The Spinning Magnet

by Alanna Mitchell

  Thales of Miletus, who lived in the sixth century BCE, was in the sympathy camp. Known as the first Western philosopher, he was a gifted mathematician and astronomer who discovered the constellation Ursa Minor and correctly predicted the solar eclipse of May 28, 585 BCE. His ideas survive because Aristotle and others wrote about them. He’s credited with helping lay the foundation for the modern understanding of the world, resting on steely-eyed observation rather than dogma.

  For all his philosophy, Thales could be a practical man. Jeered at by wealthier neighbors in the Greek colony of Miletus on the coast of modern-day Turkey for living in poverty for the sake of his science, he played a sly joke. Figuring out one winter that the weather was shaping up to produce a good crop of olives the next fall, he raised enough money to rent every olive press at bargain prices. When the olives ripened, he rented out the presses at a handsome profit.

  His innovation, Aristotle tells us, was to say that magnets have souls, which is why they can make iron move. It was a bold rejection of the prevailing idea that only the gods could make things happen and a challenge to the worldview that substances and people were the pawns of the gods. Instead, understanding the world meant looking around you, then making theories and testing them—the basis of scientific experimentation. There is no record of whether Thales suffered punishment because of his ideas. Two clues suggest that he did not: He is reported to have died as an old man after collapsing at a gymnastics meet, rather than being imprisoned or shunned, and his school survived long enough to produce many other innovative philosophers.

  Empedocles of Acragas, a flamboyant Sicilian fond of wearing bronze slippers, who lived in the fifth century BCE, was in the opposite camp. He held that iron released physical effluvia, or vapors, from its “pores.” These vapors were drawn to the lodestone, dragging the iron helplessly in their wake. This physical explanation for magnetism hopscotched from one philosopher to another across the next several centuries, morphing slightly in each new iteration. In the fourth century BCE, Democritus was thinking about theoretical “atoms” that fitted together with balls and sockets or hooks and eyes. He said that bits of iron were drawn into lodestone, forcing the iron to connect to it. A century later, Epicurus attributed the magnetic force to a mysterious circular connection.

  Lucretius, the Roman who wrote De rerum natura (On the Nature of Things), in the first century BCE, was also in the mechanical bloc. His only known work is a 7,400-line poem composed in the dactylic hexameter that both Homer and Virgil popularized. It expanded on Democritus’s revolutionary idea of the atom. Lucretius contended that everything in the universe, including humans, is made of small bits—atoms. Not only that, but he said that the universe and its creatures have evolved over time. This went much further than Thales’s ideas. It was an outright rejection of the notion that the gods had created the world. Within this astonishing work, Lucretius described the lodestone as “the stone men wonder at,” as a Victorian translator put it. He said that air circulating between iron and lodestone created a vacuum, which drew the two together.

  Lucretius was lyrical if not comprehensive about the lodestone. And his work lay forgotten in just a few moldy handwritten manuscripts buried in European monasteries until it was rediscovered in the fifteenth century. Once again, it was incendiary. It would eventually influence some of the world’s most revolutionary modern scientific minds, including Galileo Galilei, Charles Darwin, and Albert Einstein.

  But for some of the early magnetic theorists, magnets did not have stories to tell about the planet’s birth or its future or the place of the gods. They were not ideologically controversial. Instead, magnets were curiosities or tools. Hippocrates, who founded Western medical thought in the fifth and fourth centuries BCE, said that bleeding could be staunched by binding a piece of magnetite—either whole or powdered—directly to the body. It was a natural progression from there to outright magic. By the fourth century CE, the author of the Orphic Lithica, a poem about the magical use of stones, wrote that magnetite could produce the pull of passion, whether human or divine. In other words, it was the longed-for key to desire.

  Its use as a navigational tool started early too. The Chinese appear to have begun developing intricate compasses using magnetite in the centuries before the common era. The Chinese called magnetite the “loving stone,” presumably for the same reason the French call magnets aimants, or “lovers.” In her book North Pole, South Pole, Gillian Turner, a physicist and historian of magnetism, describes the replica of an instrument likely used to help the Chinese lay out villages in harmonious directions. It featured a magnetite spoon symbolizing Thales’s Ursa Major constellation. The spoon rested on a bronze or wooden plate representing the heavens. Both the constellation and the heavens sat on a square plate, which was the Earth. The bowl of the spoon pointed north. Curiously, the Chinese appeared to use south as the primary reference direction rather than north.

