by Nancy Forbes
Published 2014 by Prometheus Books
Faraday, Maxwell, and the Electromagnetic Field: How Two Men Revolutionized Physics. Copyright © 2014 by Nancy Forbes and Basil Mahon. All rights reserved. No part of this publication may be reproduced, stored in a retrieval system, or transmitted in any form or by any means, digital, electronic, mechanical, photocopying, recording, or otherwise, or conveyed via the Internet or a website without prior written permission of the publisher, except in the case of brief quotations embodied in critical articles and reviews.
Cover image of Michael Faraday (top) used with permission from the Royal Institution, London, UK/The Bridgeman Art Library
Cover image of James Clerk Maxwell (bottom) courtesy of the Master and Fellows of Trinity College, Cambridge
Jacket design by Jacqueline Nasso Cooke
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The Library of Congress has cataloged the printed edition as follows:
Forbes, Nancy, author.
Faraday, Maxwell, and the electromagnetic field : how two men revolutionized physics / by Nancy Forbes and Basil Mahon.
pages cm
Includes bibliographical references and index.
ISBN 978-1-61614-942-0 (hardback)
ISBN 978-1-61614-943-7 (ebook)
1. Faraday, Michael, 1791-1867. 2. Maxwell, James Clerk, 1831-1879. 3. Electromagnetic fields. 4. Physics. I. Mahon, Basil, author. II. Title.
QC16.F2F67 2014
537--dc23
2013039969
Printed in the United States of America
Acknowledgments
Chronology: Principal Events in the Story of the Electromagnetic Field
Introduction
1. The Apprentice: 1791–1813
2. Chemistry: 1813–1820
3. History: 1600–1820
4. A Circular Force: 1820–1831
5. Induction: 1831–1840
6. A Shadow of a Speculation: 1840–1857
7. Faraday's Last Years: 1857–1867
8. What's the Go o’ That? 1831–1850
9. Society and Drill: 1850–1854
10. An Imaginary Fluid: 1854–1856
11. No Jokes Are Understood Here: 1856–1860
12. The Speed of Light: 1860–1863
13. Great Guns: 1863–1865
14. Country Life: 1865–1871
15. The Cavendish: 1871–1879
16. The Maxwellians: 1850–1890
17. A New Epoch: 1890 Onward
Notes
Bibliography
Index
The seeds for this book were sown over thirty years ago when one of us was a graduate student in physics and heard a lecture by Nobel laureate C. N. Yang about the role of symmetry in twentieth-century physics. Yang spoke of the birth of a pristine and heretofore unheard-of concept born from the simple instruments found in Michael Faraday's laboratory in the Royal Institution: field theory. It was the rise of this idea that gave way to most of the major developments in modern physics and became the basis for today's reigning theory of matter and forces, the Standard Model. Yet Faraday's work, by itself, could not have had the monumental effect on physics it had without the subsequent efforts by Scottish physicist James Clerk Maxwell to put Faraday's idea into mathematical language, which resulted in a full-fledged theory of the electromagnetic field. Yang, who made his own fundamental contributions to field theory, truly understood how radical and how profound this new concept was.
It was a story that was begging to be told. Many people lent a hand in getting this book written. Correspondence with Faraday scholars Frank James and Ryan Tweney helped to clarify aspects of Faraday's work. Talks with Maxwell biographer Francis Everitt also added to the narrative. Discussions with friends such as Tony Fainberg, Phil Schewe, Allan Blaer, Will Happer, Freeman Dyson, Mal Ruderman, Barbara and Jeffrey Mandula, Louise Marlowe, Robert and Linda Avila, and Simki Kuznick helped to fine-tune the story and make the physics more accessible. Thanks to Lee Bartrop for his carefully drawn diagrams throughout the text, as well as to John Bilsland for the diagrams of Maxwell's spinning cells model. Thanks also to Tom Haggarty at the Bridgeman Art Library for making available many of the images found in the photo insert. Trinity College Library at Cambridge University also gave us permission to reproduce several Maxwell images. Our editor at Prometheus Books, Steven L. Mitchell, recognized the importance of our story early on and has handled our queries with patience and graciousness.
