MERCATOR, GERARDUS [latinized form of GERHARD KREMER] (1512-1594), Flemish mathematician and geographer, was born at Rupelmonde, in Flanders, on March 5, 1512. He studied at Bois-le-Duc and at Louvain where he met Gemma Frisius, a pupil of Apian of Ingolstadt, from whom he 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 1537-40 he executed his survey and map of Flanders (Exactissima Flandriae descriptio), of which a copy exists in the Musee Plantin, Antwerp. At the order of Charles V., Mercator made a complete set of instruments of observation for the emperor's campaigns. In 1538 appeared Mercator's map of the world in (north and south) hemispheres, rediscovered in 1878 in New York; this work shows Ptolemy's influence still dominant over Mercatorian cartography. 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. In 1533 Mercator 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. He now accepted in 1552 the chair of cosmography at the newly established Univer sity of Duisburg. The organization of the university was ad journed, and never completed in Mercator's lifetime; but he now became cosmographer to the duke and permanently settled on German soil. 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 explana tory 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 Mercator begins to emancipate himself from Ptolemy; 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 Oct. 28, 1556, he observed an eclipse at Duisburg; in 1563 he surveyed Lorraine, at the request of Duke Charles, and com pleted a map of the same (Lotharingiae descriptio) ; but it is un certain if this was ever published. In 1564 he engraved William Camden's map of the British Isles; in 1568 he brought out his Clironologia, 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 navigantium accom modate). Improvements were introduced in this projection by
Edward Wright in 1590; the more general use of it dates from about 163o, 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 meditations 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 under taking, mostly begun by Gerard, were finished by Rumold. The designs are accompanied by cosmographical and other disserta tions, some of the theological views in which were condemned as heretical. (See the Duisburg edition of folio.) In 1592 Mercator published, two years after his first apoplectic stroke, a Harmonic evangeliorum. He died on Dec. 5, 1594, and was buried in St. Saviour's church, Duisburg. With Ortelius he helped to free geography from the tyranny of Ptolemy; his map and instrument work is noteworthy for its delicate precision and admirable detail.
See the Vita Mercatoris by Gualterus Ghymnius in the Latin editions of the Atlas; Gerard Mercator, sa vie et ses oeuvres, by Dr. J. van Raemdonck (St. Nicolas, 1869) ; A. Breusing, Gerhard Kremer (Duis burg, 1878), and article "Mercator" in Allgemeine deutsche Biographie; General Wauwermans, Histoire de recole cartographique beige . . . au XVI.-siecle, and article "Mercator" in Biographie nationale (de Bel gique), 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 Geographie ancienne de la Palestine: Lettre de Gerard Mercator . . . may 22, 1567 (St. N., 1884) ; Les Spheres terrestre et celeste de Mercator, 1541 • • • 1551 (St. N., 1885) ; F. van Ortroy, L'Oeuvre geographique de Mercator; see the Vita Mer catoris by Gualterus Ghymnius in the Latin editions of the Atlas; J. van Raemdonck, Gerard Mercator sa vie et ses oeuvres (St. Nicolas, 1869), Sur les exemplaires des grandes cartes de Mercator; Carte d'e Flandre de Mercator, Relations entre Mercator et Plantin (1884), La Geographie ancienne de la Palestine: Lettre de Gerard Mercator (1884), Les Spheres terrestre et celeste de Mercator (1885) ; A. Breusing, Gerhard Kremer (Duisburg, 1878) ; F. van Ortroy, L'Oeuvre geographique de Mercator and H. Averdunk and J. Mueller-Reinhard, Gerhard Mercator (1914).