  By the early twelfth century, Turner writes, the Chinese had become brilliant at making navigational compasses by stroking iron needles with magnetite, therefore forcing the iron needle’s unpaired electrons to line up temporarily in the same direction. They suspended the magnetized needles on silk threads or otherwise allowed them to point north-south, a feat not perfected in the Western world until decades later, when mariners began to rely on magnetized iron needles in their compasses. These seamen were known as “lodesmen.”

  But it was a medieval French engineer who was the father of modern magnetism, and some say, of modern scientific investigation. Pierre Pèlerin de Maricourt, also known as Petrus (Peter) Peregrinus, was a thirteenth-century scientist—possibly a knight—born in Picardy, the charmed region of northern France famous for its Champagne vines. There is no record of his early life, but he lives on in the annals of science for the 3,500-word letter he wrote to a friend on August 8, 1269, several copies of which survive. It is a treatise on magnetism written in Latin, the language of scholars and the upper class, and it contains results of some of the first experiments recorded in the history of science.

  Peregrinus seems to have been a tinkerer. He was certainly a builder of machines who may have studied at what was then the new University of Paris. The sobriquet “Peregrinus,” which literally means “a man who wanders” in Latin, signals that he was a crusader, a noble soldier fighting in one of a slew of the medieval era’s military campaigns to further the interests of the Catholic Church, sanctioned by whoever was pope at the time.

  Peregrinus wrote his letter while he was in the employ of Charles of Anjou, who was waging war against the mainly Muslim inhabitants of the hillside town of Lucera in Italy, a geopolitically important site in the Middle Ages. Charles, the brother of Louis IX of France, was one of the most ambitious of medieval European noblemen—and that was a rather high bar in those warlike times. Peregrinus was using his knowledge of warcraft to help with the prolonged siege, building fortifications around the French camp, laying mines, and overseeing siege engines such as catapults to lob missiles of fire and stone into the fortified city.

  Peregrinus obviously had some time on his hands, because there, in the shadow of war, he began thinking about the Greek mathematician Archimedes, who lived in the third century BCE and who was reputed to have made an ingenious, three-dimensional, Earth-centered model of the solar system, possibly in bronze. What if such a sphere could keep moving forever? Peregrinus wondered, imagining what today we would call a perpetual-motion machine, or dynamo. That’s when he began to muse about the magnet. You can almost picture him in the soldiers’ camp in the blistering heat of Italy’s August sun, distracted from war by the puzzles of the universe. And so he devised experiments to test the properties of the magnet.

  It’s hard, today, to reconcile this scientific urge with the society he lived in. Printed books did not exist. Paper was uncommon. Archives, including records from some of Charles’s other battles, were made on illuminated manuscripts created from painstakin
gly scraped sheepskin vellum. Brilliant reds on the manuscripts came from heating alchemical staples such as mercury or sulfur. Blues were from lapis lazuli, carried to Europe from the Middle East by camel and then ground into fine dust, fixed with egg or gum made from the boiled skin of a mammal. And while Greek and Roman architects and artists may have recognized linear perspective, by Peregrinus’s age, images were back to being two-dimensional. The knowledge of how toxic the art supplies could be was centuries in the future.

  Only about a dozen universities existed at that time anywhere in the world. The University of Paris, later called the Sorbonne, was barely more than a century old. The works of Aristotle and eventually Plato, long forgotten, were newly on the rise, part of a pulse of interest in education and culture that some scholars trace back to the first crusade in 1095. That crusade, and those that followed, introduced Europeans to the intellectual mysteries of the Greek and Islamic worlds, so when Latin translations of the ancient Greek philosophers began to appear for the first time, the best medieval minds pounced on them, parsing them intimately for insight into how the world worked.

  But at that time, science was philosophy, not observation; idea, not experimentation.

