The revelation for scientists in the late eighteenth and early nineteenth centuries was that they could make electricity flow. At that time, they believed that electricity was a fluid that ran through wires and so they called it “current” electricity, as if it were a running river. Today, we say that electrical current is the one that moves from the socket through the wires into your lamp. What makes that happen? The electromagnetic field can be harnessed to push electrons through substances known as conductors and make them travel from one place to another. The human body is a conductor. Others include metals that have at least one unpaired electron in an outermost filled orbital, like copper, which is often used in electrical wiring. The old incandescent bulbs used to have a metallic tungsten strip in them where the electrons collected and heated up the metal, producing heat and light. New LED bulbs, like the ones in the art display at the Niels Bohr Institute, shine because electrons are forced into shedding some of their energy in the form of tiny units of light called photons, which are extremely short electromagnetic waves.
A key to all of this is that while the electromagnetic force is fundamental to the universe and will live as long as the universe, the process for harnessing that force into making a current is only about two hundred years old. And forcing immense amounts of current into a vast, interconnected transmission system, like the modern electrical infrastructure we rely on, is only about one hundred years old. As a society, we devote significant amounts of time, thought, and money into keeping these systems going. But as the planet’s magnetic field undergoes its restless contortions inside the Earth’s core, the transmission systems themselves are put at the kind of risk no one imagined when they were created. Under certain circumstances that scientists are just beginning to track, the planet’s human-built electrical transmission system could be switched off.
CHAPTER 12
jars full of lightning
While the bid to understand magnetism was an impassioned quest over centuries, fraught with theological risks and potentially stupendous financial rewards, the study of electricity was, by contrast, slack-twisted until the middle of the eighteenth century. Even then, electricity did not question the position of the planets or the sun or the age of the Earth. It did not endow the planet with its own soul or try to wrest the Bible from its perch of authority. It was “cosmologically neutral.”
Early philosophers, including the same canny Thales of Miletus who cornered the ancient Greek market in olive presses and looked at the power of the magnet, also examined electricity. Thales is said to be the first to realize that if you rubbed amber, which is a honey-colored fossilized tree resin, it could attract pieces of chaff—a phenomenon he noticed because Greek women of the seventh century BCE occasionally spun wool with precious amber spindles. Some of those spindles can still be found in museum collections today.
But to the ancients and most medieval researchers, electrical draws were, seemingly, even more impermanent than the pull of the lodestone. Under certain circumstances, if you rubbed amber, it created sparks, but not always. Occasionally, pieces of feather or chaff would temporarily stick to the rubbed surface of amber. But damp or rainy days scotched any deliberate attempt to make sparks or attract chaff. The sparks and the sticking chaff are static electricity, the result of electrons being shaken free from their orbitals, producing slight electric charges and temporarily lodging in other orbitals. When a material such as amber is damp or the air surrounding it is, the water acts as a conductor for the electrons, ferrying them away and preventing them from building up into a spark. In the minds of the early researchers, electricity was not a key to understanding the universe. It was a mildly interesting, fleeting, largely inscrutable curiosity. There was certainly no electric crusade.
It took William Gilbert, intemperate physician to England’s Elizabeth I, to show a sustained experimental interest in electricity. As he was doing research for his treatise De Magnete, published in 1600, in which he explained his shocking conclusion that the Earth’s magnetic power rested deep inside its core, he also looked at amber. He discovered that not only amber but also a range of other substances, including jet and diamond, could be made to attract chaff when they were rubbed. He named the phenomenon “electricity” and then dismissed it as inferior to magnetism, the grand force that he believed, wrongly, kept the Earth in its daily and yearly rotation.
Even Isaac Newton, the towering Enlightenment physicist who, in 1687, published his mathematical description of gravity, one of the other four fundamental forces of the universe, didn’t get very far with static electricity. It fascinated him, though. He ran numerous experiments in the late seventeenth century to try to understand it. In a note on December 7, 1675, to the new Royal Society of London for Improving Natural Knowledge (now simply the Royal Society), he described in confusing detail how to make very thin triangular bits of paper dance underneath a round piece of glass rubbed and set overtop a brass ring. The instructions failed. The fellows of the society wrote back to him asking for further directions and finally got the show to work using stiff boar bristles to rub the glass.
As the modern American historian of science J. L. Heilbron explains, Newton’s note is remarkable for demonstrating how little even the most accomplished natural philosophers of the day knew about electricity. Even the era’s most eminent mathematician could make neither heads nor tails of why static electricity crackled and danced.
A series of experiments begun in 1733 by Charles François de Cisternay du Fay, the wealthy scion of a French military family, was the first systematic attempt to compile findings on electricity from all over Europe. Up until then, the experiments showed scattered, inconsistent results. Du Fay wanted to put things in order. He wanted rules.