We are grateful for permission from the publishers of two of Basil Mahon's earlier books to include short extracts: to John Wiley and Sons for the diagram and accompanying text describing Maxwell's spinning cells model in The Man Who Changed Everything: The Life of James Clerk Maxwell (2003), and to the Institution of Engineering and Technology for the descriptions of the electromagnetic power vector and the curl and divergence operators in Oliver Heaviside: Maverick Mastermind of Electricity (2009).
1600 William Gilbert publishes De Magnete and proposes that Earth acts as a giant magnet.
1687 Isaac Newton publishes Principia Mathematica.
1733 Charles du Fay distinguishes between vitreous and resinous electricity.
1745 Pieter van Musschenbroek and Ewald von Kleist independently invent the Leyden jar, a device that stores electricity.
1747 Benjamin Franklin puts forward the idea of positive and negative electric charge.
1750 John Michell demonstrates the inverse-square law of magnetism.
1766 Joseph Priestley demonstrates the inverse-square law of electricity.
1785 Charles Augustin Coulomb carries out precise experiments to confirm the inverse-square laws of electricity and magnetism.
1800 Alessandro Volta invents the voltaic pile, or battery, thereby making it possible to generate continuous electric currents.
1820 Hans Christian Oersted shows that an electric current in a wire deflects a compass needle.
1820 André Marie Ampère begins to formulate a combined theory of electricity and magnetism based on action at a distance.
1821 Michael Faraday discovers the principle of the electric motor.
1825 François Arago shows that a compass needle rotates when suspended over a spinning copper disc.
1831 Faraday begins to compile his Experimental Researches in Electricity.
Faraday discovers electromagnetic induction and the principle of the dynamo.
Faraday introduces the concept of lines of magnetic force.
1832–1833 Faraday discovers the basic laws of electrolysis.
1845 Faraday introduces the term magnetic field.
Faraday shows that a strong magnetic field rotates the plane of polarization of light.
1846 Faraday gives his “Ray-vibrations” talk at the Royal Institution.
Faraday discovers diamagnetism and shows that all substances have magnetic properties.
1855–1856 James Clerk Maxwell publishes his paper “On Faraday's Lines of Force.”
1861–1862 Maxwell publishes his paper “On Physical Lines of Force.”
1864–1865 Maxwell publishes his paper “A Dynamical Theory of the Electromagnetic Field.”
1873 Maxwell publishes his Treatise on Electricity and Magnetism.
1882 Oliver Heaviside and Josiah Willard Gibbs independently propose vector analysis and vector notation.
1885 Heaviside summarizes Maxwell's theory of elec
tromagnetism in the four now-famous “Maxwell's equations.”
John Henry Poynting and Heaviside independently derive the formula for energy flow in an electromagnetic field.
1887 Abraham Michelson and Edward Morley attempt to measure the aether drift but instead demonstrate that the speed of light is independent of the motion of the observer.
1888 Heinrich Hertz produces and detects electromagnetic waves in free space.
1892 Hendrik Lorentz publishes his theory of the (then-hypothetical) electron.
1897 Joseph John Thomson discovers the electron.
1900 Max Planck proposes the quantum to explain the black-body radiation spectrum.
1901 Guglielmo Marconi sends a telegraph signal across the Atlantic Ocean.
1905 Albert Einstein explains how quanta produce the photoelectric effect and predicts the photon.
Albert Einstein publishes his special theory of relativity.
It is 1888. Picture a large, sparsely furnished room. It has stout wooden tables and workbenches—a laboratory of some kind—but there are no retorts, Bunsen burners, or flasks of brightly colored liquid. Instead, the room is stocked with curious metal devices that have strange names: Rhümkorff coils, Knochenhauer spirals, Wheatstone bridges.1 Their purpose is to probe the ways of the mysterious invisible phenomenon—electricity.
