The Paramore arrived home on September 10, 1700, to Deptford, almost a year to the day after its last departure. If anyone had expected royal fireworks, they would have been disappointed. There weren’t even any special notices in the London newspapers. Halley’s final entry in his ship’s log was perfunctory: “We delivered our guns and gunners stores and the pilot being on board by low water we weighed from Long Reach and delivered the pink this evening into the hands of Captain William Wright, Master of Attendance at Deptford.”

Halley soon arrived in London. The odd bounty he carried, gleaned from nearly two years and many thousands of undulating miles, was a clutch of numbers. Never had anyone shown as much interest in the wide blue sea—not merely the shoreline—and brought back little else but abstract data. These nearly 150 observations ranged from roughly 50 degrees north latitude to 50 degrees or so south latitude. He hoped they would be translatable into something worthy of the expense. If the readings seemed less immediately impressive than

a haul of gold or spices, Halley needed more time and hunched over his data to prove otherwise. Even to the thinkers at the Royal Society, it was not yet evident what Halley had accomplished.

By February 1701, after months of work, Halley issued his best results. As many ways as there were to stare at the numbers and coordinates, no new overarching theory of magnetism emerged. He would not be able to publish a tidy equation for magnetism as Newton had done for gravity. But in connecting the dots, the plots of similar declination values, patterns had emerged. Halley had converted his daily observations into curved lines depicting areas of equal magnetic variation. Looking a bit like an alien spider web, the chart showed for the first time the invisible magnetic field that swaddled Earth—or at least some of its features.

If hardly earth-shattering to those scientists who were hoping for a new theory, Halley’s results were immediately useful to sailors and to the large practical world of trade. (And the findings did nothing to upset his earlier theory.) He proudly and boldly made his curved lines as prominent as those of latitude and longitude. Although the execution may have appeared confusing at first, the chart superimposed the invisible (yet real) magnetic lines over the artificial common grid of mariners. And in this one step he boosted the utility of the grid, increasing the probability of finding one’s way, at any point along the way, within this global latticework.

In a sense, if a map shows you how to find your way, this was a “metamap,” one that reduced your chances of getting lost. Halley probably anticipated that most sailors would find the chart intimidating. The usually modest man felt the need to call out its novelties. “What is here properly new, is the Curved-Lines drawn over the several seas, to show the degrees of the variation of the magnetical needle, or sea compass,” Halley wrote in a description in the top corner of his chart (see Appendix). “They’re designed according to what I myself found in the Western and Southern oceans in a voyage I purposely made at the public charge in year of our Lord 1700.”

Halley called them “curved lines.” Soon they came to be called

“Halleyan lines.” To this day they remain the leading method for delineating this information (though we now call them isogonic lines, a more encompassing term that would come into use a century after Halley’s mission).

His 1701 magnetic sea chart debuted to immediate success. The course of Halley’s journey aboard the Paramore was etched into a single 22- × 20-inch sheet. It was the first printed and published map to employ isolines to indicate a specific value of a particular measurement, in this case magnetic declination. John Harris did the engraving. His chart went on sale at the Postern on Tower Hill by a recently launched partnership of Richard Mount and Thomas Page.

This was the culmination of his career and involved a wealth of skills. And Halley played it as far as he could. The chart also traced Halley’s voyage into iceberg-infested waters, visits to exotic territories, and stops at St. Helena, Rio de Janeiro, Bermuda, and Newfoundland. Pictures hinted at his encounters with new species. Halley made no mention of his escapades with Lieutenant Harrison, however.

Halley was so proud of his enhancement of the Mercator representations that he thought it should be given a special name. “The Projection of this Chart is what is commonly called Mercator’s; but from its particular Use in Navigation, ought rather to be nam’d the Nautical; as being the only True and Sufficient Chart for the Sea.” But in this case, his proposed name didn’t catch on enough to displace the 16th-century innovation of Flemish geographer Gerardus Mercator.

Time would prove that Mercator’s projection, which purposefully distorts the pattern of latitude and longitude lines to always cross at right angles, would in fact best represent magnetic field declination on navigational charts. On such maps the distances between parallels of latitude generally increase from the equator toward the poles proportionately with spacing of longitude meridians. Rhumb lines, or lines of constant compass bearing that ships typically steer along appear as straight lines. The major disadvantage of this type of projection is that polar regions appear especially enlarged.