His first finding was that everything, except fluids and things too soft to rub, could be made electrical by friction, or excitation, as he called it. It means every substance can produce static electricity if you rub it the right way and if it is dry. And how did that electrical “virtue,” or static electricity, get transferred to other substances? Both by touch and by proximity, du Fay discovered. But he added a large caveat: The substance receiving the electrical spark had to be laid on something that did not conduct electricity—an antielectric or insulator. This became known as the rule of du Fay and was followed assiduously for more than a decade.
Du Fay’s experiments also convinced him that there are two types of static electricity. We would say that there are positive and negative charges, like the balloon you rub on your hair that is negatively charged because it has picked up electrons and your hair that is positive because it has lost them. But du Fay came to believe, wrongly, that certain substances could have either one type of electricity or the other, but not both.
By the middle of the eighteenth century, electricity was no longer the poor relation of scientific technology. It had come into its own. Two discoveries made all the difference. The first, discovered independently by at least two experimenters, and named after a Dutch university town, was the first condenser, also known as a capacitor, which temporarily stored static electricity in a glass jar. The second was by the American diplomat and scientist Benjamin Franklin, who fished for electricity in the skies with his kite.
Researchers into electricity, who called themselves “electricians,” not only began to catch a glimpse of a future where electricity might be made to do things, but now they also knew that it was somehow linked to the majestic drama of the stormy skies. “Forty years ago, when one knew nothing about electricity but its simplest effects, when it was regarded as an unimportant property of a few substances, who would have believed that it could have any connection with one of the greatest and most considerable phenomena in Nature, thunder and lightning?” said Samuel Klingenstierna, a professor of physics at Uppsala University in Sweden in 1755.
The first big advance came in the 1740s. For years, experimentalists had been able to produce shocks of static electricity th
rough friction, following du Fay’s findings. They experimented with making stronger and stronger shocks. While some of the electricians believed that they knew everything there was to know about electricity and that there was no need for further research, others wondered whether electricity was a fluid that they might be able to imprison and transport in a jar. Many of the electricians’ contemporaries considered the goal ludicrous, as absurd as boxing a light beam inside a soap bubble, as a later historian of electricity put it.
But then in January 1746, the legendary Dutch physicist Pieter van Musschenbroek, a professor of philosophy at the University of Leyden who had turned down royal sums to teach several of Europe’s science-hungry kings, made a breakthrough. He was repeating an experiment made by a lawyer who was an amateur scientist and who had been fiddling around in van Musschenbroek’s laboratory. This amateur didn’t know about the rule of du Fay that insisted that the substance to be charged up had to be set on an insulating material. So he held a water-filled jar in his hand, electrified it with static electricity, touched the wire carrying the charge, and got a spark.
Two days later, van Musschenbroek repeated the experiment. He hooked a thin glass globe to a metal gun barrel suspended by silk threads. One assistant used a contraption to turn the globe rapidly while another steadied it, sending the electrical charge down the length of the gun barrel. Attached to the end of the gun barrel was a brass wire, which entered a jar partly filled with water. Van Musschenbroek held the jar in his right hand and then tried to draw sparks from the wire with his left. The immense voltage of the static electrical force jumped into his right hand. His whole body shook as if hit by lightning.
The charged electrons created by friction between the globe and the gunmetal rushed across the unpaired electrons of the metal and the brass wire and collected inside the glass, trapped there by the fact that the glass could not conduct the electrons further. The wire became one half of an electrode, and van Musschenbroek’s highly conductive hand became the other. Each half of the pair was equally charged until van Musschenbroek touched the wire with his other hand and the charges from the wire rushed to their opposites in van Musschenbroek, carrying immense voltage. The process carried the risk of electrocution, and in fact the instrument, which became known as the Leyden jar after the city where van Musschenbroek lived, was used experimentally to kill animals.
Van Musschenbroek wrote up the experiment in Latin in a letter to the French scientist René Antoine Ferchault de Réaumur. He was still trembling with fear: “I wish to inform you of a new, but terrible experiment, which I advise you on no account to personally attempt,” he wrote, adding that he wouldn’t repeat the dreadful thing even if he were to be given the whole kingdom of France. “In a word, I believed I was done for,” he wrote.
More important, van Musschenbroek didn’t understand what he had done. The experiment had defied the rule of du Fay because there was no insulating material under the glass globe. It made no sense to him. “I’ve found out so much about electricity that I’ve reached the point where I understand nothing and can explain nothing,” he wrote to Réaumur.
The Leyden jar was a revelation, both for science and for high-society entertainment. Future scientific refinements replaced the jar’s water with a lead lining, inside and out, creating the two sides of the electrode. And as long as one didn’t inadvertently touch the wire going in with anything that could conduct the electrical charge, the electricity could stay inside the jar for hours or even a few days and be released later. Not only that, but the “electricians” soon realized that they could connect one Leyden jar to another and one more again in order to make the shock bigger. It was like a rather cumbersome, short-life prototype battery, differing from modern batteries in that the electricity came from friction rather than chemical reaction.
