GLOBAL MAGNETIC COLLECTING
Throughout the eighteenth century the British traveled the globe primarily in the interest of their colonies. First and foremost they sought to build and sustain the British Empire through naval and commercial might. In addition, world exploration allowed increased opportunities for enhancing royal and national prestige, expanding geographic knowledge, and collecting a wide range of scientific information. During the second half of the eighteenth century a broad-based "quantifying spirit" took root in Europe. Investigators in Britain and elsewhere enthusiastically assigned numbers to all types of natural phenomena and human activities. At the turn of the century, quantification and measurement affected such diverse areas as experimental physics, meteorology, geodesy, chemistry, forestry, and political economy. Exemplifying the desire to quantify, British naval explorations of the late eighteenth century gathered, measured, and classified data of all kinds— astronomical, ethnological, meteorological, geographical, and natural historical.
In addition, this "quantifying spirit" or impulse to measure accompanied an urge to build better more precise instruments including magnetic instruments. Although few natural philosophers and instrument makers actually collected terrestrial magnetic data, many saw fit to design, construct, and test magnetic instruments— azimuth compasses, dipping needles, variation compasses, etc. Ultimately, most instrument designers and builders depended on navigators to provide them with global magnetic data. As they had since the sixteenth century, eighteenth-century mariners measured magnetic variation or declination to correct their courses. Ships' logbooks and journals routinely recorded variation along with latitude, longitude, temperature, wind, and weather conditions. The less frequently recorded magnetic dip had little practical utility. As such, variation dominated the magnetic data collected during the eighteenth century. A third magnetic component, magnetic intensity was not measured until the late eighteenth century in France and the early nineteenth century in Britain. Counting the vibrations or oscillations of a suspended magnetic needle within a given amount of time determined relative magnetic force or intensity at different geographic locations. Intensity, however, did not became important to British collecting efforts until the 1820s.
Regardless of continuing interest in magnetism during the eighteenth century, the nineteenth century witnessed a marked acceleration in the study of magnetism and terrestrial magnetism. The Philosophical Transactions of the Royal Society of London clearly illustrated the growing interest in the study of magnetism and geomagnetism after 1820. Between 1781 and 1820 there were only a dozen papers published dealing with magnetic topics, yet from 1821 to 1830 there are nearly forty papers related to magnets and magnetism. Several early nineteenth-century developments contributed to this reawakened activity. First, the recognition of ship magnetism led to a variety of considerations regarding navigation by compass and the collection of magnetic data. Second, the renewed search for the North-west passage after the Napoleonic wars gave impetus to the search for the north magnetic pole. It also led Arctic explorers to higher and higher latitudes where they observed the curious behavior of the compass. Third, the possible connections between magnetism and other forces of nature gave great impetus to the experimental study of magnetic effects, particularly after the discovery of electromagnetism in 1820. Though clearly reflected in navigational writings, this last development pertained primarily to experimental physics which will be treated in the final chapter.
Although eighteenth-century British voyages gathered magnetic measurements, the study of magnetism generally received less attention than other areas. This general trend held true into the early nineteenth century. Within the context of global exploration and scientific collecting, this chapter examines the changing motives for gathering magnetic data. Particularly, it discusses the shifting reasons for measuring terrestrial magnetic phenomena from 1750 to 1835. The respective roles of navigators, natural philosophers, and instrument makers are also examined. As a rule, navigators gathered terrestrial magnetic data, instrument makers designed and constructed instruments, and natural philosophers analyzed and interpreted the amassed data. With few exceptions, this pattern held for most of the period.
Magnetic Collecting and Eighteenth-Century Voyages
Since the sixteenth century, navigators had recorded magnetic variation for correcting the course of their ships. Though this practice continued, the effort to measure variation and other scientific data gradually intensified in the eighteenth century. Changing motives and methods of collecting magnetic data become clear when the voyages of the late eighteenth century are examined, particularly those of Captain James Cook and Captain Constantine John Phipps. Cook, Phipps, and others carried with them the best available scientific instruments including magnetic apparatus. As well, trained astronomers accompanied many of these voyages. Both navigators and their astronomers had more scientific training than earlier navigators. Magnetism, nevertheless, gained less attention than other areas. Though the quest to determine longitude by magnetic means persisted, it had all but disappeared at the turn of the century.
Few eighteenth-century natural philosophers pursued Halley's plan of determining longitude by the periodic updating of variation charts. With little support, Newton's successor at Cambridge, William Whiston, sought to use maps of magnetic dip for determining both longitude and latitude. Throughout the century, longitude schemes akin to Halley's and Whiston's failed to gain any large following. In the 1740s, Fellows of the Royal Society, William Mountaine and James Dodson, advertised requests for magnetic data which met with little interest. Wishing to update and extend the scope of Halley's charts, they explained their motives in 1755:
The advantage that will arise by extending the variation lines over the land, as well as sea, will be the confirmation of those drawn over the waters; the continuation of which, from sea to sea, will be thereby conspicuous, and we shall be enabled to judge better of their nature, properties and causes; and, if the same can be extended over all the parts of the known world, the eye will be presented, at one view, with the different degrees of attraction, with which all the parts of this great magnet are endued, at the time when such lines are drawn.
Seeking to benefit trade, navigation, and natural knowledge, Mountaine and Dodson presented a set of tables to the Royal Society of London in 1757. Compiled from approximately 50,000 observations in the log books and journals of the Royal Navy, the East India Company, the Hudson's Bay Company, and several individuals, these tables illustrated the distribution of magnetic variation for the years 1710, 1720, 1730, 1744, and 1756. In contrast to their stated goals, however, only the measurements of Royal Observatory astronomer, James Bradley, were land-based. Until the nineteenth century, extensive land-based magnetic observations remained a rarity in Britain.
While complaining of limited and deficient information, Mountaine and Dodson limited their efforts to compiling data "without attempting to introduce any hypothesis." They supposed that periodic compilations of magnetic data might allow future philosophers to discover the rules of secular and diurnal variation. Though venturing no hypothesis for these rules, Mountaine and Dodson supposed earthly magnetism "influenced by various and different magnetic attractions, in all probability occasioned by the heterogeneous compositions in the great magnet, the Earth." Hence, they, like most others at mid-century, accepted the Gilbertian notion of giant terrestrial magnet.
Despite Mountaine and Dodson's more purely scientific objectives, the primary reason for understanding magnetic changes for them and others in the eighteenth century remained the improvement of navigational science. Practical application drove the majority of those interested in updating magnetic charts. For instance, in 1763, a ship's surgeon David Ross sent variation measurements to Mountaine and noted them "of great service to philosophy in general, but particularly to navigation, as in future ages they may serve as a basis, to found its theory upon." In 1776, Mountaine sent a set of earlier observations to Astronomer Royal Nevil Maskelyne. He reiterated his motivations to Maskelyne:
the discovery of that law [of secular variation] must greatly depend upon such comparisons made from multitudes of good observations taken at different periods, and those over the whole face of the terraqueous globe; but until that law is certainly known, charts can be constructed only from time to time from the latest observations.
More than half a century later, Mountaine's vision for the regular global collection of magnetic data began to take shape. By then, the motives behind such massive efforts had shifted with navigational application taking subsidiary importance.
In contrast to Halley's efforts, most eighteenth-century natural philosophers left the measurement of terrestrial magnetic phenomena to experienced mariners. Natural philosophers and instrument makers stuck to the tasks of designing, constructing, and testing magnetic instruments. For instance, in the 1760s, the magnetic experimenter, Gowin Knight, designed an improved azimuth compass which stood until the early nineteenth century as the standard for Navy use. Similarly, London instrument maker Edward Nairne designed the standard dipping needle. Nairne determined the dip for London in 1772, yet did not use his instrument on a regular basis. Historian Patricia Fara characterized the division as an "unequal distribution of magnetic knowledge" between maritime practitioners, who desired sea-based practical navigational techniques and natural philosophers, who sought land-based theoretical knowledge of magnetism. Though the practical and theoretical interests of mariners and natural philosophers overlapped, the participants tended to stress one aspect or the other in their work.
During the last quarter of the eighteenth century, instrument makers and natural philosophers continued designing magnetic instruments for navigational use. In 1776, Henry Cavendish tested Nairne's dipping needle and several meteorological instruments at the Royal Society. Though the Royal Society kept a meteorological journal with tables of magnetic variation and dip, such data, unlike temperature or atmospheric pressure, were not collected on a regular monthly basis. Cavendish's concerns lay in testing the instrument's accuracy and describing possible sources of error, not in prolonged, systematic geomagnetic observation. Comparing indoor and outdoor readings of dip, he determined that errors arose from ironwork in the apartments of the Royal Society. Describing additional sources of error, he concluded that Nairne's dipping needle was at least as exact, if not more so, than any previous instrument. He also described a method for observing dip in which the instrument was rotated 180°, the observations repeated, and then the poles of the needle were reversed, and observations again repeated. Deferring to Cavendish as an authority, navigators often used this technique to determine the "true dip."