The room has a single occupant, a young man, handsome, neatly suited, and dark-haired with a close-trimmed beard and moustache. He is deftly assembling some apparatus on one of the long wooden tables. At one end he has constructed a circuit that will produce electric sparks across a narrow air gap between two metal spheres connected to the ends of the wires in the circuit. Ordinarily air doesn't conduct electricity but, if the two spheres are close together and the voltage is high enough, a spark will appear to jump across the gap, although it is really a series of very rapid sparks that jump back and forth, or oscillate, between the spheres. To each sphere he has attached a metal rod connected to a rectangular metal plate—he has learned that this will alter the frequency of oscillation. He presses a key to activate the circuit, and vivid blue sparks crackle across the gap between the spheres.
So far, so good; his primary circuit works, as it had the day before and the day before that. He turns his attention to a separate part of the apparatus that he calls his detector—a simple loop of wire with a very small gap between its ends that he can adjust with a screw. He holds the detector close to the sparking primary circuit, and faint sparks appear across its own gap. This happens, he reasons, when waves of energy pass from the primary circuit to the detector.
All this is familiar ground to him, but the next steps are untried and will, he hopes, be decisive ones. Switching off the primary circuit for the moment, he props up a large zinc sheet in a vertical position at the far end of the table. Its purpose is to act as a reflector, like a mirror. He places the detector on the table between the primary circuit and the zinc reflecting sheet, closes the blinds, waits for his eyes to adjust to the darkness, and then switches on his primary circuit. Turning his back on the sparks scintillating between the spheres, he looks for tiny sparks between the terminals of his detector. They appear, faint but unmistakable. Now for the step that will, if successful, establish the result he is seeking. He looks to see if the brightness of the sparks varies as he moves the detector slowly away from the primary circuit toward the reflecting zinc sheet. Indeed, it does. The sparks diminish to nothing, then grow again to their brightest, and then the cycle repeats. He knows that when any kind of wave is reflected back toward its source, it forms a standing wave, which appears to vibrate in place, like a guitar string. Hence, waves are being produced by the primary circuit and reflected by the zinc sheet. This is exactly what he wanted to find. Heinrich Hertz, professor of experimental physics at the Technische Hochschule in Karlsruhe, has made one of the greatest experimental discoveries in the history of science: he has proved beyond doubt the existence of electromagnetic waves.
As Guglielmo Marconi and others were soon to show, the commercial value of Hertz's discovery was immense. But he had no notion of this, nor, indeed, of any practical application. What had captivated Hertz and set him on his quest was a beguiling but strange scientific idea—the brainchild of British experimentalist Michael Faraday in the 1830s that had been raised into a full mathematical theory by the young Scot James Clerk Maxwell three decades later. Their idea was so different from anything that had gone before that many of the leading men of the time dismissed it as a flight of fancy. Others were simply baffled; they did not know what to make of it. But to Hertz it was a beautiful idea that rang true. All it lacked was physical proof, and his quest was to supply experimental evidence that would put the matter beyond dispute.
From the time of Newton, leading scientists had believed that the universe was governed by mechanical laws: material objects held energy and inflicted forces. To them, the surrounding space was nothing more than a passive backdrop. The extraordinary idea put forward by Faraday and Maxwell was that space itself acted as a repository of energy and a transmitter of forces: it was home to something that pervades the physical world yet was inexplicable in Newtonian terms—the electromagnetic field.
