GERARDUS MERCATOR [latinized form of Gerhard Kremer] (1512–1594) was Flemish mathematician and geographer, was born at Rupelmonde, in Flanders, on the 5th of March 1512. Having studied at Bois-le-Duc and Louvain (where he matriculated on the 29th of August 1530, and became licentiate in October 1532), he met Gemma Frisius, a pupil of Apian of Ingolstadt, who at the request of the emperor Charles V. had settled in Louvain. From Frisius young Kremer derived much of his inclination to cartography and scientific geography.
In 1534 he founded his geographical establishment at Louvain; in 1537 he published his earliest known map, now lost (Terrae sanctae descriptio). In 1537–1540 he executed his famous survey and map of Flanders (Exactissima Flandriae descriptio), of which a copy exists in the Musée Plantin, Antwerp. At the order of Charles V. Mercator made a complete set of instruments of observation for the emperor's campaigns: when these were destroyed by fire, in 1546, another set was ordered of the same maker. In 1538 appeared Mercator's map of the world in (north and south) hemispheres, which was rediscovered in 1878 in New York; this work shows Ptolemy's influence still dominant over Mercatorian cartography.
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In 1541 he issued the celebrated terrestrial globe, which he dedicated to Nicolas Perrenot, father of Cardinal Granvelle: this was accompanied by his Libellus de usu globi, which is said to have been presented to Charles V. In 1551 a celestial globe followed. Mercator early began to incline towards Protestantism; in 1533 he had retired for a time from Louvain to Antwerp, partly to avoid inquiry into his religious beliefs; in 1544 he was arrested and prosecuted for heresy, but escaped serious consequences (two of the forty-two arrested with him were burnt, one beheaded, two buried alive). He now thought seriously of emigrating; and when in 1552 Cassandra, ordered by the duke of Juliers, Cleves and Berg to organize a university at Duisburg, offered Mercator the chair of cosmography the offer was accepted.
The organization of the university was adjourned, and never completed in Mercator's lifetime; but he now became cosmographer to the duke and permanently settled on the German soil to which many of his ancestors and relatives had belonged. Soon after this, however, he paid a visit to Charles V. at Brussels, and presented the emperor with a cosmos, a celestial sphere enclosing a terrestrial, together with an explanatory Declaratio: this work marks an era in the observation of longitude by magnetic declination, perfected by Halley. Charles rewarded the author with the title of imperatorii domesticus (Hofrath in the epitaph at Duisburg).
In 1554 Mercator published his great map of Europe in six sheets, three or four of which had already been pretty well worked out at Louvain; a copy of this was rediscovered at Breslau in 1889. Herein, though still greatly under Ptolemy's influence, Mercator begins to emancipate himself; thus Ptolemy's 62° for the length of the Mediterranean, reduced to 58° in the globe of 1541, he now cuts down to 53°. On the 28th of October 1556 he observed an eclipse at Duisburg; in 1563 he surveyed Lorraine, at the request of Duke Charles, and completed a map of the same (Lotharingiae descriptio); but it is uncertain if this was ever published. In 1564 he engraved William Camden's map of the British Isles; in 1568 he brought out his Chronologia, hoc est temporum demonstratio . . . ab initio mundi usque ad annum domini 1568, ex eclipsibus et observationibus astronomicis.
In the same year was published his memorable planisphere for use in navigation, the first map on" Mercator's projection," with the parallels and meridians at right angles (Nova et aucta orbis terrae descriptio ad usum nnvigantium accommodata). Improvements were introduced in this projection by Edward Wright in 1590; the more general use of it dates from about 1630, and largely came about through Dieppese support. In 1572 Mercator issued a second edition of his map of Europe; in 1578 appeared his Tabulae geographicae ad mentem Ptolemaei restitutae et emendatae; and in 1585 the first part (containing Germany, France and Belgium) of the Atlas, sive cosmographicae meditationes de fabrica mundi, in which he planned to crown his work by uniting in one volume his various detailed maps, so as to form a general description of the globe In 1585 he adapted his Europe to the Atlas; in 1587, with the help of his son Rumold, he added to the same a world-map (Orbis terrarum compendiosa descriptio), followed in 1590 by a second series of detailed maps (Italy, Slavonia, Greece and Candia).
The rest of the regional and other plans in this undertaking, mostly begun by Gerard, were finished by Rumold; they include Iceland and the Polar regions, the British Isles (dedicated to Queen Elizabeth), the Scandinavian countries (dedicated to Henr. Rauzovius), Prussia and Livonia, Russia, Lithuania, Transylvania, the Crimea, Asia, Africa and America (in the last Michael Mercator, in Asia and Africa Gerard Mercator the younger, assisted).
The designs are accompanied by cosmographical and other dissertations, some of the theological views in which were condemned as heretical (see the Duisburg edition ot 1594, folio). In 1592 Mercator published, two years after his first apoplectic stroke, a Harmonia evangeliorum. He died on the 5th of December 1594, and was buried in St Saviour's church, Duisburg. Besides his famous projection, he did excellent service with Ortelius in helping to free the geography of the 16th century from the tyranny of Ptolemy; his map and instrument work is noteworthy for its delicate precision and admirable execution in detail.
See the Vita Mercatoris by Gualterus Ghymnius in the Latin editions of the Atlas; Gérard Mercator, sa vie et ses uvres, by Dr J. van Raemdonck (St Nicolas, 1869); A. Breusing, Gerhard Kremer (Duisburg, 1878), and article" Mercator" in Allgemeine deutsche Biographie; General Wauwermans, 'Histoire de l'école cartographique belge . . . au XIV.-siècle, an article" Mercator" in Biographie nationale (de Belgique), vol. xiv. (Brussels, 1897). Also the lesser studies of Dr J. van Raemdonck, Sur les exemplaires des grandes cartes de Mercator; Carte de Flandre de Mercator; Relations entre . . . Mercator et . . . Plantin . . . (St Nicolas, 1884); La Géographie ancienne de la Palestine: Lettre de Gérard Mercator . . . mai 22, 1567 (St N., 1884); Les Sphères terrestre et céleste de Mercator, 1541 . . 1551 (St N., 1885); Van Ortroy, L'uvre géographique de Mercator.
1911 Encyclopædia Britannica, Volume 18. pg. 149-140.