While natural philosophers and instrument makers designed and tested instruments, officers in the British Royal Navy put them to use around the globe. A series of naval expeditions in the 1760s and 1770s allowed for observation and measurement on a grand scale. In spite of the increasingly scientific tone of these voyages, promoting British sea power, commerce, national pride, and geographic knowledge remained the traditional objectives. Illustrating these concerns in 1764, Commodore John Byron's official instructions for a voyage to the Pacific noted:
Whereas nothing can redound more to the honour of this nation, as a maritime power, to the dignity of the Crown of Great Britain, and to the advancement of the trade and navigation thereof; and whereas there is reason to believe that lands and islands of great extent, hitherto unvisited by any European power, may be found in . . . within latitudes convenient for navigation, and in climates adapted to the produce of commodities useful in commerce . . . his Majesty . . . has thought fit that it [a voyage] should now be undertaken.
For a young King George III, expanding British dominion and exploring unknown portions of the globe, particularly the vast Pacific Ocean, remained of great importance.
Geographical motives, among others, overshadowed the collection of magnetic data during eighteenth-century explorations. Geography, astronomy, longitude, and natural history garnered the lion's share of attention. Following the example of James Cook, Royal Navy officers frequently had the necessary skills for careful observing or learned them on the job. Indeed, Cook's predecessors had lacked the mathematical and astronomical training and the technical skills which he and later naval officers often possessed. In 1768, Cook received detailed instructions from the Board of Longitude drawn up by Astronomer Royal, Nevil Maskelyne. Not surprisingly, astronomical items related to longitude determination such as lunar observations and the eclipses of Jupiter's satellites dominated the list. Taking lower priority were magnetic measurements, appearing twelfth out of fifteen items in Maskelyne's instructions.
Most of the essential data directly related to the determination of longitude. To assist the officers in these tasks, the Board of Longitude appointed astronomers to collect and measure astronomical data. Regarding the numerous lunar observations of appointed astronomer Charles Green, Cook commented:
[Mr. Green] was Indefatigable in making and calculating these observations . . . by his Instructions several of the Petty officers can make and Calculate these observations almost as well as himself: it is only by such means that this method of finding Longitude at Sea can be put into universal practice.
On Cook's first Pacific voyage (1768-1771) and most others of the late eighteenth century the accurate determination of longitude remained the primary navigational concern.
Earlier in the century, the quest for longitude had been stimulated when Parliament passed the Longitude Act of 1714. This legislation not only established the Board of Longitude, but also offered enormous monetary rewards for a reliable method of finding longitude— £10,000 within sixty miles, £15,000 within forty miles, and £20,000 within thirty miles. Throughout the eighteenth century, finding accurate methods of determining longitude retained a singular significance, particularly for a maritime nation such as Britain.
In addition to the quest for longitude, observing the transit of Venus held enormous scientific importance for Cook's initial voyage. Indicative of the transit's importance, orders for its observation on the South Pacific island of Tahiti appeared first in Cook's official instructions from the Admiralty. After disappointing observations of the transit of 1761, astronomers hoped that observing the transit of 1769 (the last opportunity to observe such an event for over a century) from different positions would allow an accurate determination of the distance between the earth and sun. Cook and Green, upon returning to England in 1771, reported transit observations in great detail to the Royal Society of London. Though their reports also included tables of magnetic dip and variation, astronomy clearly held the greater importance.
Under the aegis of the Board of Longitude, Maskelyne's instructions for Cook's second Pacific voyage (1772-75) followed a similar pattern. Longitude and astronomical observations again dominated the list. As a perennial navigational problem, the determination of longitude saw the emergence of two practicable solutions in the late eighteenth century. The method of lunar distances, refined and advocated by Nevil Maskelyne, used the moon's motion against a background of stars as a time keeping device. This method depended upon numerous observations and corrections, intricate mathematical calculations, and accurate lunar tables. A simpler method relied on the development of an accurate marine chronometer. By the early nineteenth century chronometers were commonly used for determining longitude. The method, in principle, was simple since it required comparing local time with Greenwich time kept by the chronometer. Each hour difference in time represented 15° difference in longitude as measured east or west from Greenwich. Replacing more complex and inaccurate methods, determining longitude by chronometer made possible safer, easier navigation. In fact, by the 1820s chronometers became widely available and Parliament abolished the Board of Longitude in 1828.
Illustrating longitude's importance in the eighteenth century, Maskelyne first ordered Cook's appointed astronomers, William Wales (1734-1798) and William Bayly, to thoroughly test a copy of the chronometer designed by carpenter turned clockmaker, John Harrison. In addition, Maskelyne's instructions included numerous meteorological and astronomical observations and pendulum observations for determining the figure of the earth. While the Royal Society and Board of Longitude provided magnetic apparatus made by Nairne, Adams, and other instrument makers, magnetic observations received only one line in the instructions to "observe, or assist at the Observations of the variation of the Compass; and observe the inclination of the Magnetic Dipping needle from time to time." Maskelyne's phrasing again indicated the lesser importance of magnetism.
During all of his journeys, Cook exhibited the spirit of quantification and this spirit's connection to improved instrumentation. In 1773, one of Cook's journal entries made this link apparent:
Such are the improvements Navigation has received from Astronomers of this Age, by the Valuable Table they have communicated to the Publick under the direction of the Board of Longitude contained in the Astronomical Ephemeris and the Tables for correcting the Apparent Distance of the Moon and a Star from the effects of Refraction and Parallax . . . Much Credet [sic] is also due to the Mathematical Instrument makers for the improvements and accuracy with which they make their Instruments, for without good Instruments the Tables would loose [sic] part of their use.
However, though astronomical instrumentation gained great praise, magnetic instruments were frequently condemned. Finding the magnetic variation on a moving ship had never been a simple task. In De Magnete, William Gilbert had remarked, "Even expert navigators find it very difficult to observe the variation at sea on account of the ship's motions and her tossing in every direction, though they may employ the best instruments yet devised and in use." Regardless of attempts to improve azimuth compasses and other magnetic instruments, similar complaints continued in the eighteenth century.
Finding magnetic variation required determining the altitude and bearing of a celestial object, usually the sun. In addition, it involved corrections for atmospheric refraction and quite a bit of mathematical calculation. Exacerbating matters, variation measurements depended on a variety of circumstances including the geographic location, the time of day, the placement of the compass on the ship, the same compass on another ship, and different compasses used on the same ship. Illustrating the difficulties, Cook remarked in 1774:
Sence [sic] we have been a Mongest [sic] these Islands, we have found it difficult to determine the Variation with accuracy. Our Compasses have given from 8° to 12° the same Compass would vary so much on different days and even between the morning and evening of the same day, when the Ship's Change of Situation has been but very little.
The article, "Variation," in the second edition of Encyclopaedia Britannica (1778-83) similarly lamented that because variation observations were "loose and inaccurate," it was impossible to represent them with precision.
As a final difficulty, magnetic variation changed depending on the ship's head or direction of travel. Though the cause of this phenomenon remained a mystery until the early nineteenth century, Cook's second voyage recorded numerous instances of it. Cook, for example, remarked in 1773, "this was not the first time we had made this observation, without being able to account for it." Several months later, his second lieutenant, Charles Clerke, noted:
AM We took several sets of Azimuths by Knight's and Gregory's Compasses. We've often observ'd 3° & sometimes 4° difference in the Angle of the Magnetic Azimuth by shifting the Tacks of the Ship, and taking the observations from the different sides— now this being a fine Morning, smooth Water, and just wind enough to veer her Head whichever way answers best our purpose; the following Obervations were made with two different Compass's [sic] to attain this Difference which I'm totally at a loss to account for.
During Cook's final voyage (1776-80), Wales found that by placing the ship’s head in the opposite direction, the variation differed from 3° to 6°, sometimes as much as 10°. He noted similar discrepancies when traveling up or down the English Channel. Baffled by this phenomenon, navigators and astronomers usually attributed it to imperfect instruments.
Finding the magnetic dip was even more difficult and frustrating than variation. Even on dry land, determining dip with any precision was a time-consuming and troublesome process. Measuring the dip at Hudson's Bay in 1775, Thomas Hutchins remarked, "I took particular care in placing the instrument in the magnetic meridian, and was near four hours before I got it right. The observations employed four hours more." Despite improvements in the design and construction of dipping needles, they too suffered harsh criticisms. Practically impossible to use unless the ship was securely anchored or the instrument was on shore, dipping needles gained a reputation for being difficult to use and unreliable. In 1777, William Wales reported, "the dipping needle . . . we took ashore . . . was so much out of balance, and so difficult to get in [balance] again . . . [that] we did not get it perfectly adjusted before we went away, and of course were not able to get any observations of this kind at this time."
