Gerardus Mercator


Born: 5 March 1512 in Rupelmonde, Burgundian Netherlands (now Belgium)
Died: 2 December 1594 in Duisburg, Duchy of Cleves (now Germany)


Gerard Mercator's parents were Hubert and Emerentia Kremer. Hubert Kremer worked the land and also was a cobbler, that is a shoemaker. Hubert and Emerentia were people of lowly status but Hubert had an brother Gisbert who had been educated at Louvain University and was a priest in Rupelmonde. It was in the hospice of St Johann in Rupelmonde, where Gisbert was a priest, that Gerard was born. He was the seventh child of Hubert and Emerentia who, a few weeks after the birth, returned to their home town of Gangelt.

For the first five years of his life Gerard and his parents lived in difficult conditions in Gangelt. The family income was insufficient to provide for more than the basic needs of life and most of their diet consisted of bread for they could afford little else. Hubert had leased a house in Rupelmonde in 1511, shortly before Gerard's birth, and in 1518 they journeyed from Gangelt to Rupelmonde to begin a new life. Gerard began attending school in Rupelmonde shortly after the family came to live there. At school he studied Latin, religion and arithmetic. By the time he was seven years old he was able to speak and to read Latin fluently.

Gisbert's influence meant that it was natural for Gerard and his brothers to aim at a career in the Church and indeed that was the route that his two eldest brothers took. Conditions in Rupelmonde began to deteriorate in the early 1520s, however, with huge increases in taxes to fund the war between the Habsburgs and France. The reformation, begun by Luther, escalated into revolution in 1525. The harsh times and the hard work that he put in to try to support his family took their toll on Hubert who died in 1526 or 1527. His brother Gisbert became Gerard's guardian.

Gisbert wanted the very best education possible for Gerard so in about 1527 he sent him to be educated with the Brethren of the Common Life in 'sHertogenbosch in the Netherlands. While Gerard was there his mother died and he chose a new name for himself. His name 'Kremer' means 'merchant' in German and he was sometimes known as 'Cremer' which is the Dutch equivalent. As a new name he chose Mercator, the Latin for 'merchant' and gave himself the full name of Gerardus Mercator de Rupelmonde.

On 29 August 1530 Mercator matriculated at the University of Louvain, taking the course in the humanities and philosophy. He studied at the Castle, one of four teaching houses of the university which offered two year Arts degrees based almost entirely on the teachings of Aristotle. He graduated from Louvain with a Master's Degree in 1532 and chose not to proceed to a higher degree. Already he felt that he wanted to challenge the views of Aristotle, yet this was as heretical at Louvain at that time as challenging the views of the Catholic Church.

After graduating, Mercator began to have serious worries on how to reconcile the account of the origin of the universe given in the Bible with that given by Aristotle. He wrote later (see for example [12]):-

But when I saw that Moses' version of the Genesis of the world did not fit sufficiently in many ways with Aristotle and the rest of philosophers, I began to have doubts about the truth of all philosophers.

This almost certainly explains why he chose to leave the university rather than study for a higher degree, since he had already decided that he did not want to become a philosopher. He travelled to a number of places while going through this personal crisis including Antwerp and Mechelen. His travels did little for his religious worries but gave him a deep interest in geography which he saw at the subject which could best explain the structure of the world which God created.

Mercator returned to Louvain in 1534 where he now studied mathematics under Gemma Frisius. However, not having any background in the subject, Mercator soon found that the mathematics courses beyond him. Realising that Mercator wanted to learn mathematics to apply it to cosmography, Gemma Frisius gave him advice on the best route into learning the mathematics he needed to know, giving him books to study at home. Once put on the right path by Gemma Frisius, Mercator quickly progressed in understanding and enjoyment of mathematics. He also learnt about applications of mathematics to geography and astronomy which he found "extremely agreeable". He later wrote (see for example J Babicz in [10]):-

Since my youth geography has been for me the primary object of study. When I was engaged in it, having applied the considerations of the natural and geometric sciences, I liked, little by little, not only the description of the earth, but also the structure of the whole machinery of the world, whose numerous elements are not known by anyone to date.