This combination of new English isolines overlaid on the old Flemish projection became popular across Western Europe. His chart was commonly pasted in editions of the English Pilot and became a best-seller. There was no Battle of the Books regarding its utility. People recognized the fact that it made compass navigation more accurate and the world a little less mysterious. It was almost as if all sea pilots, formerly nearsighted, suddenly viewed the world in crisper detail. Paths at sea from now on would be more efficient and approaches to shorelines safer.

Halley’s achievements, the charts, were praised in his lifetime. On Halley’s return, Dr. John Wallis, Savilian Professor of Geometry at Oxford and a long-time member of the Royal Society, wrote that his

Halley dedicated that first chart, which covered the Atlantic (mistakenly judged the world’s largest ocean by Wallis), to King William III.

The king never remarried after Queen Mary’s death in 1694. Although during her lifetime he had an ongoing affair with one of her

ladies-in-waiting, Elizabeth Villiers, it was more of a ploy to win Mary’s devotion. Despite the rough start of their arranged marriage, Mary, who was 12 years his junior, came to love him and his native Holland. His lasting grief after her death, however, revealed his true feelings of respect and admiration for her and explains his dedication to fulfilling her ambitions for England.

Fortunately for Halley, William rewarded him with a handsome bonus for his contribution just before his death in March 1702. The 200-pound authorization was equivalent to 12 years of wages for the average able-bodied sailor.

Since Halley’s day and the dawn of global exploration, charting the changing Earth’s surface field has been essential to world powers. Even almost two centuries later, for instance, Halley’s charts were touted by G. Hellmann, a prominent German historian of science, as “a masterpiece of practical navigation.” His representative system was embraced as being “of the greatest importance in all branches of physical geography.”

Contour-type lines of equal field increments are still plotted today. And the science of determining one’s continual geolocation within a grid has continued to make astounding leaps of accuracy—from high-tech military targeting to car navigation.

As William Gilbert had recognized at the time of Shakespeare, Earth itself acted as a giant magnet. Now, a century later, Halley had become part of that history. By trekking much of the aqueous globe, he had created a unique treasure map to share with anyone who wanted it.

GILBERT DIDN’T PUBLISH his textbook on geomagnetism until 1600. Ostensibly, among the first science books aimed at the public, the text attempted to separate myth from fact:

Iron’s magnetic properties and its relative abundance on the planet had lent credence to Gilbert’s original idea that Earth was a permanent magnet. Yet one of Gilbert’s more important contributions was the notion of spherical influence, which would in turn spur Kepler to develop his laws of planetary motion and eventually describe a magnetic field. Kepler was among the first to consider that Earth’s gravity and the Sun’s gravity might somehow be “magnetic,” though his ideas were somewhat wrongheaded.

The first Royal Astronomer Flamsteed, too, suggested magnetism might produce gravity, the nature of which would remain very much a mystery for some time. But his explanation of how was also off base. Newton only scratched the surface of geomagnetism in his Principia. He gave it little thought and simply noted it was likely “very small and unknown.”

In the second half of the 17th century, Royal Society pioneer Robert Boyle advocated the idea that magnetism was caused by a corporeal, atomic effluvium that was in constant movement. (Effluvium was a pet theoretical device.) His improvement of the air pump helped confirm that magnetic action occurs in a vacuum. Boyle argued that direct contact with an effluvium caused magnetic attraction—an idea that was compatible with Gilbert’s permanent magnet hypothesis.

A general belief emerged among English thinkers that variation in magnetic properties occurred because of changes in the iron’s texture due to mechanical operations. The concept supported Boyle’s notion of effluvium. To pursue this line of inquiry, the Royal Society created a “Magnetics Committee,” which compiled declination measurements and conducted various lodestone experiments. Annual

measurements of variation were made in London by other investigators as well.

Years before Halley’s mission, faith in magnetic philosophy as an independent discipline was replaced by the notion that magnetism would be explained under the rubric of effluvial dynamics, essentially the movement of an invisible vapor comprised of the smallest but still tangible component of an element. This conclusion relegated magnetism back into the broader category of study—that of what would later be known as terrestrialism. Halley and others turned their attention toward deciphering the inner workings of the planet.