Reiterating the difficulties of using the dipping needle, Wales' former assistant, William Bayly, noted in 1782, "when at sea the needle seldom rested quite steady, but vibrated one or more degrees each way." To minimize these errors he took several precautions. Following Cavendish's technique, Bayly made ten observations with the dipping needle facing east and west alternately, then switched the needle's poles and repeated the observations. Through this commonly used technique, the mean of multiple observations determined the "true dip." Again paralleling Cavendish's work, Bayly removed the instrument as far as possible from iron to reduce errors. Although Wales, Bayly and others recognized the effects of nearby iron on their magnetic instruments, they failed to realize that compass deviations arising from changes of the ship's head also arose from shipboard iron. Investigators continued to fault the instruments. Indicating a general distrust of magnetic instruments, a commentator complained in 1800 that azimuth compasses and dipping needles, despite being the best money could buy were "totally inadequate to the correct and useful purposes of navigation, or indeed to any correctly useful purpose whatever." These misgivings persisted in the nineteenth century.
Regardless of the difficulties of measuring magnetic data, Cook's explorations earned a reputation for their excellent charts, precise astronomical observations, and geographic discoveries. Geographic motives continued to play a major role in several British explorations during the late eighteenth century. Though the notion of a fertile, populous southern continent (i.e., Terra Australis Incognita) generally fell into disrepute following Cook's second voyage, other ideas, also originating with theoretical geographers, lingered throughout the century. Theories espousing the existence of a North-west passage from Atlantic to Pacific and an open polar sea gained many enthusiastic adherents. In the mid-1770s, naturalist-lawyer Daines Barrington (1727-1800) appealed to geographical theories and navigators' stories of ice-free seas to bolster support for a trip to high northern latitudes. Barrington embraced the ideas of Swiss geographer, Samuel Engels (1702-1784) who had argued in 1765 for the existence of an open polar sea (i. e., "une mer vaste et libre"). Prompted by Barrington's enthusiasm, the Royal Society of London proposed to the Admiralty a voyage to the North Pole. As a result, Captain Constantine John Phipps of the Royal Navy set out in April, 1773, "to try how far navigation was practicable towards the North Pole." Though Phipps' voyage primarily sought the extension of geographical knowledge, it also amassed natural historical, astronomical, and navigational data. Paralleling Cook's earlier efforts, the expedition involved cooperation between the Board of Longitude, Admiralty, and Royal Society. As in earlier voyages, Maskelyne ordered appointed astronomer Israel Lyons (1739-1775) "to make nautical & astronomical observations & to perform other Services tending to the improvement of Geography and Navigation." The expedition received an array of instruments designed by prominent instrument makers including, a sextant, telescope, chronometers, pendulum, hygrometer, barometer, manometer, and Nairne's dipping needle. Similar provisioning of instruments continued in Arctic explorations of the nineteenth century.
A wall of impenetrable ice prevented Phipps in His Majesty's Ships (H.M.S.) Racehorse and Carcass from going much beyond Spitsbergen (east of Greenland). Nonetheless, the expedition continued to collect and measure. Phipps, however, complained that if scientific observations had been more than a secondary consideration, they might have been "more numerous and satisfactory." While geography, natural history, and astronomy dominated the observational efforts, Phipps also took an interest in magnetism. Magnetic observations received the "most scrupulous attention" to remove accidental error. Despite numerous precautions, Phipps remarked that his compasses, while adequate for navigating the ship, failed to give a degree of precision fine enough for testing or formulating a theory. The variation, he wrote,
always an interesting object to navigators and philosophers, became peculiarly so in this voyage from the near approach to the Pole. Many of the theories that had been proposed on this subject, were to be brought to the test of observations made in high latitudes, by which alone their fallacy or utility could be discovered. They, of course, engaged much of my attention, and gave me the fullest opportunity of experiencing with regret, the many imperfections of what is called the azimuth compass.
In spite of observing conditions deemed ideal, Phipps could not account for the irregular, often sudden changes in the variation in high latitudes. Like earlier investigators, he blamed the instruments.
Three years after Phipps' failure to reach the North Pole, the Admiralty proposed another voyage with comparable geographic and scientific motives. With encouragement from the Royal Society, the Admiralty ordered Cook in 1776 to find "a Northern Passage by sea from the Pacific to the Atlantic Ocean." Exemplifying the quantifying spirit, the official instructions for Cook's final voyage included an immense list of things to measure and observe:
as far as your time will allow, very carefully to observe the true situation of such places, both in latitude and longitude, the variation of the needle, bearings of headlands, height, direction and course of the tides and currents, depths of soundings . . . and also to survey, make charts, and take views of such bays, harbours and different parts of the coast, and to make such notations thereon as may be useful either to navigation or commerce . . . observe the nature of the soil and the produce thereof, the animals and fowls . . . the fishes . . . metals, minerals, or valuable stones, or any extraneous fossils . . . seeds of such trees, shrubs, plants, fruits and grains . . . [and] observe, the genius, temper, disposition and number of the natives and inhabitants . . .
Aided by Lieutenant James King and astronomer William Bayly, Cook used the best available instruments for recording astronomical, oceanographic, and geophysical data. In their compiled observations published in 1782, the pages devoted to terrestrial magnetism indicated its relative importance. Bayly, Cook, and King included separate accounts related to astronomy (totaling 160 pages), chronometers (40 pages), meteorology (40 pages), magnetic variation (45 pages), and magnetic dip (15 pages). As their accounts also show, variation measurements continued to overshadow those of dip. Variation was easier to measure aboard a moving ship. More importantly, variation had practical navigational utility and dip did not.
In 1778, Cook, like Phipps, encountered impenetrable ice and turned back at the appropriately named Icy Cape on the northwest coast of Alaska. Upon returning to the Sandwich Islands (i.e., Hawaiian Islands), Cook was murdered by islanders in early 1779, ending his illustrious career of exploration and careful observation. As we have seen, during the voyages of Cook and Phipps, three concerns guided the majority of measuring and collecting— geography, longitude, and natural history. Officers like Cook, King, and Phipps, and astronomers like Wales, Bayly, Green, and Lyons (and naturalists including Joseph Banks) gave their closest attention to mapping unknown lands, testing chronometers, calculating the longitude by astronomical methods, and collecting new plants and animals.
When compared with these activities, eighteenth-century investigators did not give high priority to the collection of magnetic measurements. Certainly navigators and astronomers diligently measured variation and dip, but these were given less attention than more important, less frustrating areas. Nevertheless, through careful observations, investigators recognized numerous changes in variation, including those depending on the direction of the ship's head. While often attributed to flawed instruments, the true source of these irregularities remained unknown. Because the instruments were often blamed, compass deviations stimulated a further drive to improve magnetic apparatus.
Cook's voyages set a high standard and a familiar pattern for future explorations of the French and the British. Later British efforts commanded by naval officers stressed the prestige, power, and national honor of geographical objectives. As well, the links between Royal Society, Board of Longitude, and Admiralty continued shaping the scientific goals of later expeditions. Like their predecessors, nineteenth-century explorers received the best available scientific instruments for measuring a wide range of phenomena. Also echoing Cook and Phipps, later expeditions showed an awareness of compass irregularities.
Early nineteenth-century investigators began to recognize that compass deviations originated from quantities of iron in and on the ship. Ship magnetism, also called "local attraction" or "compass deviation," affected the accuracy of all shipboard magnetic measurements. Hence, increasing amounts of iron in combination with increasingly sensitive magnetic instruments led to a wariness of all ship-based measurements. Eventually these developments stimulated strictly land-based magnetic observations performed far from the ship's disturbing influence. The next section examines the recognition of ship magnetism in greater depth and the effects it had upon magnetic collecting.
Iron in the Ships: Matthew Flinders and William Bain
Great Britain had relied on its sea power for several centuries, and investigators had long sought to save money and lives by improving navigation. Despite the solution of the longitude problem in the late eighteenth century, shipwrecks continued to be commonplace in the nineteenth century. Given the dangers of nocturnal navigation, gales, icebergs, storms, strong ocean currents, and human error, many factors possibly contributed to these shipwrecks. In 1804, H. M. S. Apollo and nearly forty other vessels ran aground on the northern coast of Portugal. An estimated three hundred sailors lost their lives from cold, hunger and drowning. Eight years later the H. M. S. Hero ran aground near Texel Island off the Netherlands. Around the same time, the H. M. S. Defiance and St. George wrecked on the western coast of North Jutland (Denmark). On these three ships alone nearly two thousand suffered or died. In 1831, the H. M. S. Thetis set sail from Rio de Janeiro. One day into the journey the ship met her fate:
the first intimation they had of being near land, was the jib-boom striking against a high perpendicular cliff, when the bowsprit broke short off, the shock sending all three masts over the side and thus in a moment perished twenty-five valuable lives, and a fine vessel, with her cargo, worth nearly a quarter of a million sterling.
Incidents of this kind remained commonplace. In fact, even as late as the period from 1852 to 1860, approximately one in every two hundred British ships ran against unseen obstacles or collided with other vessels. During this period, more than seven thousand people lost their lives.
In addition to the many dangers contributing to these shipwrecks, another grew increasingly prominent during the nineteenth century. More iron fittings, iron cannon, iron equipment and, later, all-iron and steel hulls increased the potential for navigational errors. By 1850, iron was the principal building material in ship construction; after 1880, steel overtook iron. Rising amounts ferruginous materials contributed to navigational errors and shipwrecks. This nineteenth-century problem had been largely absent or unnoticed in previous centuries, during an age of primarily wooden ships.
