A correct understanding of the Earth’s magnetic field, or geomagnetism, is critical to both maritime navigation and orientation on land, as well as surveying and cartography.
There are two key variables of the Earth’s magnetic field that are vital to practical navigation and cartography. First, Magnetic Declination, or Magnetic Variation concerns the angle on the horizontal plane between the Magnetic North Pole or Magnetic South Pole (the places in the polar regions whereupon compasses point in their respective hemispheres), and True North (the direction along the meridian that leads to the North Pole). Naturally, the angle of declination changes depending upon one’s place on the globe, and as well varies over time, as the location of the Magnetic North continually shifts. Om maps, isogenic lines connect areas on the Earth’s surface where declination is constant at any given time. Since ancient times, societies had a rough working understanding of declination, but it was only during the Enlightenment that scientists lent it a precise definition and quantification.
Second, and related to declination, is Magnetic Inclination, or Magnetic Dip, which is the angle made with the horizontal by the Earth’s Magnetic Field lines, which varies at different points on the globe. As such, the dip is the angle made by the needle of vertically held compass, although this can only be precisely measured by an instrument known as a dip circle. The dip angle was discovered in 1544 by the German engineer Georg Hartmann, while the dip circle was invented in 1581 by the Englishman Robert Norman.
Mapping magnetic declination (and to a lesser extent, magnetic dip) became a major preoccupation of many of the greatest Enlightenment scientists and cartographers. The first proper magnetic declination map was Edmond Halley’s A New and Correct Chart, shewing the Variations of the Compass in the Western and Southern Oceans, as observed in ye year 1700 (London 1701), which shows isogenic line running across the Atlantic Ocean. This was followed by his geomagnetic world map, Nova & Accuratissima Totius Terrarum Orbis Tabula Nautica Variationum Magneticarum Index Juxta Observationes Anno 1700 (1702).
Other highlights of magnetic mapping during the 18th century were Leonhard Euler’s Tabula Geographica utriusque Hemisphaerii Terrestris exhibens declinationem acus magneticae pro singulis locis globi terraquei ad A.C. 1744 (1753); Johann Heinrich Lambert’s Vorstellung von der Abweichung der Magnetnadel für das Jahr 1770 (1777); Christian Amadeus Kratzenstein’s Mappa Exhibens Declinationes Acus Magnetiae ad initium Seculi decimi… M.DCCXCIII (1798); and the mapping contained in the work of the American luminary John Churchman’s The Magnetic Atlas, or Variation Charts of the Whole Terraqueous Globe (1790).
During the 19th century, gaining a precise understanding of the Earth’s magmatic field was complicated by the fact that there were several prominent competing theories as to the causes and nature of geomagnetism. As such, collecting empirical data in the field to support suppositions became a major preoccupation of exploring and scientific expeditions. Notably, the great Russian explorer Adam Johann von Krusenstern collected magnetic deviation readings from over 390 points during his 1803-6 circumnavigation. Importantly, the world’s greatest living explorer-scientist, Alexander von Humboldt, became the ‘godfather’ of geomagnetism studies and initiated and sponsored many seminal endeavours through the first half of the 19th century.
Enter Christopher Hansteen: The Great Norwegian Explorer of Geomagnetism
Christopher Hansteen (1784 – 1873) was a Norwegian geophysicist and astronomer who was long a dominant figure in scientific discourse in his native country, as well making discoveries of global significance. Born in Christiania (Oslo), he briefly joined the Danish Navy (Denmark then ruled Norway), but soon dropped out and found a new passion, eventually graduating with a mathematics degree from the University of Copenhagen.
In 1807, Hansteen commenced his lifelong obsession with discovering the true nature of the earth’s magnetic field. He developed a vast network of worldwide contacts to attain the best raw data and published a series of journal articles on the topic. His writings saw him being awarded a large research grant by Christiania’s Royal Frederick University, in 1811. In 1815, he became the editor of the Norwegian Almanac and the director of Christiania’s observatory. In 1816, Hansteen became a full professor of applied mathematics and astronomy at Royal Frederick University, and the following year was made the head of the Norwegian Mapping Authority. By this time, he was the foremost figure of the Norwegian scientific academia, giving him immense resources to pursue his geomagnetic passions.
Hansteen published his magnum opus, Untersuchungen über den Magnetismus der Erde, which included two parts, the Erster Theil. Die mechanischen Erscheinungen des Magneten and Anhang, enthaltend Beobachtungen der Abweichung und Neigung der Magnetnadel (Christiania: Jakob Lehmann und Chr. Gröndahl, 1819). In this brilliant treatise, Hansteen used fresh empirical data, including listings of declinations readings from 63 places in Russia, to expand upon his conceptions of the nature of terrestrial magnetism.
Importantly, Hansteen ascribed to the theory that there were four magnetic poles (North, South, East and West), although the occidental and oriental poles were not as strong as the others. However, we know today that there are only two magnetic poles (North and South), with the confusion being due to the great changes in deviation as one moves east or west, being an understandable misconception. However, this view did into invalidate the many good readings and analysis with regards to the North Magnetic Pole. Notably, Humboldt, and many other luminaries, also ascribed to the ‘four poles’ theory.
