Naval interests and polar pursuits

Initially, Hansteen had no specific orientation towards Britain. His main inspiration was Alexander von Humboldt, a Prussian natural historian working in Paris, and Hansteen's first publications on terrestrial magnetism appeared in French and in German.Footnote ⁸ Encouraged by Örsted, Hansteen published his work in German in 1819, and he wrote letters introducing the book and atlas to leading Continental researchers on terrestrial magnetism.Footnote ⁹ Meanwhile, in Paris, Hansteen's University of Christiania colleague, physicist and chemist Jens Jacob Keyser, introduced Hansteen's book and atlas to Alexander von Humboldt, who was clearly impressed.Footnote ¹⁰

The only person in Britain Hansteen approached in early 1819 was Thomas Thomson, medical doctor, chemist, mineralogist and founding editor of the Annals of Philosophy. Thomson had seen an announcement of Hansteen's book in a German periodical and in 1818 informed readers of his journal that Hansteen's forthcoming Researches on the Magnetism of the Earth should be greatly interesting in Britain because ‘magnetism has of late years been so much neglected in this country’.Footnote ¹¹ After receiving a copy from Christiania, Hansteen's Magnetismus der Erde was introduced in subsequent volumes by Thomson to British audiences among contributions from Örsted and Faraday.

Melting Arctic ice changed everything. In 1817, whaler and Arctic expert William Scoresby of Whitby reported that ‘a remarkable diminution of the polar ice had taken place’ on Greenland's east coast.Footnote ¹² This immediately aroused interest from Joseph Banks at the Royal Society and John Barrow at the Admiralty, resulting in renewed Arctic exploration efforts. Also, when the existing Discovery of a Northwest Passage Act from 1744 was repealed by the Longitude Act in 1818, a closer relationship was established between Royal Society experimentalists and Royal Navy navigators. One direct result was the two British expeditions towards a northwest passage in 1818 and 1819.Footnote ¹³ New interest in Arctic voyages and polar pursuits also led to revived interest in terrestrial magnetism: ‘The roots of the magnetic crusade may be traced to 1819, when Edward Sabine and James Ross were taking magnetic measurements in Baffin's Bay as part of the scientific work of Parry's Arctic voyage in search of a northwest passage.’Footnote ¹⁴

In Britain, this changing climate created new alliances between military and scientific personnel, resulting in new prestige and recognition for practical skills in precision measurements. A shift of power and relevance occurred between academic mathematicians in the ‘Cambridge network’ and the ‘mathematical practitioners’ in the Royal Military Academy and the Royal Military College. Also, a third group of ‘scientific servicemen’ emerged among armed services members increasingly engaged in scientific work on various voyages of discovery, exploration and survey associated with the Admiralty Hydrographic Office, the Royal Artillery or the Royal Engineers, such as hydrographer Francis Beaufort, or officers and explorers like Edward Sabine, Basil Hall and Henry Foster.Footnote ¹⁵ Many of Hansteen's British supporters were among this latter group of scientific servicemen. Most important was Edward Sabine of the Royal Artillery, appointed by the Royal Society to make scientific observations and experiments on the two Arctic voyages in 1818 and 1819.Footnote ¹⁶

Hansteen was well informed about the 1818 expedition, where John Ross took HMS Isabella and HMS Alexander into Baffin Bay near the magnetic pole while observing a magnetic variation or westward declination of 89° and a dip or inclination of 84° 40′. He also knew about the proposed 1819 expedition, in which William Edward Parry led a second voyage seeking a northwest passage.Footnote ¹⁷ In spring 1819, Hansteen began courting this new British audience, and he sent his book and atlas to Sir Joseph Banks, the aged president of the Royal Society, urging him to ensure that Parry would take them on his voyage, departing in summer. Only later in 1819 did Banks reply, apologizing that he had been unable to get them on board: ‘I regret much to tell you, that it did not reach my hands untill after the Expedition to Baffin bay had sailed which prevented me from furnishing them with your book and maps’.Footnote ¹⁸

In summer 1819, Hansteen travelled to London to purchase various scientific instruments and to promote his recently published work.Footnote ¹⁹ He regularly visited the Royal Institution's library, and he gave mathematician Charles Babbage a copy of Magnetismus der Erde.Footnote ²⁰ Most importantly, however, he became acquainted with John Barrow at the Admiralty and Thomas Henniford Hurd at the Hydrographical Office, who introduced Hansteen to a wide network of naval officers and scientific servicemen.Footnote ²¹ Barrow became a strong Hansteen supporter and eventually he forwarded Hansteen's studies and charts to the Board of Longitude in 1827.Footnote ²²