Though Cook, Wales, and others in the late eighteenth century noted deviations in variation arising from changes in the ship's direction or head, they attributed these alterations to imperfect instruments. While navigators since at least the sixteenth century realized that the close proximity of iron affected the compass, they failed recognize how this influence exerted itself. Neither did they understand the interactions between terrestrial magnetic forces and those exerted by iron masses surrounding the compass. Most assumed the simple attractive power of the north end of the needle towards iron (hence the term "local attraction"). For instance, in 1794, Captain Murdo Downie remarked, "I am convinced that the quantity and vicinity of iron in most ships have an effect in attracting the needle; for it is found by experience that the needle will not always point in the same direction when placed at different parts of the ship." Though Downie and others recorded iron's disturbing effects, they failed to link compass deviations arising from changes in the ship's head with the presence of shipboard iron. The research of Matthew Flinders, William Bain, and others in the early nineteenth century slowly altered the understanding of this phenomenon.
While held by French authorities on the Ile de France (Mauritius) in 1804, Captain Matthew Flinders (1774-1814) wrote a letter to Sir Joseph Banks, the President of the Royal Society. In this letter he reported several magnetic observations made during a survey of the southern coast of New Holland (Australia) in 1801-02. As in earlier voyages, accurate mapping had stood as the primary goal of Flinders' expedition in H.M.S. Investigator. Mirroring previous efforts, the Admiralty instructed Flinders to measure numerous data including winds, tides, currents, latitude, longitude, and magnetic variation. Flinders and his appointed astronomer, John Crosley, brought with them a wide assortment of instruments, including chronometers provided by the Board of Longitude.
In his letter to Banks, Flinders reported observed changes in magnetic variation with alterations of the ship's head. While performing his surveying of the Australian coast, Flinders carefully took magnetic bearings of objects at sea and land. The consistent discrepancies of these measurements suggested shipboard iron as the possible cause. Of Wales' earlier efforts, Flinders later reflected, "it seems indeed extraordinary, that with the attention paid by Mr. Wales to [compass deviations], he should not have discovered, or suspected, that the attraction of the iron in the ship was the primary and general cause of the differences so frequently observed." Echoing the complaints of his predecessors, Flinders noted:
That the compasses, even in the Royal Navy and to this day, are the worst constructed instruments of any carried to sea, and often kept in a way to deteriorate, rather than to improve their magnetism, cannot be denied; but errors arising from the badness of compasses would not be reducible to regular laws as those were in the Investigator . . .
Testing his idea that shipboard iron was the culprit, Flinders took magnetic bearings of a distant object with the ship's head pointed in different directions, and identical readings on shore with a theodolite. His careful comparisons of ship-based and land-based observations resulted in several general conclusions. First, Flinders recognized that the maximum deviations occurred with the ship's head pointed nearly east or west. Second, minimum deviations differences happened with the ship pointed nearly north or south, i.e., aligned with the magnetic meridian. Finally, differences in variation between the cardinal points of the compass took on intermediate values between minimum and maximum errors.
Additional observations suggested that compass deviations also depended upon the local dip. With various factors in mind, Flinders put forth an empirical generalization later known as Flinders' Rule. This rule stated, "the error produced at any direction of the ship's head, would be to the error at East or West, at the same dip; as the sine of the angle between the ship's head and the magnetic meridian, was to the sine of eight points, or radius." Hence, changes in variation depended upon the direction of the ship and the amount of dip as well. Such a realization eventually lent new practical utility to dip measurements. Further complicating matters, Flinders found that the ship's distance from the line of no magnetic variation affected the amount of deviation.
Regarding the influence of shipboard iron, Flinders reported to Banks three general conclusions. First, the attractive power of different ferruginous bodies on the ship collected into something analogous to focal point or center of gravity. This center of magnetic attraction usually coincided with the location of the greatest quantity of iron on the ship. Second, the magnetic focal point had the same kind of attraction as the terrestrial magnetic pole of the hemisphere where the ship was located, the southern hemisphere in Flinders' case. As a result, compass deviations would be reversed in opposite hemispheres (i.e., north and south). Third, in ships of war, the attractive power of the focal point interfered with a compass placed in the binnacle. This last conclusion required procedures aimed at correcting or preventing navigational errors.
Flinders demonstrated a link between changes in the ship's head, iron in the ship, and terrestrial magnetic phenomena. In a way his predecessors had not, he explicitly connected compass deviations, shipboard iron, and dip. His conclusions brought with them a practical reason for observing magnetic dip as well as new procedures for collecting magnetic data. Because eighteenth-century magnetic charts and tables had been compiled without a knowledge of local attraction's effects, earlier magnetic measurements could not be considered reliable.
Generally refraining from theoretical discussion, Flinders viewed himself as a collector not an interpreter of terrestrial magnetic data. He did not consider himself qualified to comment on theoretical issues. Cautioning that "constant employment upon practice" had not allowed him, "to become much acquainted with theories," Flinders wrote to Banks:
I shall leave it to the learned on the subject of magnetism to compare the observations here given with those made by other in different parts of the earth, and to form from them an hypothesis that may embrace the whole of the phenomena: the opinion I have ventured to offer is merely the vague conjecture of one who does not profess to understand the subject.
Regarding local attraction of land masses, he similarly noted in 1814:
In some parts of this little discussion upon the attraction of land, I feel to have stepped out of my sphere; but if the hints thrown out should aid the philosopher in developing a system of magnetism applicable to the whole earth, or even be the means of stimulating inquiry, the digression will not have been useless.
In these humble remarks Flinders illustrated a persistent division between navigators and natural philosophers. Though interested in aiding natural philosophers, his approach remained essentially practical and non-theoretical.
Towards the end of Flinders' internment on the Ile de France, he proposed future plans for
making all the necessary experiments for ascertaining the magnetism of ships as far as can be useful to the accuracy of navigation; as also of making such as may enable me to determine the points on the surface of the Earth to which the needle of the compass is directed, and also the places of the poles within the earth which affect the dipping needle; what I have done here being only preparatory . . .
After six and a half years of imprisonment by the French, Flinders returned to England and, in 1810, appealed to the Admiralty for a continuation of his experiments. In 1812, a series of observations made on five ships at Sheerness and Portsmouth confirmed that iron caused deviations in the way Flinders described. Nevertheless, many mariners continued to reject his explanation. Experienced seamen recognized compass deviations but, as Flinders pointed out, "the most general result of their observations seems to have been an opinion, that within some undefined and variable limits this instrument was radically imperfect." After Flinders' death, similar judgments prevailed among many mariners.
Like Flinders, William Bain, a Master in the Royal Navy, hoped to convince navigators that shipboard iron contributed to their navigational woes. In 1817, Bain proclaimed that the subject was a "fact of much importance to navigation, and consequently to the general interests of the British nation." He sought to direct nautical men to compass deviations arising from ship magnetism. Ignorance of local attraction, he argued, had occasioned many terrible losses and fatal accidents.
Bain pointed out that experiences during the Napoleonic wars had taught many navigators that setting a course opposite from that initially steered could lead to navigational misfortune. Given the ignorance of merchants, "neither skill, experience, nor fortitude" could guard against such errors. He argued that local attraction had contributed to a multitude of accidents in the English Channel, the St. Lawrence River, and elsewhere. Pointing to ship magnetism as the culprit, Bain reiterated the difficulties of convincing navigators otherwise. Unfortunately, most held fast to the notion that flawed instruments or unnoticed ocean currents were to blame. Bain's work, like Flinders', illustrated a division between navigators and natural philosophers. He supposed that the uncertainties and doubts accompanying compass deviation could be removed by employing a few scientific men. Trained men of science, hired by the government, could immensely improve navigational science. Hence, Bain looked to scientists rather than navigators to solve the problem.
Again paralleling Flinders, Bain took an empirical and non-theoretical approach to his study of local attraction. He noted that "one single fact established by experience, is stronger and deserving of more credit than all the hypotheses founded on theory that can be brought together." After slightly modifying Flinders' Rule, Bain offered several precautions for guarding against local attraction. First, the binnacle should be permanently fixed with copper, rather than iron, bolts and nails. Second, variation measurements with the azimuth compass should always be performed on the binnacle to ensure uniformity. Third, all ships of war and merchant ships loaded with cargo should, before setting sail, choose a distant fixed object and compare its magnetic bearings on and off ship with the azimuth compass. This procedure involved swinging the ship’s head east and then west to determine maximum compass deviations. For future reference, these deviations should be recorded in the ship’s log. These precautions, argued Bain, would help reduce navigational errors arising from ship magnetism.
As we have seen, both Flinders and Bain sought to remedy the widespread ignorance of local attraction which persisted in the navigational community. Their main hope was to diminish the loss of lives and property attributable to compass deviations. To this end, both men determined empirical rules and practical techniques for calculating navigational errors arising from local attraction. Beyond a few general assumptions regarding terrestrial magnetism, their work remained empirical and lacked theoretical content. Regarding theoretical approaches to magnetism, both men deferred to the judgments of scientifically-trained men.
