Like Bacon, Gilbert emphasized the importance of drawing conclusions from experiments and observations, and rejected the scholastic Aristotelianism. (This did not stop Bacon from accusing Gilbert of having “made a philosophy out of a few experiments,” mostly because he posited the existence of a kind of “magnetic soul” in the earth.)67 Gilbert created a model of the earth—which he called a terrella, for “little earth”—by forming a sphere out of a lodestone, a naturally magnetized mineral. He then devised a versorium, or “turn-detector”—a miniature needle, mounted so it could rotate freely in three dimensions. Moving the versorium over the surface of the terrella, as if it were a ship sailing over the surface of the earth, Gilbert identified the location of the magnetic poles by observing where the needle stood vertically. He also found that the “dip” in the needle increased steadily from zero degrees at the equator to 90 degrees at the poles, which he realized could be an accurate way to determine latitude while at sea.68
By the time Herschel became interested in terrestrial magnetism, it was recognized that the earth’s magnetic north pole did not correspond to the geographic North Pole. So the mariner navigating by compass needed a way to calculate how far off geographic north was from the magnetic north to which his compass pointed. Now we know that the earth’s magnetic field is “inclined” at about 11 degrees from the axis of rotation of the earth (the magnetic poles also shift over time, about two degrees every century, because of the shifting of the molten core of the earth). The difference between true geographic north and magnetic north is called declination, and it differs depending on what part of the globe you are measuring from. Maps showing the magnetic declination in various locations resemble Whewell’s tide maps, with their curvy lines connecting different spots on the earth sharing the same declination, and they are used even today by airplane pilots deciphering the readings of a plane’s compass.69
Herschel shared the belief held by other prominent scientists, such as Humboldt, Arago, and Faraday, that atmospheric disturbances and the earth’s magnetic field were closely related, and that understanding the patterns of magnetic force around the globe would help in predicting weather phenomena. They disagreed with the view of the famous mathematician and physicist Carl Friedrich Gauss that the earth’s magnetic field had only a terrestrial component, with no influence from cosmic sources. Faraday and others were then showing the intimate connection between electricity and magnetism, a connection that seemed to confirm the view that terrestrial magnetism and atmospheric electricity were interrelated. C. C. Christie’s discovery in 1831, based on work done by Humboldt and Biot, that there was a clear connection between the aurora borealis and the earth’s magnetic field—a result discussed at the British Association meeting in Cambridge in 1833—reinforced this position.70 The earth’s magnetic field attracts particles from outer space, much as a bar magnet attracts iron filings. Particles from the sun enter the atmosphere near the poles, where they collide with oxygen molecules in the air. The energy released by these “excited” oxygen molecules is visible as a greenish blue glow: this is the phenomenon of the polar auroras, known as the aurora borealis in the northern hemisphere and the aurora australis in the southern hemisphere.
The goal of magnetic research was to find a theory that would express the variation of the earth’s magnetic field in terms of simple laws—just like the kinds of tidal laws Whewell was seeking. Such laws would be valuable for navigation, in explaining and predicting the variation of the mariner’s compass, for example. Herschel and Whewell’s friend Francis Beaufort realized that the discovery of the laws of terrestrial magnetism would greatly improve the British navy’s ability to find its way across the seas. As he had pushed for Whewell’s international tide project within the British Admiralty, Beaufort now began to lobby for governmental support for an international program of magnetic research.
But scientists also hoped that the results of such an undertaking would shed light on the nature of the universe’s fundamental forces. As Harcourt put it in his speech at the 1839 British Association meeting at Birmingham, success in this endeavor would lead to “a completion of what Newton began—a revelation of new cosmical laws—a discovery of the nature and connexion of imponderable forces.”71 This search soon became known as the “great magnetic crusade.”