Hansteen also had a reputation in Edinburgh, where David Brewster, editor of the Edinburgh Philosophical Journal and the Edinburgh Encyclopedia, introduced his work in Scotland.Footnote ²³ In the first volume of the Edinburgh Philosophical Journal (1819), among accounts of the Ross and Parry expeditions and other contributions by Scoresby, Hansteen's work was introduced in a comprehensive and unsigned article actually written by Thomas Carlyle, a young mathematics teacher and later rector of Edinburgh University.Footnote ²⁴ According to Brewster, Hansteen had predicted the position of the magnetic pole, which happened to be a goal of the Parry expedition in 1819. After their return in 1820, Brewster published an account of their polar endeavours and scientific results, which he forwarded to Hansteen in Christiania with the compliment that Parry, sometime between 23 and 28 August 1819, must have passed just north of Hansteen's predicted position of the magnetic pole. In turn, Brewster's information enabled Hansteen to utilize the new results from Sabine to make magnetic maps and visualize the magnetic pole's location with surrounding isoclinic lines. Meanwhile, Brewster published in the Edinburgh Philosophical Journal a modified version of Hansteen's magnetic chart of the needle's variations and dip.Footnote ²⁵

Hansteen's magnetometer

While in 1819 Hansteen received a breakthrough in Britain promoting Magnetismus der Erde, the year also marked a major shift in Hansteen's own approach towards studying terrestrial magnetism. The analysis in his book was based on written sources: a variety of observational reports in ships’ logs, notebooks, navigation treatises and travel literature, from Robert Norman's The Newe Attractive (1581) and William Gilbert's De Magnete (1600) to the late eighteenth-century voyages of James Cook and Alexander von Humboldt – 140 pages with tables of declination and inclination were added as an appendix.

Neither the book nor the accompanying atlas contained any systematic approach to studying magnetic intensity. To be sure, both Charles-Augustin de Coulomb and Henry Cavendish had previously measured intensity with either a suspended or a pivoted needle oscillating horizontally.Footnote ²⁶ However, their observations were limited to a short time span and could not account for daily or secular variation. Also, the observations were limited to a single place, either Paris or London, and could not account for how intensity changed from place to place. Thus, Hansteen argued, hardly any relevant series existed apart from Humboldt's magnetic observations across the Atlantic in 1799 and Sabine's measurements of magnetic intensity in North America of 1818 and 1819. A remaining problem was the needle's own magnetization which gradually declined over time and thus changed from place to place, further complicating exact measurements of magnetic intensity.

In 1819, Hansteen began observing systematically the monthly and daily variation of magnetic intensity using a new scientific instrument usually described as ‘Hansteen's magnetometer’. His main contribution consisted of constructing a small, portable magnetometer with a horizontally suspended needle, an instrument which was later multiplied and distributed to other observers.Footnote ²⁷ Thus Hansteen's portable apparatus ‘became the favourite intensity-measuring apparatus for travellers’.Footnote ²⁸ And as it became widely adopted, numerous observers and researchers had to subscribe to Hansteen's system and standards when reporting their results. Thus Hansteen established a method ‘that was to be standard for decades’.Footnote ²⁹ This circulation of Hansteen's magnetometers and techniques made possible – probably for the first time – systematic measurements of magnetic intensity at widely separated places, using a standard scientific instrument, standard observation methods, and standard mathematical formulae for manipulation and reduction: ‘He called it a magnetometer (perhaps the first use of this word). He also standardized the technique, taking the time required for three hundred oscillations of a suspended needle as the measurement of the earth's magnetic intensity at a given location’.Footnote ³⁰ This standardization process was crucial in developing international cooperation in studying terrestrial magnetism.

Hansteen's magnetometer was built by Henrik Clausen, instrument-maker at the university in Christiania, who became the first director of the Norwegian Bureau of Weights and Measures; Hansteen and close colleagues would properly refer to it as ‘Clausen's instrument’. Further, Hansteen credited Peter Johan Wleugel with inspiring the instrument's development; Wleugel was a leading scientific serviceman in Copenhagen – Royal Danish Navy commander, Royal Naval Academy examiner, navigation director – and one of two witnesses at Örsted's famous experiment when discovering electromagnetism in 1820. Wleugel had systematically studied variation and inclination since 1805; published a paper in Brewster's Edinburgh Philosophical Journal; and, in correspondence with Hansteen from 1817 to 1819, made valuable suggestions concerning how to construct a magnetometer with a horizontally suspended needle.Footnote ³¹

Hansteen's magnetometer was a small wooden box with glass viewing panels and a thermometer inside. On the top was a wooden pillar, and inside the pillar a silk fibre (150 millimetres long) which suspended a horizontal magnetized cylinder vibrating freely within the box. It had a tripod stand, levelled by foot screws, for field observations. When the instrument was placed in the magnetic meridian, a knife or a piece of metal set the magnet in motion, and it vibrated back and forth over a circle on paper graduated into degrees. The time required for three hundred oscillations (twelve to sixteen minutes) was used as the measure of the magnetic force's intensity.