The jars transfixed the eighteenth-century Enlightenment establishment. As the Cambridge University historian of science Patricia Fara explains, making electricity became an international obsession. All of a sudden, people felt that they could control the spark of life. They had power. It was intoxicating.
It was also dangerous. Citizens and researchers who tried replicating van Musschenbroek’s experiments or who offered themselves as subjects to be experimented on reported nosebleeds, passing paralysis, weakness, and dizziness, the result of what today we recognize as high-voltage shock. “I found great Convulsions by it in my Body,” wrote the Leipzig classics professor Johann Winkler. “It put my Blood into great Agitation; so that I was afraid of an ardent Fever; and was obliged to use refrigerating Medicines. I felt a Heaviness in my Head, as if I had a Stone lying upon it. It gave me twice a Bleeding at my Nose, to which I am not inclined.”
Still, a conundrum presented itself. Was the electricity—or fire—that men and women could make by friction the same as that made by nature? Lightning, for example, seemed similar to the sparks produced from the Leyden jar. But was it? Or were they two utterly separate entities? The American businessman, intellectual, and scientist Benjamin Franklin set himself the task of finding out.
Franklin is best known today for his role in helping to draft the American Declaration of Independence, his diplomatic efforts on behalf of the British colony of Pennsylvania, and his many inventions, including the stove that still bears his name. But he was also an internationally celebrated, self-taught “electrician” who devised ingenious experiments and made seminal findings throughout his long life. He was awarded the Copley Medal in 1753—the highest scientific award of his day and the equivalent of today’s Nobel Prize—“on account of his curious Experiments and Observations on Electricity.”
He became fascinated with electricity in 1745, when an American scientist friend sent him a glass wand for experiments from London and breathlessly revealed in a letter that all Europe was agog at parlor-room demonstrations of the new electrical charges. Truly, his friend wrote, they were living in an “age of wonders.” Franklin enthusiastically taught himself to perform the demonstrations in his home before throngs of visitors, and then taught them to a neighbor, whom he encouraged to hit the lecture circuit with the electrical oddities. It smacked of a carnival, judging from quotes Fara cites from posters advertising the neighbor’s lectures. “A curious Machine acting by means of the Electric Fire, and playing [a] Variety of Tunes on eight musical Bells,” reads one. “A Battery of eleven Guns discharged by a Spark, after it has passed through ten Foot [sic] of Water,” reads another.
For Franklin, electricity was far more than an entertainment. He ran a spate of careful experiments to explore what it could do. At one point, he methodically disassembled the Leyden jar to discern which part of it held the electrical charge or “virtue,” as Joseph Priestley, the eighteenth-century theologian, scientist, educator, and historian of electricity explained. (It was the glass, which served as the insulator.) Like du Fay, Franklin also determined that everything is inherently electric and that electricity has both negatives and positives that have the urge to balance out. He said that substances can be forced to go out of balance so they will have a charge to give off. He also asserted that electrical charge can be neither created nor destroyed; it can only move around. These were remarkably astute observations that hold up today, even if Franklin and du Fay could not express them in terms of moving electrons. The same spirit of logical deduction based on observation led the naturalist Charles Darwin to figure out several decades later that species evolved and adapted to their environments, even before Gregor Johann Mendel published his findings about genes, serving up a fundamental insight into the mechanism for how life forms have changed.
And then there was lightning, the experiment Franklin is most remembered for. It was not as random as it has sometimes been depicted, but rather the stepwise continuation of electrical research he had been conducting for years. His aim was to determine whether lightning was the same thing as the electricity that gathered in the Leyden jar from friction. So, on a stormy day
in Philadelphia in June 1752, he made a kite with a silk sail, a wooden spine and spar, plus a strong bridle. To the spine, he attached a wire. To the end of the kite’s hemp line, he attached a metal key wrapped in silk, which in turn was attached to a Leyden jar. Lightning lit up the sky, some electrical charge hit the wire (not likely a full strike of lightning, which would have killed him), ran through the line, passed through the key, and filled the Leyden jar. It was indistinguishable from any other electrical spark that the jar had contained. Franklin had drawn fire from the heavens and shown that it was the same as the human-made spark. He was jubilant.
The physics of lightning is still being explored today. But at base, lightning is a long spark of static electricity. As hail, ice, and super-cooled water droplets bang around within a storm cloud, they shake loose electrons. The electrons gather around low-hanging hail, creating a negative mass toward the bottom of the clouds. The positively charged ice crystals move up toward the top of the clouds. When the negative charge builds up enough, a long line of static electricity cracks toward the Earth or toward another cloud, searching for a positive charge. As the electricity moves, its heat makes the air flash with light and expand abruptly, causing the sight of lightning and the sound of thunder.
The Spinning Magnet Page 10