Proponents of studying terrestrial magnetism had a twofold agenda. First, they desired to set up what Herschel called “physical observatories” throughout the globe that could make simultaneous observations over a wide range of the earth’s surface for long periods. Whewell’s tidal research had shown that such international cooperation was possible, and that it could lead to important results. These physical observatories could conduct observations of the magnetic field’s intensity, declination (the difference between true north and magnetic north), and inclination (the angle between the vertical direction of the field and the horizon measured in the plane of magnetic north).72 The observatories would also take meteorological readings, which could then be compared to the magnetic data; for this task the observatories could avail themselves of a new device invented by Whewell, the self-registering anemometer, which measured the quantity and direction of the wind.73
At the Paris Observatory, under the supervision of Arago, geomagnetic research had been conducted for decades. The Göttingen Magnetischer Verein (the “magnetic union”), a system of magnetic observatories throughout Germanic Europe, had been founded by Gauss and Wilhelm Weber in 1834. England was falling behind. Those involved with the magnetic crusade in Britain were convinced that if Britain did not act soon, the honors would go to the French or Germans.74 (Although other men of science generally derided Babbage’s Decline of Science, they did share his fear that Britain would lag behind the Continent.)
The second prong of the magnetic crusade was a “roving magnetic observatory”—an expedition to the South Polar regions to find the south magnetic pole. One of the leading proponents of this expedition was Edward Sabine, who had borne the brunt of Babbage’s ire in his Decline of Science. Right after his election to the Royal Society in 1818, the Irish-born artillery officer was invited to take part in the first Arctic expedition of Captain John Ross. The principal purpose of the expedition was to find the elusive “Northwest Passage” to the Pacific Ocean, an east-west sea lane between the icy islands of British Canada. But it was also hoped that while on board Sabine would discover the magnetic north pole. Both missions ended in failure; Ross turned back after finding his progress blocked by sea ice.
The following year, Sabine returned to the Arctic as part of William Parry’s expedition to seek the fabled passage. Parry failed as well, though he did go farther west than had any other ship to that point. During the voyage, Sabine noticed that changes in magnetic intensity had taken place since his last visit. His experiments showing this won him the Royal Society’s Copley medal (which he shared with Herschel that year) in 1821.
Magnetic north was finally discovered by John Ross and his nephew James Clark Ross in 1831. The British Admiralty had refused to provide funding for this expedition, but the two explorers found a private backer: Felix Booth, owner of Booth’s distillery (Booth’s gin is still being made today). Using Booth’s money, the Rosses bought a 150-ton paddle steamer, the Victory, and with favorable weather sailed it to the eastern shore of a long peninsula jutting northward from North America. There, the Victory was stuck in sea ice for the winter. The following summer it managed to move only a few miles, and after the next winter it was stuck again, and the explorers were forced to abandon ship, moving on by sledge to a spot where they were fortuitously rescued by a passing whaling ship. They had failed, once again, to find the Northwest Passage.
While the Victory was wedged in the ice, James Clark Ross conducted a series of careful magnetic measurements, which convinced him that the pole was no more than one hundred miles west of their location. Aided by local Eskimos, he set out toward that spot. When he arrived there, a horizontal magnetic needle, suspended on a silk string, showe
d no preference for any direction, and the dip needle pointed within one minute of arc of the vertical: he had found magnetic north. Ross triumphantly raised the British flag and claimed the land for the British crown.75
But the south magnetic pole remained unfound and unclaimed. At the Cambridge meeting of the British Association in 1833, barely two years after Ross had found the north magnetic pole, a committee was formed to promote the magnetic crusade’s objectives. Whewell and Murchison took control of the committee. In 1835 and again in 1836 the Magnetic Committee lobbied the government for funds to establish magnetic observatories throughout Britain and her possessions, and to fund a magnetic expedition to the Antarctic region. Sabine used a report to the British Association meeting in 1837 to make the case for a government-sponsored expedition. But those attempts were unsuccessful until Herschel returned from South Africa.