Still, the most important part was the magnetized cylinder. Because most magnets lost strength over time, it became crucial to measure the cylinder's changing strength, too. The practical problem increased because different needles lost strength at different rates, so all had to be constantly checked, controlled and compared. Crucially, on his summer trip to London in 1819, Hansteen acquired a needle (72.8 millimetres) of remarkably steady magnetism from John Dollond; as hard ‘as fire and water can make it’.Footnote ³² As late as June 1834, Hansteen explained to Örsted how the magnetization had in fact remained unchanged over fourteen years.Footnote ³³ Just as the metre prototype in Paris became the international standard for measuring length, Dollond's cylinder in Christiania became Hansteen's standard against which all observations of magnetic intensity had to be calibrated. The system's integrity rested on the needle's stability. Hansteen in Christiania coordinated the circulation of wooden boxes and magnetized needles and controlled the results through a series of mathematical reductions to the Dollond cylinder.

Figure 2.

Hansteen's magnetometer. Norwegian Museum of Science and Technology, NTM 9424.

Hansteen began making magnetic measurements on his 1819 London trip, but interestingly he took a quick detour to Paris. His aim and ambition were all too apparent. By observing the intensity in the two capitals, Humboldt's incommensurable series from Paris to Peru and Sabine's series from Britain to Baffin Bay were suddenly compatible, but only in accordance with Hansteen's system and standards. Further, during various journeys between 1820 and 1824, Hansteen made lengthy observations at thirty-seven stations in Norway, Sweden, Denmark and northern Europe. His results were published with a detailed description of the magnetometer in the Magazin for Naturvidenskaberne and the Annalen der Physik und Chemie.Footnote ³⁴ Further, Hansteen trained students and colleagues to make observations following his techniques and standards. Most importantly, his Danish mentor Örsted took a Hansteen magnetometer on his triumphant journey to France and Britain in 1822 and 1823.Footnote ³⁵ Having first made observations with physicist Paul Ermann in Berlin, Örsted also collaborated with Arago in Paris, and, as the instrument crossed the Channel a second time, Hansteen's methods of measuring magnetic intensity were introduced by Örsted to several British scientific practitioners and servicemen. In London, Örsted was accompanied by Henry Kater; in Liverpool, Örsted introduced Thomas Stewart Traill to Hansteen's magnetometer; and in Edinburgh, Örsted made observations with David Brewster. The results were collected and calculated by Hansteen in Christiania and published in the Magazin for Naturvidenskaberne and the Annalen der Physik und Chemie in 1825 with Hansteen's first – and what is usually regarded as the first – printed chart of isodynamic lines displaying the distribution of magnetic intensity (horizontal component only) covering southern Scandinavia, parts of the British Isles, and northern Europe.Footnote ³⁶

By then, Brewster had published in the Edinburgh Philosophical Journal a series of results from observations made by Hansteen with his magnetometer over 1819 and 1820. Brewster also reproduced Hansteen's letter to astronomer Carl Ludwig Rümker, director of Hamburg's Nautic Academy, containing more results and a detailed description of the instrument and the method.Footnote ³⁷ Because Rümker was soon to depart for New South Wales, Brewster invited Hansteen to continue communicating directly with him: ‘The continuance of your communication would be extremely gratifying to me, and it would give me the greatest pleasure if I could be of any service to you in return.’Footnote ³⁸

The rape of Sabine

Edward Sabine, later to emerge as the leader of the magnetic lobby, was still unaware of Hansteen's work on terrestrial magnetism. In 1821, he received the Royal Society's Copley Medal for his magnetic research, one year after Örsted.Footnote ³⁹ In 1822, he joined HMS Pheasant on a pendulum expedition south to Bahia, Brazil, and in 1823 he sailed on HMS Griper north to Spitsbergen. The pendulum observations had priority on both voyages, but Sabine also made valuable magnetic observations, and his combined results were published as An Account of Experiments to Determine the Figure of the Earth, printed in 1825 with funding from the Board of Longitude.Footnote ⁴⁰ Crucially, on the latter voyage, Sabine visited Norway, and in September 1823 he established a small observatory in Hammerfest to make magnetic measurements.Footnote ⁴¹ Meanwhile, between 1821 and 1823, Parry led his second voyage for the discovery of a north-west passage with HMS Hecla and HMS Fury, this time through the Hudson Strait, but was unable to locate the magnetic pole. The expedition's results were published in 1824, and Hansteen immediately used the recent observations of inclination to pinpoint more precisely the magnetic pole's location.Footnote ⁴² Soon, he would also appropriate the results from Sabine.

Sabine first approached Hansteen in autumn 1825 and forwarded a recent publication: ‘Captain Sabine hopes that his work will be read with interest by Professor Hansteen; and particularly the part which relates to the magnetic Intensity of the Earth’.Footnote ⁴³ Hansteen replied in December and sent Sabine a copy of his recent paper on magnetic intensity, including the map with isodynamic lines. Now Hansteen suggested to Sabine that he should conduct a magnetic survey in Britain like Hansteen had done in Scandinavia: ‘A Series of Observations with respect to intensity and dip throughout England and Scotland would be of considerable interest, and I should wish, that You or another good observator would perform this charge.’Footnote ⁴⁴ Flattered, and upon Hansteen's request, Sabine sent him a copy of An Account of Experiments.Footnote ⁴⁵

By February 1826 Hansteen took control of Sabine's results: first, by challenging the instrument and the methods Sabine used; second, by reducing Sabine's numbers in accordance with his own system and standards.Footnote ⁴⁶ For instance, he categorically claimed that any observation of intensity using an inclinometer, measuring the vertical component of the magnetic force's total intensity, would be futile in the Arctic regions because of friction upon the axis and the difficulty of separating the magnetic force from the force of gravity. Yet, on the 1823 expedition to Spitsbergen, Sabine had also made observations in the horizontal plane with a vibrating magnetic needle suspended by a silk thread inside an octagonal mahogany box with glass panels for reading the results – very similar to Hansteen's magnetometer. Sabine's instrument seemed much too large, rather unpractical and quite unsuitable for expeditions on land, Hansteen argued, in comparison with his own small and portable magnetometer.