Despite decades of supposition, a leading question remained: how to explain the slow but sure motion of the lines of magnetic declination by a couple minutes or so of arc each year. Descartes, for one, supposed that iron ore deposits on the Earth’s surface might account for the motion. But Halley had debunked such a notion during his 1676 trip to St. Helena. Other ideas, such as Robert Hooke’s that the magnetic poles were moving in extremely slow circles several degrees off kilter from the geographic poles, also didn’t hold up.

In his 1683 paper Halley suggested that “the whole Globe of the Earth is one great Magnet, having 4 Magnetical Poles or points of Attraction … and that in those parts of the world which lie near adjacent to any of those magnetical poles, the needle is governed thereby; the nearest pole being always predominant over the more remote.”

His idea was that there were two north magnetic poles and two south magnetic poles. In a follow-up paper in 1692, he surmised that one of each must be on the Earth’s surface. And the second pair must be located on an inner sphere, perhaps 500 miles beneath the surface.

When he presented his first paper on geomagnetism to the Royal Society, Halley ran an experiment for the society using a needle and two lodestones. He demonstrated that a compass needle follows the closest and strongest magnetic source. He divided the Earth into four imaginary regions, each ruled by a distinct magnetic pole. He proposed that the fourth was significantly stronger than the others, which

added a layer of complexity. The poles were placed such that they were unbalanced enough that two separate antipodal dipoles would not result.

The setup would account for the variations in declination that he and others observed. If the inner and outer spheres rotate at different speeds, he reasoned, the changes would occur. Halley thought so highly of his theory that his portrait, painted at age 80, had a diagram of his spherical shells in the foreground.

In his day, Halley’s initial paper on geomagnetism drew the ire of his one-time mentor Flamsteed. He believed Halley had borrowed key ideas from a little-known mathematician named Peter Perkins, whom Halley consulted on his deathbed in 1680. Perkins was master of a prestigious school for boys, the Royal Mathematical School at Christ’s Hospital, established to produce a small cadre of highly trained navigators. Originally a hospital for friars, Christ’s Hospital was converted to a charity school in the 16th century, and by the time of Perkin’s arrival it had become London’s largest school.

Flamsteed alleged: “His discourse in the former transactions concerning the variation of the needle and the 4 poles it respects I’m more than suspicious was got from Mr. Perkins…. He was very busy upon it when he died…. Mr. Halley was frequently with him and had wrought himself into an intimacy with Mr. Perkins before his death, and never discussed any thing of his 4 poles till sometime after I found it published in the transactions.”

Halley never admitted any wrongdoing, let alone did he bother to defend himself. He let Flamsteed stew over his alleged “art of filching from other people and making his works their own.” The dispute marked the beginning of the decline in their relationship. No one of renown substantiated Flamsteed’s charges. It is known that Perkins was working on his own theory of variation, but there’s no evidence it was similar to the one Halley presented.

At minimum, their clash over Perkins’s data reveals an apparent difference in their worldviews. Flamsteed had a sense of proprietorship when it came to his research and demanded that his data only be

disclosed at his discretion. Scholars attribute his attitude in part to his penchant for perfectionism. He didn’t want to publish data prematurely that might still be enhanced. Prone to taking on large issues, Halley believed in essence in the value of sharing data and that the data of public servants, even if underpaid, belonged in the public domain. He actively sought out the results of others to develop hypotheses about not only geophysical but also historical patterns. Halley’s method typically entailed compiling observations from varied sources and then publishing them openly in the Philosophical Transactions.

Flamsteed was relentless in his campaign against Halley. In a November 1686 letter to Richard Towneley, a colleague of Boyle’s and fellow researcher known for his work on air pressure and safekeeping of Gascoigne’s micrometer, he opined:

Hooke, incidentally, had long grown tired of Flamsteed as well. After all, a decade before Flamsteed had branded him “a conceited cockscomb.” Hooke had returned such salvos in kind, considering Flamsteed “proud and conceited of nothing” and an “ignorant impudent ass.” And in more recent diary entries, Hooke—not once but twice—flat out wrote: “Flamsteed mad.” Whether he thought Flamsteed insanely angry or a bit nuts remains open to interpretation.

