinati sunt pro ratione parellelorum 29 et 34 ad circulum maximum. English: Ptolemy's First Map of Africa, with Mauretania Tingitana and Caesariensis, covering modern Morocco and western Algeria.
context_page_description: Gerardus Mercator was a 16th-century geographer, cosmographer and cartographer from the County of Flanders. He is most renowned for creating the 1569 world map based on a new projection which represented sailing courses of constant bearing as straight lines—an innovation that is still employed in nautical charts.
  Mercator was one of the pioneers of cartography and is widely considered the most notable figure of Netherlandish school of cartography in its golden age. In his own day, he was a notable as maker of globes and scientific instruments. In addition, he had interests in theology, philosophy, history, mathematics and geomagnetism. He was also an accomplished engraver and calligrapher.
  Unlike other great scholars of the age he travelled little and his knowledge of geography came from his library of over one thousand books and maps, from his visitors and from his vast correspondence with other scholars, statesmen, travellers, merchants and seamen. Mercator's early maps were in large formats suitable for wall mounting but in the second half of his life, he produced over 100 new regional maps in a smaller format suitable for binding into his Atlas of 1595.
context_section_description: In 1552 Mercator moved from Leuven to Duisburg in the Duchy of Cleves. He never gave his reasons for the move but several factors may have been involved: not having been born in Brabant he could never be a full citizen of Leuven; Catholic intolerance of religious dissidents in the Low Countries was becoming ever more aggressive and a man suspected of heresy once would never be trusted; the Erasmian constitution and the religious tolerance of Cleves must have appeared attractive; there was to be a new university in Duisburg and teachers would be required. He was not alone; over the years to come many more would flee from the oppressive Catholicism of Brabant and Flanders to tolerant cities such as Duisburg.
  The peaceful town of Duisburg, untroubled by political and religious unrest, was the perfect place for the flowering of his talent. Mercator quickly established himself as a man of standing in the town: an intellectual of note, a publisher of maps, and a maker of instruments and globes. Mercator never accepted the privileges and voting rights of a burgher for they came with military responsibilities which conflicted with his pacifist and neutral stance. Nevertheless, he was on good terms with the wealthier citizens and a close friend of Walter Ghim, the twelve times mayor and Mercator's future biographer.
  Mercator was welcomed by Duke Wilhelm who appointed him as court cosmographer. There is no precise definition of this term other than that it certainly comprehends the disciplines of geography and astronomy but at that time it would also include astrology and chronology (as a history of the world from the creation). All of these were among Mercator's accomplishments but his patron's first call on his services was as a mundane surveyor of the disputed boundary between the Duke's territory of the County of Mark and the Duchy of Westphalia.
  Around this time Mercator also received and executed a very special order for the Holy Roman Emperor a pair of small globes, the inner ("fist-size") Earth was made of wood and the outer celestial sphere was made of blown crystal glass engraved with diamond and inlaid with gold. He presented them to the Emperor in Brussels who awarded him the title Imperatoris domesticus (a member of the Imperial household). The globes are lost but Mercator describes them in a letter to Philip Melanchthon in which he declares that the globes were rotated on the top of an astronomical clock made for Charles V by Juanelo Turriano (Janellus). The clock was provided with eight dials which showed the positions of the moon, stars and planets. The illustration shows a similar clock made by the German craftsman Baldewein at roughly the same time.
  Earlier, Mercator had also presented Charles V with an important pamphlet on the use of globes and instruments and his latest ideas on magnetism: Declaratio insigniorum utilitatum quae sunt in globo terrestri : coelesti, et annulo astronomico (A description of the most important applications of the terrestrial and celestial globes and the astronomical ring). The first section is prefaced by Mercator's ideas on magnetism, the central thesis being that magnetic compasses are attracted to a single pole (not a dipole) along great circles through that pole. He then shows how to calculate the position of the pole if the deviation is known at two known positions (Leuven and Corvo in the Azores): he finds that it must be at latitude 73°2' and longitude 169°34'. Remarkably, he also calculates the longitude difference between the pole and an arbitrary position: he had solved the longitude problem—if his theory had been correct. Further comments on magnetism may be found in an earlier letter to Perrenot and on the later world map. In the Hogenberg portrait (below) his dividers are set on the position of the magnetic pole.
  In 1554 Mercator published the long-awaited wall map of Europe, dedicating it to his friend, now Cardinal, Antoine Perrenot. He had worked at it for more than twelve years, collecting, comparing, collating and rationalising a vast amount of data and the result 
caption: Mauretania in the 1578 Ptolemy
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