From the 1820s onward, interest in local attraction expanded because more iron (and later steel) was used in ship construction, more sensitive instruments were developed, and compass deviations became more of a hindrance. Throughout the nineteenth century, increasing amounts of iron were used for ballast, water tanks, cables, gun carriages, capstans, masts and other parts of ships. Not surprisingly, the British government and private shipping firms took great interest in alleviating navigational and surveying errors caused by iron in the ships. The most common methods of correcting these deviations involved carefully recording the compass deviations before the ship left port; comparing the readings of a compass located above deck with those of the steering compass; or the application of various compensation devices, including iron plates, iron bars, and magnets situated near the compass so as to counteract or determine the effects of local attraction. In-depth discussion of these methods has been examined in the existing scholarship.
Beyond the intense interest in navigational error, the recognition of local attraction also fostered general interest in terrestrial magnetic phenomena. Attracted to a practical problem with important implications for both accurate navigation and map making, greater numbers of scientifically-trained men showed interest in the study of magnetism. In addition to local attraction, the renewed search for the North-west passage in 1818 fostered increased interest in terrestrial magnetism. Most theoretical estimates placed the north magnetic pole in the Arctic, yet there was little agreement on its precise location or its possible movements. Hence, Arctic exploration allowed the compilation in high latitudes of magnetic measurements against which theories could be tested or new explanations devised.
Therefore, arising from the recognition of local attraction and the renewal of Arctic exploration, magnetic collecting gained greater attention in the late 1810s, than it had in the previous century. Admittedly, both practical and scientific goals coexisted in the eighteenth and nineteenth centuries. Nevertheless, a greater scientific understanding of terrestrial magnetism became increasingly important in nineteenth-century efforts. In any case, the reasons for collecting magnetic data altered in both degree and kind from one century to the next. In the eighteenth century, relatively few natural philosophers stressed global magnetic measurements and those who did were driven by navigational purposes. By the 1820s, however, increasing numbers of scientifically-trained men showed interest in amassing, arranging, and interpreting terrestrial magnetic phenomena for non-navigational reasons. We will return to their work in the final chapter.
Napoleonic Interlude and the Revival of Arctic Exploration
The Napoleonic wars diverted the Royal Navy from exploration, resulting in decreased opportunities to classify, collect, and measure. During the early nineteenth century, one of the few British measurers of magnetic phenomena was George Gilpin. Gilpin, who served as an astronomical assistant on Cook's second voyage and afterwards as an assistant at the Royal Observatory (1776-81), recognized the lack of activity and called for increased magnetic observations. In 1806, he noted as Clerk of the Royal Society that magnetic observations made for only limited periods were "not sufficient for minute purposes." Similar Mountaine and Dodson fifty years earlier, Gilpin regretted that eighteenth-century travelers had not made more accurate, land-based observations with proper instruments in different parts of the world. Claiming that progress in terrestrial magnetic theory depended upon carefully registered, properly arranged observations with good instruments, he concluded, "It is hoped therefore, that in future attention to this subject will not be thought beneath those who may have it in their power essentially to promote an undertaking so interesting to the philosopher, and so valuable and useful to the maritime world."
Illustrating a continuing lack of interest in land-based magnetic collecting was the private magnetic observatory of Colonel Mark Beaufoy at Bushey Heath, the only one of its kind in Britain. Between 1813 and 1822, Beaufoy collected land-based observations superior in accuracy and extent to most earlier British work. Carefully recording dip and variation, as well as meteorological data, he complained in 1820 of the dearth of activity:
The only [magnetic] observations which, I believe, have been published are those of the Royal Society, commenced by the late Mr. Gilpin, and continued by the present librarian; but notwithstanding the accuracy of the former, and the well-known scientific abilities of Mr. Lee, these observations being made in a room in which iron has been used to strengthen the ceiling (and not in the open air), it is doubtful whether the real variation can be truly ascertained.
Indeed, Beaufoy knew of only two places where land-based magnetical observations were being made. Both Gilpin's and Beaufoy's remarks indicated a prevailing lack of interest with respect to land-based magnetic observations.
By the late 1810s, the renewed search for the North-west Passage fostered the global collection of terrestrial magnetic data, particularly in seeking the supposed location of the magnetic pole or poles. Arctic exploration raised the importance of magnetic measurement to a level unimagined in the days of Captain Cook. Since Elizabethan times England had sent expeditions in search of the North-west Passage. Following the Revolutionary and Napoleonic wars, the Royal Navy sought new challenges and employment for its swelled ranks. By 1817, ninety percent of Britain's naval officers, six thousand in number, remained unemployed or under employed. A possible avenue for their employment and promotion came in 1816-17, when whalers reported comparatively ice-free seas near Greenland. Remarking of a whaling voyage, experienced whaler, William Scoresby, Jr., noted "a remarkable diminution of the polar ice had taken place, in consequence of which I was able to penetrate in sight of the east coast of Greenland . . . A situation which for many years had been totally inaccessible." Replying to an inquiry from Joseph Banks, Scoresby supposed that "the mystery attached to the existence of a north west passage might have been resolved" if his had been an expedition of discovery. However, Greenland whalers such as Scoresby took an oath preventing them from such exploratory ventures.
Excited by the renewed possibility of discovering the North-west passage, Banks wrote to the First Lord of the Admiralty, Lord Melville, about the unusually ice-free seas. Advancing arguments similar to Banks', the second secretary of the Admiralty, John Barrow, added the factor of Russian activity in the Arctic. In October 1817, Barrow commented, "The Russians have for some time been strongly impressed with the idea of an open passage round America. . . . It would be somewhat mortifying if a naval power but of yesterday should complete the discovery in the nineteenth century, which was so happily commenced by Englishmen in the sixteenth." Adding fuel to the fire, Barrington's arguments from the 1770s were republished in 1818.
In response to pressure from the Royal Society and the Admiralty, Parliament's passage of the Longitude Act of 1818 gave immediate impetus for renewed British exploration. Amending the Acts of 1743 and 1776, this legislation supplemented the full reward of £ 20,000 with a graduated scale of awards for sailing further north or westward. Sailing to north latitudes of 83°, 85°, 87° and 88° earned £1000, £2000, £3000, and £4000 respectively. Similarly, £5000, £10,000, and £15,000 would be awarded for sailing west from Greenwich, 110°, 130°, and 150° within the Arctic Circle (i.e., 66 1/2° N). These large rewards spurred naval officers to explore the frozen, inhospitable polar regions.
In addition to opportunities for professional advancement and pecuniary payoff, many argued that Arctic voyages would benefit numerous areas of science, including the study of magnetism. During the late eighteenth century, Greenland whalers and navigators including Phipps and Cook had described the unsteady movements of the compass, the increase of dip, and the large variations of high latitudes. Arising from these observations as well as theoretical considerations, natural philosophers supposed the existence of a northern magnetic pole, yet remained unsure of the pole's position and possible movements. For example, Euler placed the north magnetic pole at 75° north, 115° west longitude from Paris, while Buffon positioned it at 71° north, 100° west, and French observational astronomer Jerome Lalande put it at 77° 4' north, 86° west. In the 1790s, American John Churchman traveled to France, but failed to persuade the French government to fund a voyage to determine the magnetic pole's position. In 1802, Lalande lamented the lack of proper magnetic data for locating and calculating the motion of the magnetic pole.
With the renewed possibilities of Arctic exploration following the Napoleonic wars, British investigators showed increasing enthusiasm for collecting scientific observations, including magnetic data, in far northern latitudes. In 1815, Scoresby read a paper to the Wernerian Natural History Society proposing a trip to the north pole. An outline of his forthcoming book on Greenland included sections describing the polar seas, ice, atmosphere, and fauna. Scoresby's proposed appendix contained a series of meteorological and magnetic tables. Explaining the opportunities provided by Arctic research two years later, Mark Beaufoy contended that the collection of measurements of the depth, temperature, and salinity of the sea, as well as meteorological data "would contain much interesting and valuable information, and throw great light on the natural phenomena of these unexplored regions." Of magnetism, he specifically noted that the
extraordinary declination of the compass (peculiar to this part of the world) is so remarkable, that, were a vessel sent for no other purpose than of making magnetical observations, both time and money which might be bestowed on the expedition would be advantageously employed for the advancement of science.
Beaufoy also conjectured that variation continued to increase in higher latitudes until the needle lost all its polarity. Though his proposal for an exclusively magnetic expedition did not come to fruition, Beaufoy's comments regarding unusual compass behavior in Arctic latitudes were frequently repeated by later investigators.
In addition to strange compass behavior, some speculated about the connections between terrestrial magnetism and other polar phenomena. Remarking on the recent disappearance of ice, a writer in the Philosophical Magazine noted in 1818:
Whether there exists any combination of causes— whether the connexion is between the ice and the grand focal point of magnetic attraction, which some philosophers suppose to be situated in the earth, or whether it is between the ice, and electricity in the atmosphere, or the aurora borealis, or all these together, can as yet be only a matter of mere conjecture.
Though such speculations did not gain much attention until the 1820s, Scoresby, Beaufoy, and others placed greater emphasis on magnetic observations than had investigators of the previous century.