Hansteen also criticized as unstable the six needles Sabine used: ‘Your horizontal needles have not been quite invariable, and methinks of too great dimensions.’ In particular, he challenged Sabine's results when using a needle from Henry Browne – a fellow of the Royal Society of London and Sabine's brother-in-law – which according to Hansteen's calculations was proven totally unreliable: ‘That Mr. Browne's needle also has varied is evident.’ More crucially, Hansteen pointed to Sabine's lack of a standard for comparison and calibration similar to his own Dollond cylinder: ‘I have a cylinder, made by Dollond in Aug. 1819, which in these 6 years has not varied 1/10 of a second upon 300 vibrations … from the end of 1819 to this day.’ Hansteen also accused Sabine of failing to measure the values of his various magnets both before and after the expeditions to determine their gradual loss of strength, thus making the whole series of observations unreliable.Footnote ⁴⁷ In short, Hansteen picked apart Sabine's apparatus and authority.

Having challenged the instrument's reliability and the needles’ stability, Hansteen went further by taking control of Sabine's recent results, just as he previously had reduced the values from Humboldt and Sabine to his own system by visiting London and Paris in 1819. In 1823, Sabine had visited both Trondheim and Hammerfest in Norway, and Hansteen immediately organized two different expeditions to reclaim these grounds. First, he visited Trondheim on his trip around the Gulf of Bothnia, and second, Hansteen sent Lieutenant Colonel Meilænder and Lieutenant Palludan to Finnmark in northernmost Norway to make measurements at Hammerfest on their journey to the Kola Peninsula.Footnote ⁴⁸ With both Trondheim and Hammerfest as common stations for observations, Hansteen could now tap into and translate all observations from Sabine's expedition in 1823, as Sabine later explained, ‘and he was thereby enabled to compute the values of the intensity at all the stations visited by me, relatively to the force at Drontheim, which he had already compared with Paris by observations at Drontheim and Christiania, and at Christiania and Paris’.Footnote ⁴⁹

While contesting Sabine's method and magnetometer, Hansteen made the most of Sabine's observations. His magnetic measurements reaching from Bahia at 13° south latitude to Spitsbergen at 80° north latitude were now commensurable with Hansteen's numerous observations in Scandinavia and northern Europe. Further, Sabine's voyage to Brazil in 1822 also established a link to Humboldt's earlier observations across the Atlantic in 1799 due to the shared stations at Tenerife and Trinidad. Hansteen could now summarize Sabine's results together with his own observations and in accordance with Humboldt's concept of ‘total magnetic force’, a concept which also took into account the direction of the force (or the dip of the needle) as measured with an inclinometer. In a new magnetic chart from 1826 displaying the total magnetic force's isodynamic lines, Hansteen managed to reduce the results from Humboldt and Sabine to his own system through mathematical manipulations, ultimately compared and standardized to his Dollond cylinder.Footnote ⁵⁰

After so brutally treating Sabine, Hansteen attempted reconciliation: ‘I have a little magnetic cylinder destined for You, which I will send You next Summer when I am assured of its invariability’.Footnote ⁵¹ Sabine soon received needles and magnetometers from Hansteen and became one of his strongest supporters in Britain. Also, while Sabine had initially subscribed to the Earth's having only two magnetic poles – his magnetic chart in his 1825 publication revealed only one pole in the northern hemisphere near Baffin Bay – he now ardently supported Hansteen's four-pole theory of terrestrial magnetism.Footnote ⁵²

Sabine's contribution

Early in 1826, Sabine received Hansteen's letter, delivered by Lieutenant Erichsen of the Norwegian Navy. Erichsen had supplied Hansteen with magnetic measurements of declination and inclination since 1819 and brought the magnetometer as far south as Breslau (Wrocław) in summer 1824. He introduced Sabine to the apparatus he had brought along to observe for Hansteen while in England. Erichsen also attracted the interest of Lieutenant Henry Foster at the Royal Greenwich Observatory, who had accompanied Sabine on the 1823 expedition to Norway, Spitsbergen and Greenland and more recently had measured magnetic intensity on Parry's north-west passage expedition with HMS Hecla in 1824–1825. After Erichsen's lobbying in London during spring 1826, Hansteen sent two other magnetometers and four magnetic cylinders to Sabine: one box for Sabine and one for Foster. Sabine was instructed to make observations in Regent's Park, London, at the place where Örsted and Kater had observed in 1823, while Foster was supposed to make observations for Hansteen on his forthcoming round-the-world voyage.Footnote ⁵³

