What Did James Clerk Maxwell Discover? The Man Who Showed That Light Is Electromagnetism

James Clerk Maxwell (1831–1879) discovered that electricity, magnetism and light are all parts of one phenomenon. His equations showed that changing electric and magnetic fields can travel through space as waves, and when he calculated the speed of those waves, it came out at almost exactly the speed of light. From this he proposed that light itself is an electromagnetic wave, an idea that has since been amply confirmed and that underlies radio, television, Wi-Fi and mobile phones. Along the way he also showed that Saturn's rings are made of countless small particles, produced the first durable colour photograph and helped found the physics of gases.

"Daftie" from Edinburgh

Maxwell was born on 13 June 1831 at 14 India Street in Edinburgh; the house is now a museum. Much of his childhood was spent at Glenlair, the family's country estate in south-west Scotland.

When he arrived at Edinburgh Academy at the age of ten, he did not fit in. His homemade shoes, his odd tunic and his rural Galloway accent earned him the nickname "Daftie" from the other boys. The boy they mocked was anything but daft. At 14 he wrote his first scientific paper, about drawing oval curves with a loop of string, and it was presented to the Royal Society of Edinburgh by a professor, because Maxwell himself was considered too young to present it.

Cambridge and a professorship at 25

After the University of Edinburgh, where he discovered photoelasticity by experimenting with blocks of gelatine, Maxwell went to Cambridge in 1850. He graduated in 1854 as Second Wrangler, the second-best mathematics student of his year, and shared the prestigious Smith's Prize.

In 1856 he became Professor of Natural Philosophy at Marischal College in Aberdeen, and in 1858 he married Katherine Mary Dewar there.

What are Saturn's rings made of?

In Aberdeen Maxwell tackled a famous prize question: what are Saturn's rings actually made of? Seen through a telescope they look like smooth, solid bands, but appearances can deceive. Using careful mathematics rather than a better telescope, Maxwell showed that the rings must be made of numerous small particles, and the work won the Adams Prize in 1859. It is a lovely example of his style: answering a question about something billions of kilometres away with pen and paper.

The first colour photograph

Maxwell was fascinated by how we see colour. The idea behind colour photography is that many of the colours we see can be built up by mixing red, green and blue light. In 1861, during a lecture at the Royal Institution in London, he gave the first demonstration of durable colour photography, using an image of a tartan ribbon photographed by Thomas Sutton. The screen of the device you are reading this on still uses the same red-green-blue principle.

Light is an electromagnetic wave

Maxwell's greatest work was done at King's College London in the early 1860s. His aim was to describe electric and magnetic forces with precise mathematics. In "On Physical Lines of Force", published in 1861 and 1862, he built a model of electric and magnetic fields.

His key addition was the idea that a changing electric field produces a magnetic field, just as Faraday had shown that a changing magnetic field produces an electric field. Maxwell called this new term the "displacement current". Put the two together and something remarkable happens: a changing electric field creates a changing magnetic field, which creates a changing electric field, and so on. The disturbance can sustain itself and travel through empty space as a wave.

Around 1862 Maxwell worked out how fast such a wave would move. The answer was approximately the measured speed of light. That could hardly be a coincidence. In his 1865 paper "A Dynamical Theory of the Electromagnetic Field", he proposed that light is itself an electromagnetic disturbance. At a stroke, optics and electromagnetism became one science.

Maxwell's equations in plain words

Maxwell set out his complete theory in A Treatise on Electricity and Magnetism in 1873. The compact modern form that students learn today is credited to Oliver Heaviside. Without any symbols, the four equations say:

• Electric charges create electric fields that point away from positive charges and towards negative ones.
• There are no isolated magnetic "charges"; every magnet has both a north and a south pole.
• A changing magnetic field creates an electric field, which is how generators produce electricity.
• Electric currents and changing electric fields create magnetic fields.

Four short statements, and from them come radio, radar, microwave ovens, electric motors and the light of the stars.

Gases, demons and a famous laboratory

Maxwell did not stop at electromagnetism. Between 1859 and 1866 he developed a statistical description of how fast the molecules of a gas move, now known as the Maxwell–Boltzmann distribution. In 1867 he invented "Maxwell's demon", a thought experiment about a tiny being sorting fast and slow molecules, which still fuels debates about heat and information. His 1868 paper "On governors", about the kind of speed regulators used on engines, laid the theoretical basis of control engineering.

In 1871 he became the first Cavendish Professor of Physics at Cambridge and oversaw the building of the Cavendish Laboratory, which would become one of the most famous physics laboratories in the world.

An early death and a lasting epoch

Maxwell died in Cambridge on 5 November 1879, aged just 48, of abdominal cancer, the same illness that had killed his mother at the same age. He did not live to see the full triumph of his ideas.

Albert Einstein later said that "one scientific epoch ended and another began" with Maxwell. In a survey of 100 leading physicists by Physics World, Maxwell was ranked third of all time, behind only Newton and Einstein. Not bad for the boy they called "Daftie".

Learn with Maxwell: English phrases about connecting ideas

Phrase	Meaning	Example
to connect the dots	to see how separate facts fit together	After a year of study, I started to connect the dots.
two sides of the same coin	two things that are closely linked	Reading and writing are two sides of the same coin.
on the same wavelength	thinking in the same way	My tutor and I are on the same wavelength.
it's no coincidence	it happened for a real reason	It's no coincidence that I improved after daily practice.
ahead of his time	having ideas too modern for his era	Maxwell was ahead of his time.

Try this: Maxwell saw that electricity, magnetism and light were connected. Write three English sentences about two skills in your language learning that are "two sides of the same coin", using "connect the dots" and "it's no coincidence".