In their quest to explore and measure, British advocates of Arctic research gained enthusiastic and powerful support from John Barrow of the Admiralty. In 1818, Barrow lamented the lost opportunities for observation during a recent voyage:
The arctic regions are at this moment, from many circumstances, so peculiarly interesting, that we took up the present volume in the hope of meeting with some new or striking observations on the geography, hydrography, or meteorology of a part of the northern seas which of late years has not been much visited by men of nautical science; but we have been disappointed . . . In the 'Voyage to Hudson's Bay' there is literally nothing worth communicating to the public at large.
Despite disappointments, Barrow asserted that forthcoming polar expeditions planned to collect much data "interesting and important to science," including the state of atmospheric electricity and its connection with magnetic inclination, declination, and intensity; these facts alone "would be worthy a voyage of discovery." Recognizing that the polar regions were the location of the north magnetic pole, Barrow noted that comparing polar and equatorial magnetic measurements might also lead to important results. Furthermore, he called for additional investigations of the temperature, depth, salinity, and specific gravity of seawater; velocity and direction of ocean currents; and pendulum experiments to determine the figure of the earth.
While indicating the growing role of science, Barrow's comments also illustrated links between scientific achievement and national prestige. In A Chronological History of Voyages into the Arctic Regions (1818), Barrow explained that if the initial searches for the North-west passage should fail,
from both [voyages] may at least by confidently expected much valuable information, and improvement in the hydrography and geography of the arctic regions; as well as many important and interesting observations on the atmospherical, magnetical, and electrical phenomena, which cannot fail to advance the science of meteorology; and lastly, many valuable collections of objects in natural history . . . Of the enterprize itself it may be truly characterized as one of the most liberal and disinterested that was ever undertaken, and every way worthy of a great, and prosperous and an enlightened nation; having for its primary object that of the advancement of science.
Following the advice of Barrow and others, the Arctic voyagers' official instructions directed them to make measurements and observations of all kinds. Compared with similar eighteenth-century efforts, scientific concerns took an increasingly prominent role. Terrestrial magnetism clearly played a larger role in these efforts.
The Initial Voyages (1818): John Ross and David Buchan
Though a variety of geographic, national, economic, and scientific concerns contributed to the renewed British quest for the North-west passage and the North Pole, Arctic exploration directly stimulated magnetic collecting and interest in terrestrial magnetism as well. Receiving much scientific advice from the Royal Society and enthusiastic support from Barrow, the Royal Navy launched a series of Arctic expeditions. In 1818, two expeditions set sail with Captain John Ross seeking the North-west passage in H. M. S. Alexander and Isabella, and Captain David Buchan attempting to reach the North Pole in H. M. S. Dorothea and Trent.
Reminiscent of eighteenth-century expeditions, British polar exploration gave renewed opportunity for collecting global magnetic measurements. The continuing partnership between the Royal Society and the Admiralty betrayed an increasing stress on magnetic collecting. For example, in November 1817, the Royal Society recommended to the Admiralty a voyage to the North Polar regions specifically to collect magnetic measurements. Illustrating magnetism's importance, Ross' official instructions from the Admiralty noted:
Amongst other objects of scientific inquiry, you will particularly direct your attention to the variation and inclination of the magnetic needle, and the intensity of the magnetic force; you will endeavour to ascertain how far the needle may be affected by the atmospherical electricity, and what effort may be produced on the electrometer and magnetic needle on the appearance of the Aurora.
The Admiralty repeated these same instructions to several subsequent voyagers.
As in earlier efforts, Ross' expedition carried a great variety of instruments to measure wind, water depth, temperature, air pressure, humidity, atmospheric refraction, and magnetic phenomena. The Isabella carried at least four dipping needles by different instrument makers, twelve compasses of various types, and numerous books containing the astronomical and magnetic data from previous voyages. The appointed astronomer, Captain Edward Sabine (1788-1883) of the Royal Artillery, was told to assist Ross "in making such observations as may tend to the improvement of geography and navigation, and the advancement of science in general." Sabine, a skilled observer educated at the Royal Military Academy, Woolwich, had been elected F. R. S. in 1818. He came highly recommended by Joseph Banks and the Council of the Royal Society. Sabine later became one of the major figures in the British study of geomagnetism in the 1830s and 1840s. We will return to his early magnetic research shortly.
Despite the growing prominence of the goal of magnetic data collection, Ross' remarks in A Voyage of Discovery . . . Inquiring into the Probability of a North-West Passage (1819) illustrate the continuing role of navigators as mere collectors of data. As he explained, "the following Article, on the Variation of the Compass and Deviation of the Magnetic Needle, is not offered as a contradiction or a confirmation to any theory which has been already adopted;—the author has all along considered himself as a collector of facts only." Reiterating practical concerns of earlier navigators, Ross remarked that the compass:
should be rendered as unerring a guide as possible; and this can only be done by a certain universal and invariable mode of finding the true variation, at all times and places, and under all circumstances.
This variation of the compass being one of the important objects of the Expedition under my command, it became my duty to examine the various reports and publications on the subject, and to endeavour to ascertain how far the different systems given to the Public are correct; and the rules for correcting the deviation of the variation to be depended on.
Building upon the work of Flinders, an appendix to Ross' book carefully described experiments on the local attraction of the Alexander and Isabella.
Ross' second in command, William Edward Parry (1790-1855), also showed great enthusiasm for the study of magnetism. During the voyage with Ross and several later attempts to find the North-west passage, he assiduously collected magnetic data. Early in 1818, before Ross' ships had left from England, he wrote to his parents:
The observations upon the magnet will form one of the most interesting objects of the expedition. A variety of compasses are prepared for us, and great expectations are formed of the results we are likely to obtain in high northern latitudes. The connection observed, in many instances, between magnetism and electricity, and between these and the Aurora Borealis, is very curious, and it is expected, that the observations we shall be enabled to make, may throw considerable light upon it. There are great speculations on foot, as to what effect may be anticipated upon our compasses, when we approach the Magnetic Pole.
Parry's remarks show great enthusiasm for magnetic research unlike any of his eighteenth-century predecessors. During the voyage he excitedly remarked on unusually large variations and probable proximity of the magnetic pole. In a letter to Barrow, Parry exclaimed, "the Variation had increased to 89°!!— the Dip is 84° 25'. I suppose, therefore, that the data we send you officially will be sufficient for finding the bearings and distance of the Magnetic Pole at once." Parry's other explorations will be examined later in this chapter.
Ross' 1818 voyage, like those of Cook and Phipps, failed to find a North-west passage. Quickly retreating from Lancaster's Sound due to a vast mountain range (he named the Croker Mountains) which apparently only he saw, Ross returned home to severe criticisms from Barrow and several officers, including Parry and Sabine. Objecting to Ross' retreat, Sabine recalled his "very visible mortification at having come away from a place which I considered as the most interesting in the world for magnetic observations, and where my expectations had been raised to the highest pitch, without having had an opportunity of making them." Furthermore, Sabine objected to Ross taking credit for certain magnetic observations. In one instance, Ross had refused to let Sabine take the dipping needle ashore because he did not wish to be detained by observations. Sabine also accused Ross of stealing magnetic measurements without giving him credit.
Later in 1819, Ross responded to Sabine's accusations in a short essay. Noting that Sabine did not have an exclusive right to publish observations made during the voyage, he explained that several officers, including himself, assisted in making observations and that they were frequently recorded by different persons. Of Sabine's charges of inaccuracy, Ross remarked, "with respect to the magnetic observations, I have only to observe, that although they may differ from Captain Sabine's, they are clear of the imputations bestowed upon them; and it will hereafter be made to appear, whether Captain Sabine's observations or mine are most likely to be incomplete, imperfect, or incorrect." While this exchange reflected personal animosity between Ross and Sabine, it also hinted at the increasing importance attached to accurate magnetic observations.
Quickly reporting measurements of variation, dip, and intensity to the Royal Society, Sabine also published investigations on the effects of local attraction in the Philosophical Transactions. Noting that the compasses on each ship disagreed with one another by 3° to 8°, Sabine sought to find the precise nature of these errors. He followed Flinders' procedure of fixing the location of the compass and swinging the ship to determine points of no compass deviation (or points of no error). Swinging the ship required steadying it on each point of the compass and recording magnetic bearings of a distant object. At the same time, a compass taken a sufficient distance from the ship (usually on the ice) insured that measurements were free from local attraction. Agreement between sets of bearings taken on and off the ship indicated the points of no error, while discrepancies illustrated errors arising from local attraction.
Although Sabine viewed his work as confirmation and extension of Flinders', he stressed the need for the multiplication and repetition of observations. Regarding hourly changes in declination he asserted, "careful observations on the direction of the needle at different hours of the day, on all convenient occasions, might be more serviceable towards a more certain knowledge of its causes." He also noted that the relationship which Flinders discovered between local attraction and dip had not taken into account the diminution of directive force as the dip increased. Such a diminution, Sabine believed, explained the sluggish movements of compasses in high latitudes. As had earlier magnetic collectors, Sabine generally avoided theoretical discussion in his writings. Suspicious of hypotheses throughout his career, he remained convinced that amassed observations would eventually lead to the true theory of terrestrial magnetism. Local attraction hindered Sabine's empirical approach because in higher latitudes it "rendered observations on board ship of little or no value towards a knowledge of the true variation." Hence, compass deviations due to ship magnetism resulted in both practical and theoretical considerations. Unlike the previous century, local attraction required investigators to go off their ships and collect magnetic data.