When he arrived back in England, lauded as the scientific hero of the nation, it was felt that Herschel’s public support of the magnetic crusade could carry the day. The Irish savant Humphrey Lloyd begged Herschel to present the case for a magnetic expedition to the general council at the British Association meeting in Newcastle in 1838—the meeting Herschel had hoped to avoid by traveling to Hanover right after returning to England from the Cape.76 In the end, Herschel did attend the meeting, and was nominated as head of a committee to lobby the government to support the Antarctic expedition. Whewell, another member of the committee, implored him to write the committee’s report, telling him, “You find time for everything!”77 Whewell himself was still having trouble writing after badly injuring his right shoulder and arm in a riding accident in early spring—recklessly taking his horse along a frozen slope, Whewell suffered the indignity of having his horse fall over, causing them both to slide down the hill. Whewell was in so much pain that he was forced to consult with Sir Benjamin Brodie, the renowned medical doctor and fellow of the Royal Society, who assured Whewell that he would recover use of his arm soon.78
In mid-October Herschel had dinner with Prime Minister Melbourne and Queen Victoria; he reported in his diary that night, “Dined today with the Queen at Windsor Castle where had much conversation with Lord Melbourne about the projected South Polar Expedition.”79 By November, Whewell had raised the issue of the expedition with the Royal Society, which also appointed a committee to persuade the government to fund the voyage. At the same time, the government was feeling pressure from other nations: both the Americans and the French had launched or were about to launch expeditions to find the south magnetic pole. A French group led by Dumont D’Urville had left in 1837, and Charles Wilkes was preparing to command an American crew.80 The race to find magnetic south was on.
This international competition was just what was needed to provoke the British government into action. Official approval was given for the expedition in March, and the following month James Ross was named its commander. Now the final preparations could be made. Ross was given the command of two ships, the Erebus and the Terror. These former bomb vessels had been built to withstand the shock of munitions fire, and had reinforced hulls that made them better suited to traveling in icy regions than other Royal Navy ships. The Terror had already made it to the Arctic and back. Both ships would later be commandeered by Herschel’s friend Sir John Franklin for his fatal Arctic journey in 1845. They set sail for their three-year Antarctic voyage on September 25, 1839.81 Ross was armed with a one-hundred-page volume of procedures for making magnetic and meteorological observations, drawn up primarily by Herschel. Herschel lamented to Whewell that “the affair has eaten up a year of my life!”82
Soon before the expedition set sail, Herschel tried to provide Ross with another technology. Herschel hoped that photography would be used to capture the first fixed images of the landscape, flora, and fauna of the Antarctic region. At the start of August, before Daguerre had made public his method, Herschel wrote to him begging him to share his “beautiful process” with the Antarctic expedition. He asked Daguerre to supply “an apparatus with the proper Camera Obscura and 100 plates properly prepared to receive instructions, and with instructions for its use and for executing the singular and extraordinary process by which you have been able to effect such wonders.” He had heard that Daguerre would soon be revealing the details of his process. Yet “should you wish that instructions should yet remain for some time secret you may send them sealed and may rely on their not being opened until the ships shall have passed the Cape of Good Hope.”83
Although Herschel was trying to cajole Daguerre into providing the equipment and instructions, he was privately annoyed at the thought of Daguerre holding his invention hostage to his attempts at securing a pension. Science was for the public good, he thought, not for private fortune. Herschel himself never applied for a patent for his fixing process, even telling Talbot that he was welcome to include the hyposulphite of soda in his own patent; not only had he no objection to this, but he wished that Talbot would make the process known freely, “either publically or privately.” Indeed, as soon as Daguerre heard of Herschel’s 1839 Royal Society paper, he had added hyposulphite of soda to the description of his own process in his patent application without seeking Herschel’s permission.84
Daguerre ungraciously ignored Herschel’s letter, and did not provide the apparatus. The expedition had already sailed when Daguerre finally disclosed his process to the French public after being promised his pension of six thousand francs a year for life. There was some talk of sending out a faster supply ship with the equipment, but in the end it was decided that the process was too cumbersome for use “in the field.”85
Oddly, Herschel does not seem to have tried to persuade Talbot to provide his own process to the expedition. Nor did Talbot volunteer it. Talbot was a member of the Royal Society’s Committee on Botany to help plan the Antarctic expedition’s work in that area. But Talbot did not even mention to the committee the possibility of his photographic process being employed. At the end of August he sent a note to Ross, explaining why he had not offered the use of his process: “Hearing that you had some intention of making drawings in the Southern regions with the Camera Obscura I would have offered any assistance in my power to you but that I knew you could not possibly spare the time that would be requisite.” Instead, he merely enclosed a “little sketch made with a camera of my house in the country.”86 The geologist William Buckland told Talbot that he had convinced Captain Ross to take “several Cameras to make Photogenic drawings of scenery &c. which he may visit.” The expedition’s naturalist, Robert McCormick, called on Talbot and spent some hours talking with him about the new process. But in the end no cameras were taken on the voyage, and the world lost the opportunity to have the first photographs of the Antarctic region.87 At this point, Talbot had not yet made his breakthrough allowing latent images to be produced in minimal sunlight and then brought out by chemical means. It was probably thought impractical in such frigid conditions—the coldest climate on earth—to leave the wooden camera obscuras out for a full day.