Meanwhile, Foster's great expedition was temporarily postponed, Sabine informed Hansteen in summer 1826, as ‘the good understanding which did prevail between our Board of Admiralty & the Royal Society, has, it is said, been temporarily interrupted’.Footnote ⁵⁴ Meanwhile, Foster received the 1827 Copley Medal for his magnetic research and other observations during the Arctic expedition to Port Bowen, and the same year he joined the British naval north polar expedition, captained by Parry, reaching a new farthest-north record of 82° 45′ north in 1827. Finally, in 1828 he captained the British naval expedition to the South Atlantic on HMS Chanticleer before drowning in a Panamanian river in 1831. According to Miller, ‘Foster's voyage epitomized the coming together of scientific servicemen, mathematical practitioners, and members of the Cambridge network in the common cause of promoting the geophysical sciences’.Footnote ⁵⁵ In the late 1820s, Hansteen and Sabine shared their common excitement over Foster's great expedition, but no magnetic results ever reached Hansteen in Christiania.

With Foster temporarily out of the loop in 1826, Sabine decided to keep the two apparatuses from Hansteen and establish a slightly different scheme. Using the magnetometer that Hansteen had personally given him, Sabine conducted observations around London, both in the Horticultural Society's garden at Chiswick in December 1826 and in Shernfold Park near Royal Tunbridge Wells in Kent in January 1827. He sent the other apparatus to Edinburgh, where the Royal Navy's Captain Basil Hall conducted experiments assisted by Lieutenant Robert Craige in February 1827. Sabine then took his own apparatus to Paris, where he observed in the Royal Observatory's garden assisted by William Ritchie. As the apparatuses travelled around, so did the four magnetic needles from Hansteen (Nos IV, VIII, X and XI) along with two more (A and B) made by Dollond on Sabine's request ‘of the same size and form as those sent me by Professor Hansteen’.Footnote ⁵⁶ In a complicated scheme of travel and circulation, Sabine constantly cross-checked and calibrated the magnetic needles before publishing his results in Philosophical Transactions (1828), where he described Hansteen's magnetometer and methods of observation and calculation. Yet Sabine remained totally dependent upon Hansteen's mathematical reductions, for instance, to handle temperature variation.Footnote ⁵⁷ And the cylinders that travelled between Paris and London had to be returned to Hansteen in June 1827 for comparison with the Dollond cylinder to determine accurately the magnetic intensity in Paris, London and Christiania.

Hansteen's magnetometers travelled even more extensively, and, as it became accepted as a standard instrument, it was also replicated, modified and manufactured by others. For instance, Sabine forwarded one of his two boxes to Jean-Nicolas Nicollet at the Paris observatory, who intended to take it on a mountain expedition in Savoy. Meanwhile, Arago in Paris made another apparatus with six needles, Sabine explained to Hansteen, ‘on the same plan as yours, but the needles about an English inch longer’, to accompany Jules de Blosseville, who sailed on the French Navy corvette La Chervette from Toulon for the East Indies in May 1827.Footnote ⁵⁸ Similarly, in Brussels, Sabine introduced Hansteen's magnetometer to Adolphe Quetelet, Royal Observatory director, who immediately built an apparatus on Hansteen's model. He began determining the relative magnetic intensity of Brussels compared to London and Paris, before travelling with the magnetometer through the Netherlands and Germany (1829) and to Switzerland and Italy (1830), constantly measuring intensity according to the method derived from Hansteen and described by Sabine in the Philosophical Transactions (1828).Footnote ⁵⁹

Hansteen's magnetometer even crossed the Atlantic. Since 1827, Joseph Henry had been fascinated by Hansteen's aurora borealis work speculating about possible links to electromagnetism.Footnote ⁶⁰ He was recruited by Professor James Renwick at Colombia College (New York), who during summer 1830 had received from Sabine a magnetometer and one of Hansteen's original cylinders (No XI) together with one of Sabine's own needles from Dollond,

In September 1830, Henry made observations with Hansteen's magnetometer to determine magnetic intensity in Albany.Footnote ⁶²

Initially, Sabine had forwarded Hansteen's magnetometer to Renwick for a different purpose; that is, the proposed expedition prepared by the US government for scientific research in the southern hemisphere (eventually the Wilkes Expedition of 1838–1842). This would be a wonderful occasion to observe near one of the magnetic south poles, Sabine argued convincingly. Wilkes was to be trained in magnetic observations with Hansteen's magnetometer forwarded to him in August 1833 by Henry on the orders of Wilkes's brother-in-law, Professor Renwick: ‘Be so good as deliver to the order of Lt. Charles Wilkes Jun^r U.S. Navy, the Magnetic apparatus of Hansteen which is in your possession’.Footnote ⁶³ Yet Henry had already copied Hansteen's magnetic cylinder in the early 1830s, and later forwarded the copy to his friend, Alexander Dallas Bache, who in 1838 established the first US magnetic observatory at Girard College (Philadelphia), directly inspired by the British magnetic crusade of the same time. In spring 1834, Bache had measured relative horizontal intensities of terrestrial magnetism at several US sites, using three needles ‘of the form originally adopted by Professor Hansteen’, the one made by Henry and two others made at West Point.Footnote ⁶⁴ Finally, when both Henry and Bache visited Europe (1837–1838), Bache made magnetic measurements at twenty-one stations throughout Europe using ‘a cylinder of the Hansteen model’, thus connecting the US stations to the same standards and stations as in Europe.Footnote ⁶⁵