In general, extensive polar exploration helped to make magnetism an area of greater interest than in the eighteenth century. Ross, Sabine, Parry, and numerous other Arctic explorers were continually fascinated by the odd behavior of the compass, the effects of local attraction, and the possibility of locating the magnetic pole. For instance, Ross' assistant surgeon, Alexander Fisher, remarked that although the principal object of the voyage was to find the North-west passage, there were several others deemed important such as finding where the magnetic pole is situated and observing pendulum vibrations in high latitudes. Since icebergs often afforded the opportunity to make observations free from local attraction, delays caused by ice blockage, he contended, were no longer wasted time. Also in his account, Fisher discussed Parry's numerous experiments on local attraction.
Like Ross' voyage in 1818, the North Pole expedition led by David Buchan was instructed to carefully observe magnetic variation, dip and intensity. Frederick Beechey, an officer serving with Buchan, later noted that:
The peculiarity of the proposed route afforded opportunities of making some useful experiments on the elliptical figure of the earth; on magnetic phenomena; on the refraction of the atmosphere . . . and on the temperature and specific gravity of the sea at the surface, and at various depths; and on meteorological and other interesting phenomena.
Like Sabine, the voyage's astronomer George Fisher of Cambridge University recorded observations of magnetic dip, variation, and intensity. A journal from the voyage noted the sluggishness of the compasses and recorded, "we must now be crossing the Magnetic Pole fast, as the variation increases so much." Similar compass behavior and magnetic readings were observed in many Arctic voyages.
Despite failing to find the North-west passage or reach the North Pole, the 1818 voyages of Ross and Buchan provided a template for additional assaults on the Arctic. During the 1820s and 1830s, attempts continued carrying large contingents of men heavily outfitted for Arctic travel. Though the allure of discovering the North-west passage continued to overshadow all other goals, scientific objectives gained more attention than previously. Admitting the primary objective, Parry conceded in 1821 that "the improvement of geography and navigation, as well as the general interests of science, were considered as of scarcely less importance." In contrast to Phipps' complaint that scientific observations had received only secondary consideration, Parry's comments indicated their newly-elevated importance. Though astronomy, meteorology, and natural history continued to receive much attention, magnetism also gained great notice.
The Search Continues (1819-1829): W. E. Parry and John Franklin
Emerging from the controversy regarding Ross and the Croker Mountains, in 1819 Parry gained command of an expedition to find the North-west passage aboard H. M. S. Hecla and Griper. The Admiralty yet again instructed Parry and Sabine to pay particular attention to magnetic measurements as well as interactions between the magnetic needle, atmospherical electricity, and the aurora borealis. Their official orders also called for magnetic data collection along the western shores of Baffin's Bay, near the supposed position of
one of the great magnetic poles of the earth, as well as such other observations as you may have opportunities of making in Natural History, Geography, &c., in parts of the globe, &c., little known must prove most valuable and interesting to the science of our country; and we, therefore, desire you to give your unremitting attention, and to call that of all the officers under your command, to these points, as being objects likely to prove of almost equal importance to the principal one . . .
Compared with instructions for earlier Arctic voyages, the Admiralty's instructions suggested a higher priority on science in general, and on magnetism in particular.
As they had during Ross' 1818 voyage, Parry, Sabine, and other officers meticulously collected magnetic data and recorded the effects of local attraction. Like many of his predecessors, Parry asserted his role as a collector of facts:
The extent of my aim has been, to give a plain and faithful account of the facts which I collected, and the observations which were made by myself and others, in the course of the voyage; and these, as far as they go, may be relied on as scrupulously exact. It is for others, better qualified than ourselves, to make their deductions from those facts.
In line with this ideal, Parry's account of the voyage included numerous tables of magnetic variation, dip, and intensity. He made no attempt to interpret the amassed data; that was not his job. Parry, with the help of Sabine and several others, made repeated, independent measurements, often with different instruments. Most observations were performed in portable observatories on ice or land, away from the ship's influence. Though Parry succeeded in removing the Croker Mountains from the map and pushing further west than any other expedition for many decades to follow, he nevertheless failed to discover the illusory passage.
While none of the attempts during the 1820s and 1830s achieved the prized goal of the fabled passage, they continued extending geographic knowledge and collecting scientific data. Referring to comparative measurements of magnetic intensity, Captain Sabine reported in 1825:
M. de Humboldt's experiments, with a much fewer number made by M. Rossel . . . include it is believed, the whole of our experimental knowledge in regard to intensity, previously to the year 1818; when the determination of the British government to re-attempt the discovery of a North West Passage . . . opened a field of great interest for researches of every kind connected with magnetism, in countries to which the access had previously been extremely inconvenient.
Such sentiments clearly linked the renewal of Arctic exploration with increased opportunities to study terrestrial magnetism. In particular, unusual compass behavior, local attraction, and the possibility of locating the magnetic pole attracted the attention of many polar explorers and natural philosophers. Noting sluggish compass movements, Alexander Fisher, ship's surgeon on Parry's first voyage, reported that the directive power of terrestrial magnetism decreased upon approaching the magnetic pole causing the effects of local attraction to increase. From this, he supposed the proximity of the magnetic pole. Similar remarks appeared in a set of anonymous letters written during Parry's first expedition of 1819-1820. Reiterating the difficulties of compass usage in high latitudes, these letters pointed out the probable proximity of the terrestrial magnetic pole. They also reiterated the necessity of measuring variation and dip away from the ship's influence. Illustrating the persistent link between the study of magnetism and navigation, the writer asserted that "among the mysteries of nature by which men are environed, none is more interesting, because none is more essential to the navigator than the powers and the properties of the magnet."
However, while the connection between magnetism and navigation remained intact, it was no longer the primary reason that natural philosophers showed interest in magnetism. With many of the earlier navigational problems solved, more purely scientific concerns took a larger role in the nineteenth century than in the previous century. In February 1819, for instance, Barrow reiterated the scientific benefits of Arctic exploration, particularly those related to magnetism:
In the late Expedition for exploring a passage from the Atlantic to the Pacific Ocean, many observations were made of a nature highly interesting to Science, and, among others an extraordinary and unlooked for degree in the variation of the Magnetic Needle, from which it is more than probable that the direction of the Copper-Mine River . . . and the point where it discharges itself into the Northern Ocean are very erroneously marked down on the Charts.
Stressing the defective geography of Samuel Hearne's earlier land expedition (1769-1772), Barrow desired that the Admiralty assign "an officer well skilled in astronomical and geographical science, and in the use of instruments" to command an overland voyage. The officer chosen for the trek across the North American wilderness was Captain John Franklin (1786-1847).
Franklin had gained much experience in observing and collecting. In 1801, when only fifteen years old, he began a long career of exploration aboard the Investigator commanded by Captain Flinders. After naval service in the Napoleonic wars, Franklin had been second-in-command during Buchan's failed attempt to reach the North Pole in 1818. A year later, for his first land expedition (1819-22), Franklin was instructed:
You will also not neglect any opportunity of observing and noting down the dip and variation of the Magnetic needle, and the intensity of the Magnetic force, and you will take particular notice whether any, and what kind of degree or influence the Aurora Borealis may appear to exert on the magnetic needle. . . . The two Admiralty Midshipmen are to be employed in assisting you in all the observations above mentioned, and you will direct them to keep a register of them, and also accurate journals of all proceedings and occurrences.
Despite great hardships during this voyage, Franklin and his men faithfully followed their instructions, amassing a multitude of observations including those of magnetic variation, dip, and intensity. To obtain magnetic intensity or force, he counted the vibrations of a freely swinging dipping needle. However, despite ongoing attempts to improve magnetic instruments, navigators continued complaining. Franklin remarked that the instrument "was not of the best kind for making with accuracy such delicate observations, and our results may, perhaps, be considered as only approximations to the truth."
Accompanying efforts to make better instruments, the quest continued for more complete and standardized magnetic measurements. Though less successful than his first voyage (which reached 110° W longitude and claimed the £ 5,000 prize), Parry's second (1821-23) and third (1824-25) expeditions in H. M. Ships Hecla and Fury amassed valuable scientific data. Reverend George Fisher replaced Sabine as the astronomer on the second voyage, but the official instructions repeated, verbatim, the advice regarding magnetic variation, dip, and intensity. Seeking standardization, the Admiralty wanted Fisher "to be particularly careful to keep an accurate register of all the observations that shall be made, precisely in the same forms, and according to the same arrangement, that were followed by Captain Sabine on the late voyage."