  The Bible was the most important book, the final word on the disciplines we now call physics, chemistry, geology, and biology. If the Bible said something, it was the word of God and therefore true. The official Vatican interpretation of the Bible was infallible, even if scientific observations seemed to contradict its interpretation. Peregrinus’s duty was to use science to bolster ideological belief.

  It was clear that Peregrinus knew he was onto something controversial. Most people of the day thought of magnetism as a fleeting magic: Sometimes it was there and sometimes it wasn’t. You couldn’t count on it. Or they saw it as a troubling, forbidden, quasi-sexual affinity that led one item to be drawn irresistibly to another, something that might not be able to be withstood or controlled, something that metaphorically represented the act of sexual congress itself, possibly the work of the devil. The idea that magnetism could be a fundamental phenomenon of the universe could not have been further from the public mind.

  “The disclosing of the hidden properties of this stone is like the art of the sculptor by which he brings figures and seals into existence,” Peregrinus wrote to his friend. “Although I may call the matters about which you inquire evident and of inestimable value, they are considered by common folk to be illusions and mere creations of the imagination.”

  What hidden properties? Peregrinus was the first to figure out that a magnet has two poles. He was one of the few early investigators to note that a magnet repels as well as attracts. But to Peregrinus, the idea of poles did not contain the idea of movement, or of a field. He couldn’t have imagined unpaired spinning electrons in an atomic array. His explanation was that the magnet carried within itself a replica of the heavens, by which he meant the stars that point to geographic poles, aligning with the axis of the planet. They’re called sailors’ stars because sailors have used them to navigate for hundreds of years and occasionally do so today.

  Peregrinus gave his friend instructions on how to find a lodestone’s poles, the results of his astonishing experiments. During what was presumably a quiet time at the siege of Lucera in the summer of 1269, he writes that he first placed the lodestone in a small round wooden bowl, then placed that bowl in a large vessel so full of water that the small one floated. The north pole of the stone steered the small bowl toward the north pole of the heavens, and the south pole of the stone to the south pole. “Even if the stone be moved a thousand times away from its position, it will return thereto a thousand times, as by natural instinct.”

  Schoolchildren have now for generations conducted experiments similar to Peregrinus’s. They rub a needle vigorously across a magnet, which aligns the unpaired electrons in the needle’s iron content temporarily with the magnet’s poles, and then they place the needle on a cork or a bar of soap in a bowl of water. The needle’s north will then align with what we call magnetic north, and the south with the south.

  The details of where and how Peregrinus conducted his experiments have not survived. But there are a few clues to set the scene. During the Second World War, British aerial reconnaissance photographs of that part of Italy revealed buried sites likely from Charles’s siege of Lucera and from much earlier Roman and Neolithic settlements. Subsequent archeological excavations unearthed evidence of a substantial medieval military camp outside the walls of the besieged town. Pottery found there from that period includes large glazed dishes with ringed bases painted green, yellow, or brown; often featuring a lively painted figure at the center, usually a mammal, bird, fish, or human; likely large enough in which to float a small wooden bowl containing a lodestone. Illuminated manuscripts describing Charles’s military actions at this time depict men with chins meticulously shaved, hair cut in a fringe high on the forehead, falling to below the chin and then cut across the top of the shoulder in an unswerving line. In battle, their heads and necks were protected by a cowl of fine chain mail. Helmets were rounded. The most noble of the men, likely including Peregrinus, wore mid-calf-length garments dyed in brilliant solid colors, girded with a leather belt, sword slung at the hip. Crossbows were in common use. Soldiers who could not afford swords or crossbows showed up with spades and pickaxes. Military engagements in the thirteenth century were primarily affairs of the cavalry, so horses were a feature of the camps and therefore so were farriers and smiths. How did Peregrinus manage to steal away to his scientific endeavors amid the cacophony and odor of a camp such as this?