From 1828 to 1830, Hansteen led his own grand expedition to Siberia, a mission jointly sponsored by the Norwegian government and Alexander von Humboldt, whereupon he gathered 500 geomagnetic readings. In 1833, the founded a new observatory in Christiania, to which he added a special magnetic observatory six years later. He then spent the next four decades at the ‘elder statesman’ of Norway’s scientific community.
Hansteen’s Magnetic Atlas in Focus
As a companion to his Untersuchungen über den Magnetismus der Erde, Hansteen separately and privately published, the present Magnetischer Atlas gehörig zum Magnetismus der Erde, which featured 15 world maps of terrestrial magnetism printed on 7 plates (Tabulas). The maps were beautifully engraved in Stockholm, featuring the line ‘S. Anderson Sc. Stockh.’, in the lower margin, and were assembled and stitched together with a printed title, and issued in Christiania (Oslo). As a result, the Untersuchungen and the Magnetischer Atlas are today often not found together, with the atlas being a standalone publication.
Most of the maps are depict Abweichung (Magnetic Declination), with the isogenic lines taken at different historical times, which some showing arrows indicating the angles of deviations. Additionally, there are a couple maps showcasing Neigung (Magnetic Inclination).
It is worth nothing that the present example of the atlas is a stellar, unsophisticated example, uncut and sewn.
The present atlas is rare. While examples can be traced in several libraries in Europe, we can only trace a single institutional example in North America (held by the Harvard University Library). Moreover, we can trace only a single record for another example of the atlas as appearing on the market in recent years.
List of Plates:
No. I: Abweichungskarte für das Jahr 1600.
No. II: Abweichungskarte für das Jahr 1700.
No. III: Abweichungskarte für das Jahr 1756.
This plate features 3 Abweichungskarte (Magnetic Declination world maps), showing the varying isogenic lines, mitigated by the supposed four poles, as they were in the years 1660, 1700 and 1756.
No. IV: Abweichungskarte für das Jahr 1770.
No. V: Abweichungskarte für das Jahr 1710.
No. VI: Abweichungskarte für das Jahr 1720.
No. VII: Abweichungskarte für das Jahr 1730.
No. VIII: Neigungskarte für das Jahr 1700.
No. IX: Neigungskarte für das Jahr 1600.
This plate features 7 world maps, of which 4 (Nos. IV to VIII) are Abweichungskarte, showing the varying isogenic lines as they were in the years 1770, 1710, 1720 and 1730. Maps Nos. VIII and IX are Neigungskarte (Magnetic Inclination) maps showing the angle of the dip of the compass needle at various points in the world in the years 1700 and 1600.
No. X: Abweichungskarte für das Jahr 1800.
No. XI: Abweichungskarte für das Jahr 1744.
This plate features 3 Magnetic Declination world maps, showing the state of play in the years 1800 and 1744.
Polar Projection eines Segments der Nördlichen und Südlichen Halbkugel, zur. Aufklärung der Lage und Bewegung der Magnetpole vom Jahr 1600 bis 1800.
This is a double-hemisphere polar projection map of the world encompassing the globe from beyond latitude 40 degrees North and South and shows the angle of declination towards the North and South magnetic poles taken from various locations at different dates between 1600 and 1800, so seeking to ascertain the historical locations and movements of the poles.
Karte der beyden Halbkugeln welche den Magnetischen Aequator und die. Abweichungslinien für beyde Magnetaxen nach der ersten Eulerschen Theorie vorstellet.
Here is a double-hemispheres world map featuring isogenic lines according to the theories of Leonhard Euler.
Mappa Hydrographica sistens Declinationes Magneticas Anni 1787.
This World map on a Mercator Projection shows the isogenic lines as they were in 1787. Importantly, it features excellent data taken from 38 points all over the world, including Monterey, California, Quebec City, Quito, Bombay and Peking, with especially fine coverage in Russia, with readings taken in St. Petersburg, Arkhangelsk, Moscow, Guryev, Kazan, Ufa, Perm, Orenburg, Yekaterinburg, Barnaul, Tobolsk, Irkutsk and Yakutsk.
Mappa Hydrographica sistens Declinationes Magneticas Anni 1780.
Here is a World map on a Mercator Projection showing the isogenic lines as they were in 1780.
The present example of the atlas has a fine provenance, coming for the Library of Birr Castle, in County Offaly, Ireland, the seat of the Earls of Rosse. William Parsons, the 3rd Earl of Rosse (1800-67), was an esteemed astronomer who assembled a fine library on celestial matters and the earth sciences. He is most famous for constructing, on his estate, the ‘Leviathan of Parsonstown’, a six-foot refracting telescope that was the largest such instrument in the world for over 70 years.
References: Bibliothèque nationale de France: RP-12178; Harvard University Library: *QNC8.H1994.En819h (A) = atlas; OCLC: 457632659, 463200019, 82164083.