Another Hansteen magnetometer was destined for South America. While in London in 1826, Erichsen gave his own apparatus to Captain Philip Parker King, who was about to embark on his expedition with HMS Adventure, which accompanied HMS Beagle on its first voyage to the South American coast. For the Hydrographic Office they were conducting maritime surveys of the dangerous waters around the Strait of Magellan, an area of great interest to Hansteen because of its proximity to one of the south magnetic poles. Through letters from South America, King provided Hansteen with valuable observations from London to Maldonado and further through the Strait of Magellan to Valparaiso.Footnote ⁶⁶ Hansteen's apparatus and cylinder were later passed to King's successor in the survey, Captain Robert FitzRoy, who upon HMS Beagle's second voyage of 1831–1836 – with Charles Darwin on board – continued making magnetic observations with Hansteen's cylinder: ‘The apparatus in which it was vibrated, both in Captain King's and Captain Fitz-Roy's voyages, was the well-known one of M. Hansteen’.Footnote ⁶⁷

Sabine became Hansteen's major British supporter from 1825, and he organized a complicated circulation of Hansteen's various magnetometers and magnetic cylinders from 1826. However, still an Army officer, he and his company were sent to Limerick, Ireland, in 1830 and his work on magnetism was temporarily interrupted. Meanwhile, between 1828 and 1830, Hansteen was busy travelling Siberia searching for a magnetic pole, and their correspondence was discontinued between 1829 and 1834. Yet Hansteen also had strong Scottish supporters, and from the late 1820s Edinburgh became his second bridgehead to Britain.

The magnetic survey of Scotland

Hansteen and his magnetometers were introduced gradually in Scotland. First, in 1819, Hansteen's four-pole theory was introduced by Brewster and Carlyle, and Hansteen's magnetometer was described in Rümker's letter in the Edinburgh Philosophical Journal in 1821. Second, in July 1823, Örsted brought an apparatus to the Scottish metropolis and made observations at Brewster's house (10 Coates Crescent). Third, in February 1827, Captain Basil Hall made observations for Sabine with an apparatus from Hansteen in the back garden of his house (8 St Colme Street). By this time, however, Brewster had made a separate move to acquire one of Hansteen's magnetometers. In a letter in November 1826, he proposed,

During summer 1827, Hansteen sent Brewster a magnetometer with his ‘Flat needle’ and Cylinder No 1, which had earlier accompanied Erichsen to Breslau (1824) and Meilænder and Palludan to Hammerfest (1825). Unlike the two boxes and four needles sent to Sabine in 1826 and widely circulated and exchanged on various voyages and journeys, this apparatus stayed in Scotland, eventually inaugurating Britain's first systematic magnetic land survey.

Hansteen's magnetometer remained in Edinburgh for two years until Brewster forwarded it to Sir Thomas MacDougall Brisbane at Makerstoun near Kelso in 1829. A general during the Napoleonic Wars, he was later appointed governor of New South Wales (1821–1825). He was also a science patron, strongly interested in astronomy, navigation and terrestrial magnetism, and in 1808 he established a private observatory at the family estate (Brisbane House near Largs in Ayrshire).Footnote ⁶⁹ While in New South Wales, he established another private observatory at Parramatta employing astronomer Carl Ludwig Rümker and technical assistant James Dunlop.Footnote ⁷⁰ When Brisbane returned to Scotland in 1826, he built his third private observatory at Makerstoun, and he eventually built a fourth magnetic observatory on his estate in 1841. From 1832 to 1860 Brisbane was president of Edinburgh's Royal Society.

Brisbane also helped organize Scotland's first magnetic survey in the late 1820s. During summer 1829, his technical assistant, James Dunlop, took Hansteen's magnetometer and the two needles on a Scottish countryside tour, first along the east coast to Thurso and Tounge up north, then south to Brisbane and Ayr, before returning to Makerstoun. Results were published in the Transactions of the Royal Society of Edinburgh (1834), and according to Dunlop, it was ‘the most extensive series of any which have yet been made in Britain’. Observations were done ‘with Professor Hansteen's method of observing, described in his letter to Dr Brewster, which accompanied the apparatus’, and Cylinder No 1 was checked (June 1827) against ‘Hansteen's standard cylinder from Dollond’.Footnote ⁷¹

Brisbane presented Dunlop's report to Edinburgh's Royal Society in April 1830. The published report in 1834 also included an introductory letter by Brisbane where he emphasized the valuable assistance he had obtained from Hansteen's magnetic chart on his voyage to New South Wales and home determining longitude at sea:

