Milestones Honor Maxwell's Equations and Franklin's Observations

Breakthroughs in electromagnetics and electricity are commemorated

6 August 2009

August is an electrifying month for IEEE. Two breakthroughs in electromagnetics and electricity are being commemorated with ceremonies recognizing them as IEEE Milestones in Electrical Engineering and Computing.

The first achievement, known as Maxwell’s equations, defined the field of electromagnetics. Physicist James Clerk Maxwell published the four equations in August 1865. Although they were based on the work of several physicists, the equations were named after Maxwell because of his key contribution: realizing that the equations—Gauss’s electric field law, Gauss’s magnetic field law, Faraday's law, and Ampère’s law—when taken together could completely describe the behavior of electric and magnetic fields. He rederived all four equations and, in doing so, reformulated Faraday's law and added a crucial correction to Ampère’s law. However, he published them in a different form than we know today, and alongside some other related but not central equations.

It was Oliver Heaviside who extracted the four key equations and put them in the form we know today. Immediately after this, Heinrich Hertz realized that the equations would lead to the existence of radio waves. The equations then became known as the Hertz-Heaviside or Heaviside-Maxwell equations. However, in the 20th century, Albert Einstein championed the primacy of Maxwell and referred to them as “Maxwell’s equations.” Given Einstein’s influence, that was the term that stuck.

Maxwell began researching electromagnetism in 1854 while a Fellow at Cambridge, but it was later, as a professor of natural philosophy at King’s College London, from 1860 to 1865, that he published two seminal papers on electromagnetic theory. In “On Physical Lines of Force,” in 1861, Maxwell made a crucial correction to Ampère’s circuital law. The law relates the integrated magnetic field around a closed loop to the electric current passing through the loop. Maxwell’s correction, adding an electric displacement current, enabled him to derive the electromagnetic wave equation. The equation, which describes the propagation of electromagnetic waves through a medium or in a vacuum, was featured in his 1865 paper “A Dynamical Theory of the Electromagnetic Field.”

The correction to Ampère’s circuital law also demonstrated a groundbreaking discovery: that light is an electromagnetic wave. In both papers, Maxwell pioneered the use of mathematics to describe the behavior of light. These papers led to his unified theory of electricity, magnetism, and light—electromagnetism. Maxwell summarized this theory in the four equations that bear his name.

THE FAB FOUR The first equation, Ampère’s circuital law, which includes Maxwell’s correction, has to do with what happens to electric fields when they change. For example, when static electricity from your finger arcs to the doorknob and shocks you, the electric field around your finger suddenly drops to zero. This sudden change generates a magnetic field.

Faraday’s law, the second equation, says the reverse is also true. If you change a magnetic field—by turning an electromagnet on and off, for example—you generate an electric field. The changing of electric and magnetic fields from one to the other results in electromagnetic radiation.

The third equation is Gauss’s law, which says static electricity must generate an electric field. You can see this in action when you shuffle across a carpet and get a shock when you touch a doorknob.

The last equation, known simply as Maxwell’s fourth equation, states that magnetic charge does not exist. The equation is still a mystery to physicists today.

Two Milestone ceremonies will be held to commemorate the publication of the equations. One will take place on 13 August at Glenlair House—Maxwell’s family home—in Kirkcudbrightshire, Scotland. The second will be held on 7 October at King’s College London. One plaque will be placed at Glenlair house, and another at the college. The plaques will be inscribed with Maxwell's equations and will inform visitors that between 1860 and 1871, at his home and at King’s College London, Maxwell developed his unified theory of electricity, magnetism, and light, summarized in the equations that bear his name.

ELECTRIC EXPERIMENTS In April 1751, the Royal Society, in London, published Benjamin Franklin’s book Experiments and Observations on Electricity, Made at Philadelphia in America. The collection of letters from Franklin to the London scientist Peter Collinson describes Franklin’s ideas about the nature of electricity and how electrical devices work, as well as his experiments to investigate lightning. The book led to a better understanding of electrical charge, earned Franklin the Royal Society’s highest award—the Copley Medal—and brought him international recognition. Now that book has earned Franklin another honor: an IEEE Milestone.

Franklin and members of the Library Company of Philadelphia—which he founded—conducted experiments on the nature of electricity from 1747 to 1751 throughout that city. Franklin drew on these experiments and observations to develop the first unifying theory of static electricity, lightning, and stored charge. Franklin observed that electricity is a substance that is conserved and that may be either positive or negative. To prove that electricity is a powerful and universal force of nature and that this force can be controlled, Franklin suggested an experiment, documented in the book, that was soon performed.

Franklin speculated that a sharp point could draw electricity from a thundercloud. After the book was published, Thomas-François Dalibard, in May 1752 in France, conducted Franklin's experiment using a 12-meter-tall iron rod, and he extracted electrical sparks from a cloud. The success of the experiment made Franklin famous as the man who showed how to get sparks from lightning. Also described in the book are “electrics”—now called dielectrics—such as glass and wax. The book also includes the law of conservation of charge, the first useful theory of the action of a condenser.

A ceremony commemorating the publication of Franklin’s volume will be held on 7 August at the American Philosophical Society Library, in Philadelphia. Franklin founded the society in 1743, and the library houses more than 300 000 volumes and bound periodicals, eight million manuscripts, 100 000 images, and thousands of hours of audiotape, all documenting the history of science, medicine, and technology.

A plaque will be mounted in the vestibule of the library describing the importance of the book in furthering the understanding of electricity. The ceremony will be held in conjunction with the 2009 IEEE History Conference, to be held 5–7 August, which will focus on the history of technical societies.

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