  Shortly before Peregrinus finished his magnetic letter in 1269, Charles of Anjou, tired of waiting for more than a year for the inhabitants of Lucera to succumb, cut off their food supplies, making sure that a thirty-mile radius around the town was devoid of animals and other foodstuffs. Less than a month before Peregrinus wrote his letter, Charles, who had already instituted a thorough conscription, stepped up his reserves, ordering in five hundred lances for men on horseback and another five hundred for those on foot. He hired one hundred carpenters, plus brick makers and wall builders, and laid in hemp, rope, chamois leather, and iron and grindstones to sharpen the weapons. By the time Peregrinus finished his letter on August 8, the inhabitants of Lucera were reduced to eating grass. They surrendered before the end of that month, starved into submission. Three thousand were slain. Charles boasted that they had prostrated themselves on the ground before he had them slaughtered.

  Peregrinus mentions none of this drama. Maybe he was hunkered down in the mess tent by wooden bowls and water vessels, but, alas, those details are lost.

  We do know Peregrinus didn’t stop with the easiest experiments. He discovered that even if you cut the lodestone in half or in progressively smaller pieces, each piece was a new magnet with the same two poles. It would have been more logical to think that if you cut a magnet in half, one pole would remain in the first half and the second pole in the second half. But not so. And it didn’t matter how small you cut the magnet; each piece still had two poles.

  His experiments also showed that north poles attracted south ones and repulsed other norths. South attracted north and shied away from south. This was revolutionary stuff. Then he used his findings to create an early version of the round compass, a magnetized needle surrounded by a circle divided into 360 degrees. It could be used to describe where one was in the world.

  But while all those discoveries were shocking and new, Peregrinus’s greatest finding was that the lodestone carried what he called natural instinct. That meant that the lodestone’s powers were not ephemeral but constant, and, in Peregrinus’s understanding, irrevocably linked to the power of the stars. He was still a long way from being able to peer inside the Earth and understand the forces that create magnetism or—more revolutionary still—posit that those forces could reverse the direction of the magnetic flow, but his was the first effort to establish th
at magnetic power surrounds us all, invisible and inescapable.

  CHAPTER 5

  revolutions on paper

  When Kornprobst was a graduate student at the Sorbonne in Paris in the late 1950s, his professors used to save their highest ridicule for two theories: that the continents drift and that the magnetic poles reverse. Today, Kornprobst said, craning his neck to point up a hill behind a Citroën car dealership in the town of Boisséjour near Clermont-Ferrand, both are geological gospel.

  The hill was the site of another piece of the Brunhes puzzle. Shortly after assuming the directorship of the observatory in Clermont-Ferrand, Brunhes had read three key scientific papers that had launched his quest to understand more about magnetism. Like other scientists of his generation, he knew that the magnetic field was shifty. It was thought to be composed of three parts: declination, inclination, and strength. (Today, they are compressed into direction and strength, but declination is still noted on any high-quality map.) Any point on the planet could be described by those three magnetic coordinates. It was more complex than the typical two-dimensional geographic mapping coordinates of latitude and longitude. The problem was, magnetic coordinates changed slightly over time.

  Declination is straightforward. Compasses point home to the magnetic pole along magnetic lines of force that converge at the poles. But beginning in the eleventh century, the Chinese scientist Shen Kuo realized that the spot the compass points to is different from the Earth’s geographical pole. The geographic North Pole, for example, can be found directly underneath the North Star. Shen wrote about this in his 1088 chronicle Meng Chhi Pi Than (Dream Pool Essays). By the early fifteenth century, European mariners knew this too. The angle of difference between the geographic pole and the magnetic line of force is known as declination. By convention, if you are east of geographic north, your declination is positive; west is negative. Declination changes depending on where you are on Earth. It also changes if you stay put but measure it over time. Not only do the magnetic poles themselves shift around, but the magnetic field lines that the compass responds to do too. It’s counterintuitive, especially if you’ve done those magnetic experiments with iron filings shaken onto a piece of white paper laid over a bar magnet. The filings arrange themselves with spooky precision along the magnet’s lines of force, intersecting at the poles. But the Earth’s field lines are not tidy like the ones on the white paper. They are stretchy and prone to wild distortions. Over decades, those changes could be dramatic. For example, modern reconstructions show that declination in London in 1653 was positive. By 1669, it was negative. After gyrating greatly in the ensuing years, by 2018 it looks headed to become positive again.