Beyond the attempts to improve instrumentation and standardization, the scope and intensity of magnetic collecting changed as well. During Parry's third voyage, the work of Parry and Lieutenant Henry Foster, Fisher's replacement, clearly illustrated the growing complexity of Arctic magnetic research. Of observations made ashore during the winter of 1824, Parry noted, "The interest of these, especially of such as related to magnetism, increased so much as we proceeded, that the neighborhood of the observatory assumed, ere long, almost the appearance of a scattered village, the number of detached houses having various needles set up in them, soon amounting to seven or eight." With the availability of more sensitive instruments, investigators became increasingly interested in small variations of magnetic variation and intensity. In addition to the standard magnetic observations, Parry and Foster took regular hourly observations with newly-introduced suspended needles. As well they performed magnetic experiments designed by Peter Barlow and Samuel Hunter Christie, mathematics professors at the Royal Military Academy, Woolwich. The researches of Barlow and Christie will be examined in chapter six.
As previously mentioned, in the 1820s, Parry and other British began using French measuring techniques and instruments to determine relative magnetic intensity. Since the 1780s, French physicists including Jean Charles Borda and Charles Augustin Coulomb had used silk-suspended rather than pin-supported needles for sensitive observations of magnetic intensity and diurnal variation. Recording the time it took for a set number of the needle's oscillations determined relative magnetic intensity. This technique, however, was not widely utilized by the British until the reawakened interest in magnetism which accompanied renewed Arctic exploration. With delicately suspended needles, Arctic explorers and other investigators could record smaller and more transient phenomena than their predecessors. Parry, for instance, noted a diurnal change in intensity which regularly increased from morning to afternoon and decreased from afternoon to morning. Of these changes, he speculated in 1826:
It also appeared that the sun, and, as we had reason to believe, the relative position of the sun and moon, with reference to the magnetic sphere, had a considerable influence both on the intensity and diurnal variation, although the exact laws of this influence may still remain to be discovered.
Repeating this suggestion in the Philosophical Transactions, Parry and Foster wrote, "when any extraordinary change, however, appeared to be going on, the needles were more closely watched; and every phenomenon, such as the aurora borealis, meteors, clouds, the kind and degree of light, the moon's position, and the temperature within and without, were at all times carefully noted." Despite the search for connections between various phenomena characteristic of natural philosophers during the 1820s, Parry and Foster warned that such questions were "of great delicacy, and of intricate research, and will be best left to the investigations of those who are theoretically conversant with these subjects." Hence, the division between navigators and natural philosophers persisted.
In addition to doing experimental research and collecting magnetic data, investigators continued to exhibit great interest in improved instrumentation. Early in 1821, Captain Henry Kater (1777-1835) devoted his Bakerian lecture to the optimum shape and kind of steel for making compass needles. Recognizing the compass problems during Ross' first expedition, Kater wanted Parry's first expedition to have magnetic instruments which combined "as much power and sensibility as possible." Indicating the impact of French experimental physics, he employed Coulomb's torsion balance, repeated some of Coulomb's experiments, and cited Jean-Baptiste Biot's improved method of magnetizing needles. Arising from his research, Kater produced what became the standard azimuth compass in the navy. Like Knight's azimuth compass in the eighteenth century, Kater's highly regarded instruments were widely used in the nineteenth century. Parry, for instance, explained after his first voyage, "it is therefore deserving of especial notice, that even in such extreme circumstances, Captain Kater's excellent compasses, when used on shore, and with patience and attention to frequent tapping, indicated the meridian with very tolerable precision." In sum, Kater's research utilized French techniques and responded to the changing needs of Arctic exploration; thereby he produced instruments considered better than their predecessors.
Also desiring improved instrumentation, Sabine commented in 1822:
the consequent advance which has been made in this branch of natural knowledge [magnetism], render it desirable, that a greater degree of accuracy should be obtained in all respects, in observing its various terrestrial phenomena . . . This remark applies especially to observations on the dip of the needle; the instruments in general use for this purpose have received little or no improvement during the last fifty years, and produce results which can only be considered as approximate.
In 1825, Sabine's remarks further illustrated the increasing observational emphasis on dip and intensity, and their links to new instrumentation. These measurements, previously of less interest because they lacked direct importance to navigation, became the primary measurements for exploring terrestrial magnetism after the 1820s. Sabine attributed changes in magnetic intensity to either a fluctuation in the earth's magnetic intensity or the shifting positions of the terrestrial magnetic poles. Experiments indicated that geographical variations in intensity could not be represented by any function of the dip. Hence, magnetic intensity must be regarded "as an essential element of the computation, distinct from the dip, and necessary to be known by observation." In this, Sabine and others illustrated a growing interest in observing intensity as a distinct magnetic component. The emphasis on observations which lacked direct relevance to navigation and also required different types of instrumentation demonstrated a growing curiosity in terrestrial magnetism for its own inherent scientific interest.
In addition to practical, theoretical, and instrumental concerns, national pride played a prominent role in global magnetic collecting. Remarking on Parry's first voyage, retired army colonel John Macdonald noted in 1822 that beyond the discovery of the North-west Passage bestowing "a new wreath to the naval crown of Great Britain," Parry's close approach to the location of the magnetic pole added to the "honour of our country." Others agreed that locating the magnetic pole would increase British national and scientific prestige. A dozen years later, Commander James Clark Ross (1800-1862), John Ross' nephew, asserted magnetism to be an "eminently British" science. Reporting magnetic observations gathered during a privately-funded expedition led by his uncle (1829-33), Ross boasted in 1834:
Their is no other country in the world whose interests are so deeply connected with it [magnetism] as a maritime nation, or whose glory as such is so intimately associated with it, as Great Britain. All the late discoveries and improvements are to be attributed to the perseverance of British science, and the encouragement and assistance of an enlightened and liberal Administration . . . enabling a few British seamen to plant the flag of their country upon the Northern Magnetic Pole of the earth.
As with his uncle's earlier claims regarding the Croker Mountains, James Clark Ross' claims to have located the northern magnetic pole did not pass without controversy. In addition to mounting a later expedition to find the south magnetic pole, J. C. Ross, along with Sabine, was a major instigator of the "Magnetic Crusade" of the 1830s. In fact, Ross spent most of his time between 1834 and 1838 making a magnetic survey of Great Britain and Ireland by the order of the Admiralty. We will return to these developments in the final chapter.
In 1838, at a meeting of the British Association for the Advancement of Science, another officer in the Royal Navy expressed similar nationalistic sentiments about polar exploration. Claiming that all of Europe looked to Great Britain to solve the problem of terrestrial magnetism in the southern hemisphere, Captain Washington patriotically remarked:
Under a deep and abiding conviction that our country's future glory is identified with the encouragement of British enterprise, and that she would lose her high national character by ceding to another this opportunity of completing the work first traced out by Cook, I could not refrain from recording my sentiments, and conclude with the ardent hope that through the exertions of the British Association our wishes may be realized, and that ere long the southern cross may shine over an expedition sailing to the Polar Seas . . . and that cross . . . will once again shine over 'the meteor flag of England,' proudly waving over Antarctic land, discovered by the zeal and intrepidity of British seamen.
Such sentiments linked British nationalism to polar exploration and scientific achievement. Of numerous British scientific and geographic accomplishments during the 1820s and 1830s, those related to terrestrial magnetism took a more prominent position than they had in the preceding century.
The patriotic comments of Ross, Washington and others also strongly identified polar explorations with the extension of natural knowledge. Since the days of Cook, these voyages had pursued the global collection of geographic, hydrographic, meteorological, zoological, and geomagnetic data. Among these observations, the previously tangential concern for magnetic collecting in the eighteenth century gained prominence in the nineteenth century. As has been shown, the recognition of local attraction and renewed Arctic exploration contributed to this shift.
The immense task of meticulously collecting magnetic data particularly suited the Royal Navy because they already possessed the necessary equipment to gain access to the frigid polar regions and the military discipline required to make repeated measurements under extremely harsh conditions. Similarly, the Royal Artillery possessed the order and organization necessary for later land-based surveys and the permanent geomagnetic observatories established in the 1830s. First and foremost, collectors of magnetic data such as Ross, Sabine, Franklin, Parry, and Foster were scientific servicemen. By and large, these militarily-employed investigators retained a role as collectors of facts, infrequently attempting to interpret the amassed data. Changes in instrumentation and technique indicated a continuing concern for precision, but also illustrated the importance of different kinds of measurements in the nineteenth century. In particular, magnetic dip and intensity garnered much more attention for their supposed theoretical value.
In addition to scientific servicemen, British natural philosophers and mathematicians became increasingly interested in terrestrial magnetism in the 1820s for a variety of reasons. The division of labor continued, with navy officers collecting magnetic observations, and natural philosophers and mathematicians trying to interpret the data within a theoretical framework. As well, men of science performed numerous experiments on isolated magnets and magnetic materials and compared their results with the data amassed from the entire earth. Comparing controlled experiments with terrestrial data resulted in speculations about the origins of magnetism and the laws of terrestrial magnetic change. The work of these physicists and mathematicians, however, will be discussed in the final chapter. Hence, with the general scope of magnetic collecting laid out, the next chapter examines British theories of magnetism beginning in the mid-eighteenth century and their relationship to terrestrial magnetic studies.