Meanwhile, Dunlop sailed back to the observatory of Parramatta in 1831, and he made additional magnetic observations on his voyage which were submitted to the Philosophical Transactions of the Royal Society of London, but never published.Footnote ⁷³ Nevertheless, a copy of Dunlop's unpublished results was forwarded to Hansteen in March 1832 by James David Forbes, Brewster's protégé and newly elected member of Edinburgh's Royal Society, who on 10 February had observed Hansteen's Cylinder No 1 ‘at the same spot where Mr. Dunlop did so’, at Canaan Cottage near Makerstoun. The slight variation he observed was reported to Hansteen by Forbes's good friend Captain Philip Parker King.Footnote ⁷⁴ Thus, while Sabine was on military service in Ireland, Hansteen had gained another stronghold in Scotland with Brewster, Brisbane, Dunlop and Forbes as main supporters and collaborators.

The BAAS and terrestrial magnetism

In summer 1830, Hansteen returned to Christiania from his great Siberian expedition, during which he communicated some results in letters to Sabine in Limerick. The preliminary results – together with Hansteen's global chart of magnetic intensity – were published in Schumacher's Astronomische Nachrichten (1831).Footnote ⁷⁵ Meanwhile, on 1 June 1831, the magnetic pole near Baffin Bay was conquered by James Clarke Ross, the nephew of John Ross. Without doubt, terrestrial magnetism and polar explorations were hot topics in Britain in 1831.

The British Association for the Advancement of Science (BAAS) was established in September 1831 in York at the Yorkshire Philosophical Society's invitation.Footnote ⁷⁶ The first proposal came from Edinburgh, in a letter from Brewster to Babbage in February 1830 and Brewster presided at the first meeting. Brisbane, too, eagerly supported the initiative, and he eventually presided over the 1834 Meeting in Edinburgh. The study of terrestrial magnetism was an essential feature of these earliest BAAS meetings. In the recommendations from the 1831 Meeting in York – from the committee on mathematical and physical science, including Brewster, Brisbane, Forbes and Scoresby – the highest priority was given to continuing the work initiated by Hansteen and continued by Dunlop: ‘It appears to the Committee highly desirable that a series of observations upon the Intensity of Terrestrial Magnetism in various parts of England be made by some competent individual, similar to those which have recently been carried on in Scotland by Mr. Dunlop.’Footnote ⁷⁷

In the early 1830s, few British men of science had the practical skills necessary to make precise measurements of magnetic intensity. In April 1831, Dunlop had returned to New South Wales as superintendent of the observatory at Parramatta, and, with Sabine on military duty in Limerick, the BAAS turned to whaler and Arctic traveller William Scoresby to continue Dunlop's work, but even he was unavailable. Instead, Scoresby suggested Thomas Stewart Traill, who had accompanied Örsted in Liverpool in 1823 with another Hansteen apparatus. Traill received the magnetometer used by Dunlop, and his results from Liverpool and Manchester were communicated to the 1832 Meeting at Oxford by Scoresby.Footnote ⁷⁸ Hansteen's magnetometer was then passed to Forbes upon his own request, and during summer 1832 he took the portable magnetometer on his central Alps journey to make experiments concerning the effect of heights. Results were presented to Edinburgh's Royal Society in December 1836 and eventually published in 1840 with a map of the central Alps showing the lines of equal horizontal magnetic intensity: ‘Hansteen's instrument was the constant companion of my pedestrian excursions, and had it been in any other form, the present observations would probably never have been made’.Footnote ⁷⁹ By the mid-1830s, many leading proponents of the magnetic lobby had already become accustomed to Hansteen's modes of observation, calculation and standardization, which enabled a collective, systematic approach to studying terrestrial magnetism.

The BAAS quickly became the breeding ground for what eventually emerged as the magnetic crusade, the campaign that Sabine came to lead within the British Association and the Royal Society.Footnote ⁸⁰ In the early years, however, the BAAS was far more concerned with national surveys of magnetic intensity in Britain than with Antarctic expeditions or the establishing a network of permanent magnetic observatories throughout the British Empire. In this initial 1834–1835 campaign, described by Cawood as ‘a false start’ or ‘a premature attempt’, Hansteen's small and portable magnetometers were paradigmatic for observing magnetic intensity when touring the British countryside.Footnote ⁸¹

Towards the 1835 Meeting in Dublin, Sabine in Limerick began collaborating with Lloyd in Dublin on the first magnetic survey of Ireland. They were soon joined by newly returned polar hero James Clark Ross, and at the BAAS Meeting in 1835 Sabine in his address strongly supported Hansteen's four-pole theory and his approach to studying Earth magnetism.Footnote ⁸² Also, the instruments employed for observations of horizontal intensity in surveying Ireland ‘were constructed after the model of that of Professor Hansteen’.Footnote ⁸³ Likewise, during the new magnetic survey of Scotland conducted by Sabine in 1836, observations of horizontal intensity ‘were made in the well-known apparatus of M. Hansteen’.Footnote ⁸⁴ Even when completing the magnetic survey of the British Isles in 1838, Hansteen's method of vibration was still used: ‘Captain Ross's determinations were made with a cylinder (X) vibrated in an apparatus on the well-known plan of M. Hansteen’.Footnote ⁸⁵ Consequently, the BAAS's publication of the respective magnetic charts over Ireland (1836), Scotland (1837) and the British Isles (1839) may be regarded as an outcome of Hansteen's magnetic campaign based on national surveys and using portable magnetometers.