In many areas of emerging science the fringe is often not far from the facts. Astronomers acknowledge their debts to astrologers, chem-

ists to alchemists. Recall that even Newton pursued alchemy, and he continued to do so even after writing the Principia. Boyle was likewise fascinated with alchemy and corresponded with Newton on the subject. Over the centuries, the charms of magnetism attracted charlatans, as well as bona fide scientists like Halley, with remarkable consistency. Magnetics have been linked to everything from water witching (using a divining rod to locate underground water sources or metal deposits) to health remedies to the cause of shipwrecks in the Bermuda Triangle.

Petros Peregrinus, a French scholar and experimenter, wrote the first detailed descriptions of both floating and pivoted compasses in his 1269 Epistolia de Magnete, which was also the first western account. Peregrinus was convinced that a lodestone could be manufactured that would serve as an impeccable timepiece if it could just be properly cut and positioned. Shortly thereafter others proposed that a mechanical clock could be constructed to keep perfect time at sea and obsolete the astrolobe, a celestial planisphere that is rotated over a plate that divides the heavens into a network of bearings, or azimuths, and altitudes, or almacantars, according to the vantage point of an observer at a given altitude.

In the early 16th century, some, like Spain’s Gemma Frisius of Louvain, believed clock technology had advanced enough to be carried at sea. When the notion reached England, the self-taught seaman William Borough tested the reigning watch technology. But such watches lost as much as 15 minutes a day and required seemingly constant winding. After less than a month at sea, that margin of clock error could translate to an error in longitude as large as an ocean. A successful timepiece needed to be accurate within seconds for several weeks at sea.

Robert Hooke was among the first to recognize that a pendulum-based chronometer would not work at sea. While Huygens was perfecting his pendulum clock at the French Academie, Hooke was toying around at Oxford with spring-driven marine chronometers that didn’t rely on pendulums to set a clock’s pace. Huygens, however,

beat him to a patent on a similar spring balance clock in France in 1675. Hooke was somehow insulted while trying to patent his device in England. Henry Oldenburg, still a Royal Society secretary, cast one of the barbs, backing Huygens’s prototype over Hooke’s. Hooke abandoned the patent, precluding even a preliminary trial. Oddly enough, Hooke didn’t appreciate the importance of the capability of determining longitude at sea. “No kind or state would pay a farthing for it,” he declared.

While an eternal clock that worked at sea would for a time prove quite valuable to society, the concept of a perpetual motion machine powered by magnetism, first proposed by the very same Petros Peregrinus, would become a perpetual lark in the science world. In the 18th century, one true believer presented his ideas for a perpetual motion machine not once but twice to the Royal Society. He argued that it would run best in Barbados at the magnetic equator. There the intense horizontal component of the field would continually flip a bar magnet. The U.S. Patent and Trade Office continued to grant patents for perpetual motion machines well into the 1970s. To date, none has been built, but a few enthusiasts still hold out hope.

Peregrinus also proposed a magnetic levitation device. Jonathan Swift lost no time parodying supporters of the idea in Gulliver’s Travels, first published in 1726. Once again taking a shot at the natural philosophers, Swift described a flying magnetic island he called Laputa that hovered over fictitious lands. He suggested that magnetic repulsion could act as “anti-gravity,” suspending the island in space. Swift also wrote of Laputa’s astronomers who calculated the periods of 90-odd comets. Again he was taking a satirical swipe at Halley, the return of whose comet 32 years later would naturally quell such ridicule.

A more personal use of magnetism developed shortly after Halley’s death, when Franz Anton Mesmer, a Viennese physician, introduced magnetic remedies to the field of medicine. He claimed he could manipulate the magnetic fields that he believed ran through all living creatures. Although he enjoyed famous clients like Mozart,

when Mesmer moved his practice to Paris, Louis XVI set up a royal commission in 1784 to look into this so-called animal magnetism. Written by the likes of Antoine Lavoisier, Benjamin Franklin, and Joseph Guillotin, the commission’s report found that “animal magnetism may exist without being useful, but it cannot be useful if it does not exist.” A series of controlled experiments revealed that Mesmer’s art was nothing more than the power of suggestion. Nonetheless, the word “mesmerize” was added into the vernacular of many western countries, and his ideas would influence the development of hypnosis and chiropractics in the United States.