Although Herschel’s hopes for photographic records of the expedition were dashed, the explorers were successful. Ross arrived at the Kerguelen Islands, an archipelago in the southern Indian Ocean, early in May 1840, in time to fulfill the plan made beforehand for simultaneous magnetic observations there and at all British and foreign observatories on May 29–30. The Terror’s assistant surgeon, the young Joseph Hooker—who would later go on to become one of the age’s foremost botanists, and a close friend of Charles Darwin—made important observations of the archipelago’s flora and collected specimens on the island. Ross was unable on this journey to reach the south magnetic pole; the ship got within 150 miles and then was stopped by impenetrable ice, but, using the Gaussian magnetic instruments suggested to the expedition by Herschel, Ross was able to compute the exact position of the pole to be 75°5’ south latitude and 151°45’ east longitude.
After sailing to Hobart, the ships set out on a five-month cruise within the Antarctic Ci
rcle. They met the hitherto unknown Great Ice Barrier (later named after Ross) and discovered Queen Victoria Land. Between 1842 and 1843, Ross charted part of the eastern coast of Graham Land, deep in the Weddell Sea, and then returned home via the South Shetlands and St. Helena.88 The south magnetic pole would not be physically reached until Douglas Mawson’s expedition in 1909.89
Meanwhile, Herschel and his fellow exponents of magnetic research were continuing in their attempts to persuade the government to fund the geomagnetic observatories. Having already spent £100,000 for the south polar expedition, the government was reluctant to commit more funds. Finally, in 1840, Herschel and Sabine were successful in obtaining government support for observatories in Greenwich, Dublin, Toronto, St. Helena, the Cape of Good Hope, and Van Diemen’s Land. The East India Company established observatories in Madras, Simla, Singapore, and Bombay. The Russian government agreed to establish ten observatories across its vast dominions, including one in Peking. Other cooperating observatories were erected as well, including those in Prague, Milan, Philadelphia, Cambridge (Massachusetts), Algiers, Breslau, Munich, Cadiz, Brussels, Cairo, Trivandrum, and Luknow. In all, fifty-three observatories were established throughout the world.90 As Whewell rather modestly put it (ignoring his own international tidal project), “Such a scheme, combining world-wide extent with the singleness of action of an individual mind, is hitherto without parallel.”91
In 1845, directly preceding the British Association meeting, which had returned to Cambridge, a “Magnetic Conference” was held to discuss the results of the observatories and the magnetic expedition. Both Whewell and Herschel worried that the magnetic crusade had resulted in mountains of observational data but little theoretical success.92 When all the data was finally analyzed years later, however, some important results emerged.
Sabine worked methodically on the data, publishing maps of variation, dip, and intensity in 1843 and 1844. He found discrepancies between what had been observed by Ross in the field and what had been predicted by Gauss’s theory of magnetism, which held that the earth’s magnetic field was determined purely by terrestrial forces. Later, in 1852, Sabine’s wife, Elizabeth, was translating Humboldt’s masterful work of natural philosophy, Kosmos, into English. Sabine saw that the third volume of this work discussed the newly reported results of Heinrich Schwabe’s seventeen-year study of sunspots, which had led him to conclude that there was a ten-year cycle of maximum sunspot activity. Sabine realized that there was a correlation between Schwabe’s observations and the timing of magnetic storms recorded at the colonial magnetic observatories. Further work on this relation—published by Sabine in 1868—led to the recognition that the earth’s magnetic field was determined, in part, by cosmic factors such as sunspots, thus disproving Gauss’s theory.93 This work also showed that William Herschel had been correct to suggest a connection between sunspots and atmospheric conditions on earth.94
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