Mercator learnt to be an engraver and instrument maker at this time from Gaspard Van der Heyden (also known as Gaspar à Myrica). However at this time Mercator was not only was learning, he was also teaching. He earned a steady income giving mathematics tuition to the students at Louvain, obtaining permission from the university to do this. He also earned extra money by making mathematical instruments of exceptional quality which he sold.

In 1535-1536 Mercator, working in Louvain with Van der Heyden and with Gemma Frisius, constructed a terrestrial globe. The globe had been commissioned by the Emperor Charles V to (see for example [11]):-

... make mathematics more illustrious ... keep alive the memory of old kingdoms and events and ... make known to coming generations our time and our realm in which ... very many islands and areas unknown in earlier centuries have been discovered ...

The paper strips which were printed for the globe were printed using copper rather than wood blocks, the first to be printed using that substance. The geographical work was mainly due to Gemma Frisius while Mercator's role was that of an engraver. With copper rather than wood on which to engrave place names, names of regions and geographical descriptions, the printed globe contained vastly more information than any that had previously been constructed.

In September 1536 Mercator married Barbara Schelleken and their first child, a son Arnold, was born on 31 August 1537. They had six children, thee daughters and three sons. In 1537 Mercator, working with Van der Heyden and with Gemma Frisius, constructed a globe of the stars. This time Mercator and Van der Heyden appeared as more equal collaborators with Gemma Frisius with the globe claiming that is was made by (see for example [11]):-

Gemma Frisius, doctor and mathematician, Gaspard Van der Heyden and Gerard Mercator of Rupelmonde.

Mercator produced his first map, which was one of Palestine, in 1537 [6]:-

Mercator knew Palestine better than any place outside the Low Countries. He had grown up with its miracles and revelations. He knew its history. Palestine had been the subject of the first map that most of his generation had ever seen. And like the Bible maps of his boyhood, his would show the route described in the Fourth book of Moses.

The first map of the world to be produced by Mercator used a projection due to Oronce Fine and appeared in 1538. This map is notable for being the first to represent America as stretching from the northern regions to the southern regions and for giving North America that name.

The map of Flanders which Mercator produced in 1540 was commissioned for political purposes. It must be realised that maps can send important signals about the regions which they cover, and the existing map of the region emphasised Ghent at the expense of Antwerp and other towns. It suggested an independent Flanders and Mercator's map was commissioned to correct this impression. In fact Mercator produced a map of high accuracy using data from a survey of Flanders carried out using the method of triangulation described by Gemma Frisius.

Mercator had a long term plan of producing a world map by producing individual maps of the different regions. As part of this project he set to work on the map of Europe in the summer of 1540. There were many problems with a world map, however, for the rapid increase in information coming from exploration of the Earth meant that maps rapidly became outdated. Also contradictory information was often given from inaccurate surveys leaving the mapmaker with the almost impossible task of deciding which data was correct. Mercator realised the reason for some of the incorrect data; sailors assumed that following a particular compass course would have them travel in a straight line whereas this was untrue. He realised that a ship sailing towards the same point of the compass would follow a curve called a loxodrome (also called a rhumb line or spherical helix), a curve recently studied by Pedro Nunes who was a mathematician greatly admired by Mercator. A new globe which he produced in 1541 was the first to have rhumb lines shown on it.

Mercator was arrested in February 1544 and charged with heresy. This was partly due to his Protestant beliefs, partly due to the fact that he travelled so widely to acquire data for his maps that suspicions were aroused. He spent seven months in prison in Rupelmonde castle. Others that were arrested at the same time admitted that they did not believe that the body of Christ was physically present in the communion host and they did not believe in purgatory. They were burned at the stake or buried alive. Nothing was found to connect Mercator with the others 'heretics' even after they had been tortured. Mercator's house was searched and his belongings confiscated but nothing incriminating was found to show that he was anything other than a good Roman Catholic.