A late-18th-century magnetic quack, Dr. James Graham, encouraged upper-class newlyweds in London to spend their wedding night in a suite filled with tons of magnets with the promise of conceiving “super children.” After his initial success, Graham’s “Royal Patagonian Magnetic Bed” was found to be fraudulent.

Claims, which have continued to resurface over the course of recent centuries, that magnets offer health benefits have lost ground under modern scrutiny. Today, hucksters still advertise them to provide pain relief, but such remedies have yet to pass clinical muster.

Perhaps because he was just too busy, Halley, unlike his friend Newton, resisted prolonged departures into abstract mysteries. But Halley’s theoretical quests often yielded practical ends.

ALTHOUGH HIS THEORY of geomagnetism never panned out as he intended, his chart offered a navigational tool for sea captains. Such was the demand—avant-garde mariners wanted to correct their compasses—that Halley began to expand the chart to cover more of the world. To make it more legible, Halley created a better explanation of the chart to accompany it.

In a marvelous display of scientific sharing of data, Halley, using data supplied by many others, expanded his famous chart in 1702 into Halley’s World Chart of Magnetic Variations, “A New and Correct Sea Chart of the Whole World showing the Variations of the Compass as they were found in the Year MDCC.” Despite its all-

encompassing title, though, it wasn’t entirely global—not enough reliable information existed to cover the Pacific—not to mention that on it California appeared as an island. The expanded chart was dedicated to Queen Anne’s consort: “Prince George of Denmark, Lord High Admiral of England, Generalissimo of all Her Majesty’s Forces.”

Halley couldn’t resist a parting gibe in the Battle of the Books saga. His new patron was Queen Anne, sister of his original patron, Queen Mary. In a Latin ode to Her Majesty on his world map, he contrasted the esteemed empires of Greek and Roman antiquity to that of modern Britain. Its Latin verses, translated, read:

He also praised the unknown inventor of the compass or nautical box:

These long-gone verses were printed on charts for mariners and carried across oceans until the turn of the next century. At the time of its early publication, Halley had encouraged additional contributions to improve his chart. “All knowing mariners are desired to lend their assistance and information, towards the perfecting of this Useful Work. And if by undoubted Observations it be found in any part defective, the Notes of it will be received with all grateful Acknowledgement, and the Chart Corrected accordingly.”

The later charts apparently also included data from other seamen. It was a consummate display of international scientific process: collaborative data gathering, with results open to criticism and ready to be amended by future improvement.

From existing copies of various editions, historians note that it was reprinted frequently with minor changes. No doubt the wider dissemination of information through increased trade helped advance science and navigation, including many of Halley’s contributions. The utter volume of reprints and revisions seems to indicate the charts were unquestionably a practical success. But the constantly changing magnetic field of Earth also pushed revisions.

Whenever supporting evidence was presented to Halley or the Royal Society, he updated the charts. Other researchers frequently submitted new data, as evidenced by the steady stream of reports in the society’s correspondence. But wide calls for data from other mariners were only heeded now and again. In a 1714 paper, written a year after he was honored by election to secretary of the Royal Society and assumed control of the Philosophical Transactions, which heralded its Newtonian era, Halley mentioned some recent observations of mag-

netic variation in part of South America by the French. In the same paper he also documented the naming of the Falkland Islands by a Captain Strong, who came across them while searching the South Seas for the hull plate from a wreck.

Printers in France and the Netherlands also published Halley’s world chart. Around 1740 the Dutch East India Company adopted the Halley charts for its ships with the intent to use them to estimate longitude from the variation.

The need for accurate variation charts would continue for some time, and Halley’s trend-setting isogonic charts would continue to be updated into the 19th century. To steer a ship properly, the helmsman required corrected courses derived from the chart. The continual shifting of the Earth’s magnetic variation, however, rendered the ever-popular maps almost obsolete as soon as they were published, likely reducing their practical value, some scholars purport.

For determining longitude, Halley’s method did not work for the most part. It proved useful for locations where the isogonic lines run parallel to a coast, such as that of southern Africa (at least at that period in time until the Earth’s field shifted again). Halley was well aware of the shortcomings of his approach. It was impractical in most locations. Moreover, he knew that the points where it did work were temporal. “There is a perpetual, tho’ slow Change in the Variation almost everywhere, which will make it necessary in time to alter the whole system,” he acknowledged.