Faraday's first notion of lines of force, much derided at the time, grew into Maxwell's sophisticated mathematical theory, which predicted that every time a magnet jiggled, or an electric current was turned on or off, a wave of electromagnetic energy would spread out into space like a ripple on a pond, changing the nature of space itself. Maxwell calculated the speed of the waves from the elementary properties of electricity and magnetism, and it turned out to be the very speed at which light had been measured. He surmised that visible light is just a small band in a vast spectrum of electromagnetic waves, all traveling at the same speed but with wavelengths that might range from nanometers to kilometers. All this remained just a theory with more skeptics than adherents until a quarter of a century later, when Hertz emphatically verified it by producing and detecting what we would now call shortwave radio waves in his laboratory. The door to previously unimaginable regions of scientific knowledge was opened.
It is almost impossible to overstate the scale of Faraday and Maxwell's achievement in bringing the concept of the electromagnetic field into human thought. It united electricity, magnetism, and light into a single, compact theory; changed our way of life by bringing us radio, television, radar, satellite navigation, and mobile phones; inspired Einstein's special theory of relativity; and introduced the idea of field equations, which became the standard form used by today's physicists to model what goes on in the vastness of space and inside atoms.
Faraday and Maxwell have attracted their share of biographers, and rightly so. Aside from their genius, both were admirable, generous-spirited men who conducted their science with infectious enthusiasm and exuded the kind of charm that made people feel better about themselves and the world in general. But perhaps even more compelling than their individual life stories is the way that the two men from totally different backgrounds—a self-taught son of a poor blacksmith and a Cambridge-educated son of a Scottish laird—were brought together by their curiosity about the physical world and their determination to find out how it works. Although they met only late in Faraday's life, they formed a tremendously strong bond—they were united by their willingness to challenge entrenched scientific customs and conventions. The theory of the electromagnetic field is their joint creation and has its own story, intertwined with theirs and with its own set of diverse supporting characters. There were, for example, the American rake Count Rumford, who was instrumental in founding the Royal Institution, which gave employment to the impecunious, young Faraday; the brilliant but vain Humphry Davy, who was Faraday's inspiring mentor; the maverick Oliver Heaviside, who summarized Maxwell's theory into the four famous “Maxwell's equations”; and the hardworking Oliver Lodge, who discovered waves along wires but found he had been comprehensively scooped by Hertz.
Welcome to the story of th
e electromagnetic field.
There are many places where one could begin this story. Perhaps the best is the rugged moorland on the windswept western side of the Pennines in the north of England. This was the kind of country depicted by Emily Brontë in Wuthering Heights, sparsely populated by hardy souls who eked out a living in a land where crops barely grew and sheep had to search hard to find sustenance. It was home to Michael Faraday's forbears.
The Faradays had joined a small sect of Christians that came to be called the Sandemanians, after Robert Sandeman, a Scot who had broken from the Presbyterian Church of Scotland and come to England in the mid-1700s. The Sandemanians worked hard, lived simply, and spoke plainly. Rejecting all the trappings of the established churches, they held to the simplest possible form of Christianity—their whole doctrine was contained in the epitaph on Sandeman's tombstone: “The bare death of Jesus Christ, without a thought or deed on the part of man is sufficient to present the chief of sinners spotless before God.”1 Though friendly to outsiders and tolerant of those with different views, they largely kept to their own society. This didn't stop them doing business: Faraday's father, James, was a blacksmith, and among his uncles were a weaver, a grocer, an innkeeper, and a tailor.
The life of Michael Faraday might have begun and passed quietly in the remote seclusion of rural Westmorland but for the pressure of wider events. In the mid to late 1700s, Britain had been fighting rival colonial powers at sea for many years, and it finally lost an expensive war against its own colonists in America. The cost of these ventures had taken its toll at home, and a looming revolution in France held the prospect of a new cross-Channel war. Meanwhile, the Industrial Revolution was drawing people from the English countryside to the towns and cities: farmworkers left the land for the ironworks, potteries, and textile mills. Against this background, trade in Westmorland fell, but James Faraday, newly married, had his wife, Margaret, to support and wanted to start a family. In 1786, he decided to leave his ailing smithy in Outhgill and try his luck in London.