He was released from prison in September 1544, mainly due to strong support from the University of Louvain. After his release he returned to his family in Louvain but their financial position was by now dire. It is likely that he was forced to pay for the cost of his own imprisonment as many were at this time. He worked hard on constructing mathematical instruments that he has promised to construct before his arrest. John Dee arrived in Louvain in 1548 and quickly became friends with Mercator. Dee, who spent three years working with Mercator, later wrote:-

It was the custom of our mutual friendship and intimacy that, during three whole years, neither of us lacked the other's presence for as much as three whole days.

During this time Mercator worked on a celestial globe of the same size as his terrestrial globe of 1541 which he completed in 1551. The positions of the stars were corrected to their positions in 1550 using Copernicus's model of the universe. In 1552 Mercator moved to Duisburg where he opened a cartographic workshop. The fact that a new university was planned for the town meant that he anticipated a ready demand for maps, books, globes and mathematical instruments.

In Duisburg Mercator completed his project to produce a new map of Europe by October 1554. It was a large map, 1.6 metres by 1.3 metres, drawn using a new projection devised by Johannes Stabius. This re-established Mercator as the leading European map maker and, as well as praise for its scholarly value, the map had considerable commercial value. His income secure, Mercator and his family moved into a large house in the wealthiest district of Duisburg. He was described by a friend at this time (see [9]):-

Although he ate and drank very little, he kept an excellent table, well furnished with the necessities of civilised living... He always did his best to help those who were poor and less fortunate than he and ... he cultivated and cherished hospitality. Whenever he was invited by the magistrates to a banquet or by friends to a dinner, or he himself invited friends, he was invariable cheerful and witty ...

He taught mathematics in Duisburg from 1559 to 1562 in a new school designed to prepare students for entry into the proposed new university. When plans for the university were scrapped in 1562, Mercator ended his teaching duties at the school handing them over to his second son. Further maps followed; one of Lorraine in 1564 and one of the British Isles in 1564. Like some previous commissions, these maps were required for political ends, the latter map being sought as a Catholic map to be used against the Protestant Queen Elizabeth.

Mercator was appointed Court Cosmographer to Duke Wilhelm of Cleve, also in 1564. During this period he began to perfect a new map projection for which he is best remembered. The 'Mercator projection' that bears his name was first used by him in 1569 for a wall map of the world on 18 separate sheets entitled:-

New and more complete representation of the terrestrial globe properly adapted for its use in navigation.

The 'Mercator projection' had the property that lines of longitude, latitude and rhomb lines all appeared as straight lines on the map. He had, he wrote on the map:-

... spread on a plane the surface of a sphere in such a way that the positions of all places shall correspond on all sides with each other both in so far as true direction and distance are concerned and as concerns true longitudes and latitudes.

He was also the first to use the term 'atlas' for a collection of maps. He used the word atlas:-

... to honour the Titan, Atlas, King of Mauritania, a learned philosopher, mathematician, and astronomer.

Mercator published corrected and updated versions of Ptolemy's maps in 1578 as the first part of his 'atlas'. His 'atlas' continued with a further series of maps of France, Germany and the Netherlands in 1585. Although the project was never completed Mercator did publish a further series in 1589 including maps to the Balkans (then called Sclavonia) and Greece.

On 5 May 1590 Mercator had a stroke which left his left side paralysed. Frustrated that he could no longer work, he slowly recovered but suffered great frustration at his inability to continue his map making projects. By 1592 he was able to do a small amount of work again but his eyes were by now almost blind. He had a second stroke towards the end of 1593 which took away his power of speech and although he fought bravely, recovering some power of speech, a third stroke was too much for the old man. Some maps which were incomplete at his death were completed and published by his son in 1595.

Mercator's break from the methods of Ptolemy was as important for geography as was Copernicus for astronomy.

Article by: J J O'Connor and E F Robertson

August 2002


MacTutor History of Mathematics
[http://www-history.mcs.st-andrews.ac.uk/Biographies/Mercator_Gerardus.html]