Yet the initiative within the BAAS from Sabine and the Edinburgh savants was gradually taken over by the mid-1830s by academic mathematicians and physicists. At the 1833 Meeting at Cambridge, a standing committee on terrestrial magnetism had been appointed, including Samuel Hunter Christie, James David Forbes and Humphrey Lloyd. Eventually, the British magnetic lobby turned away from Hansteen and his portable magnetometers and towards Humboldt and Gauss, with their network of fixed observatories. Such a system of corresponding magnetic observatories had been established in 1829 by Arago in France, Humboldt in Prussia and Kupffer in Russia, and was soon extended and institutionalized by Gauss and Weber in the Göttingen magnetische Verein founded in 1834. Thus both the study of terrestrial magnetism in general and the magnetic crusade more specifically have previously been described in terms of Humboldtian science.Footnote ⁸⁶

However, Hansteen's magnetometer and its prominence among the leading proponents of the magnetic crusade add another level to this analysis emphasizing the standardization and calibration of instruments and techniques as a precondition for international cooperation. Surely, all measurements with Hansteen's magnetometers and needles were ‘relative’ in comparison to the Dollond cylinder, but as the magnetization of the needle according to Hansteen did not change, the standardized measurements provided a high degree of precision. The subsequent Gaussian method of ‘absolute’ measurement was clearly superior, based on systematic calibration of precision instruments of unprecedented sensitivity, determining exactly the magnetic force of the needle, and expressing its value in absolutes units. Yet before increased precision there was standardization, and this process of technical standardization required a predefined set of competent practitioners or peers capable of reaching agreement on what should count as standard instruments and techniques. Thus, prior to both Humboldt and Gauss, the circulation of Hansteen's magnetometer set the scene for further international collaboration studying terrestrial magnetism.

Furthermore, Hansteen also influenced Humboldt. As mentioned, Humboldt had been introduced to Hansteen's book and atlas while in Paris in 1819. A decade later, before departing for his 1829 Russian expedition, Humboldt spoke at Berlin's Royal Academy of Science on 2 April on the status of terrestrial magnetism research, referring to both Hansteen's Magnetismus der Erde (1819) and his ongoing North Asian expedition.Footnote ⁸⁷ His talk was published in Annalen der Physik with Humboldt's measurements of magnetic inclination and intensity from his earlier South American voyage, previously unpublished, according to the editor, apart from extracts reproduced ten years earlier in Hansteen's Magnetismus der Erde.Footnote ⁸⁸

Before Humboldt's departure for Russia, he had acquired all relevant scientific instruments, including Hansteen's magnetometer. Apparently, Humboldt was aware of Sabine's 1828 publication in the Philosophical Transactions introducing Hansteen's magnetometer, and on 20 January 1829 he wrote to Schumacher in Altona asking him to provide an oscillation apparatus like the one Sabine and Hansteen had. Desperate about possible delays, Humboldt also organized acquisition of another Hansteen magnetometer from the astronomer Peter Andreas Hansen in Gotha, and upon arriving in St Petersburg he had two such instruments, one of which was eventually given to his colleague from Kazan and St Petersburg, Adolph Kupffer. Both Humboldt and Kupffer measured magnetic intensity with Hansteen's magnetometer in Russia during 1829.Footnote ⁸⁹ Also, in Humboldt's famous letter to the Duke of Sussex (1836), where he suggested the British should establish a network of permanent magnetic observatories inspired by Humboldt and Gauss and their Magnetischer Verein, Humboldt paid due respect to Hansteen's Russian expedition, which had explored ‘throughout the immense extent of Northern Asia, the isoclinal, isogonal, and isodynamic curves’.Footnote ⁹⁰

Describing Hansteen's contribution simply as Humboldtian science underscores the impact and acknowledgement Hansteen actually had in Britain during the 1830s. In retrospect, the role of both Humboldt and Gauss in the origin of the magnetic crusade has clearly been exaggerated at Hansteen's expense. From 1819, the circulation of Hansteen's magnetometers throughout his extensive network of collaborators and observers – hugely expanded after 1826 through the efforts of Sabine in London and Brewster in Edinburgh – constituted a significant improvement over previous practice and established a wide network of comparable observations. A decade before Humboldt's famous 1836 letter to the president of the Royal Society, and long before the magnetic crusade was launched in 1839, Hansteen had established a system for international cooperation in studying terrestrial magnetism based on observations with his portable magnetometer and standardized by comparison with his Dollond cylinder in Christiania.