Halley’s work confirmed the concept of secular or temporal variation, which he had observed as a schoolboy in 1672 and written about in 1683. His ideas on the subject expanded on Henry Gellibrand’s 1635 discovery that magnetic declination changes with time.

“There is yet a further difficulty,” Halley wrote, “which is the change of the variation, one of the discoveries of the last Century; which shows that it will require some Hundreds of years to establish a complete doctrine of the Magnetical system.” With such a timeline in

mind, Halley was clearly not expecting a revolutionary theory to emerge right after his Paramore mission.

Even after Halley published his charts that added to his luster, Flamsteed still held a grudge. Pursuing an ongoing investigation of Halley’s 1683 submission to the Royal Society, Flamsteed asserted in a 1702 letter to Christopher Wren that, “I have some papers in my hands that prove him guilty of disingenuous practices.”

The dispute remains unresolved by today’s historians. Yet to many, Halley’s 1692 paper on geomagnetism, which was clearly his own, rendered Flamsteed’s charges irrelevant. It fleshed out his hypothesis of the detailed structure of Earth’s interior. Very likely its analytical bent was strongly influenced by the style of Newton’s Principia. In the second paper, Halley actually applied the physical limits spelled out by Newton to his postulate.

Regardless of the origin of some of the ideas in his first paper on geomagnetism, Halley’s mission aboard the Paramore significantly contributed to what we now know as geophysics—more so than his basic meteorological chart and other previous innovations.

And Halley prospered in good company. Not only geophysics, but many scholarly disciplines we still recognize today were seeded in this period. For example, the roots of taxonomy can be traced to this time when methods for classifying animals and plants were first hotly debated. The work of John Ray, dubbed by Anglophiles the English Aristotle, was especially influential in establishing a classification system. Meanwhile, practicing as a physician, Hans Sloane, still secretary of the Royal Society, was well on his way to establishing himself as a great collector and cataloger of the living world, his eclectic natural treasures to form the basis of the British Museum. Profound insights about today’s world can indeed be gained from Halley’s.

In London in 1724 George Graham, although primarily an instrument maker, noticed that the compass needle every now and then veered off at a small angle for maybe a day or two. The effect was not only local. At the same time in Uppsala, the Swede Anders Celsius observed the same thing. A century later the effect was found to be

worldwide, and Alexander von Humboldt would call such events magnetic storms.

Throughout this period, experimenters were really aware of only the existence of permanent magnetism, the type exhibited by magnetized iron or lodestones. On the surface the magnetic force due to the magnetic pole at the end of a magnet seemed a bit like gravity (or an electric force), which decreased in proportion to the inverse square of the distance from the pole. In 1777 in France, Charles Coulomb confirmed this inverse square relationship by experimenting with a magnetic needle suspended on a twistable spring. Magnetic detectors would be based on this instrument, which Coulomb invented, for almost two centuries.

Basic tenets of Halley’s magnetic hypothesis would resurface over the next centuries, and later researchers would propose ideas similar to his. Christopher Hansteen, for one, a Norwegian physicist and astronomer who led an expedition to Siberia to study geomagnetism, put forth a four-pole theory in the early 19th century. And even a leading contemporary theory about Earth’s magnetic field suggests, like Halley’s, that the solid inner core might rotate at a different rate than outer regions. However, knowing that the Earth is not a permanent magnet, the theorists proposed an entirely novel process. (This notion was debunked when scientists recognized that materials lose their magnetic properties at high temperatures. The Curie temperature, as it came to be called, is about 770 degrees Celsius for iron.)

It would be more than a century after Halley’s death when German mathematician and astronomer Karl Friedrich Gauss introduced improved techniques for observing and analyzing Earth’s magnetic field. For example, in 1832 he devised the magnetometer, essentially a permanent magnet suspended horizontally by a gold wire, to measure the strength and direction of magnetic fields. In 1840, Gauss improved the technique by attaching a mirror to the suspended compass magnet. This enabled the angular motion of the compass to be accurately detected from a distance when a light source was bounced off the mirror and tracked. Another century would pass after that

before Sidney Chapman and Julius Bartels would move the field into the modern age.

But in June 1701 the Paramore still had another mission in her. Halley wasn’t prepared to relinquish his command just yet, and the monarchy was willing to oblige him one more time.