Within physics he is placed in the same category as Einstein or Newton. Yet he is often an unknown name to the outside world:James Clerk Maxwell. He took crucial steps in understanding electricity, magnetism and light. Possibly his brave character was the reason for his relatively limited fame. The brilliant Scot turned out to be very enthusiastic to speak to Kennislink.
A bright lightning in the sky and you immediately realize that electricity is one of the most impressive forces in nature. For a long time people did not know exactly what electricity is. Thanks in large part to the Scotsman James Clerk Maxwell (1831 – 1879) we now know. In mathematical equations he established that electricity, magnetism and light are all expressions of the same thing:an electromagnetic field. The fact that we can no longer imagine a world without electricity today is largely due to him.
Less well known is that he also achieved success in other areas, such as color vision, the workings of gases and Saturn's rings. He also made the very first color photograph and was a virtuoso poet. Maxwell was a beloved man, with a warm and engaging personality. Kennislink did a 'fictional interview' with the mathematician and physicist.
Mr Clerk Maxwell, nice to talk to you. Did you know that you are by far the youngest age of the physicists we speak to for our Handsome Heads series? “Well, thank you for the invitation. I feel honored. Apparently my work has had the necessary impact, because I have not experienced it that way myself. I suspect that my work on electromagnetism will open up new areas, but I can't foresee what consequences this will have for science.”
We know your equations about electromagnetism - which we'll talk about in detail in a moment - as the Maxwell equations, but they were almost called the 'Clerk equations', weren't they? “That's right, my father's name was originally John Clerk. However, he turned out to be heir to a plot of land in the Middlebie area of southwestern Scotland. The area had belonged to the Maxwell family and a condition of taking over the land was that he take the name Maxwell. Hence, he changed his name to John Clerk Maxwell. That's how I got those two surnames."
You spent much of your childhood in Middlebie. Was it a pleasant place to grow up? “Yes, my parents had a small but cozy house – Glenlair House – built in the town of Glenlair. We had a farm in the middle of a large piece of land. There was so much to see and discover. I was very curious from childhood.
I wanted to know how each device worked. ‘Show me how it box! ’ I shouted. And my father was always willing to explain that. I also loved animals, especially with our dogs I built a close bond."
Your talent for mathematics showed itself in primary school, the Edinburgh Academy. How did you experience school? “In the beginning it took some getting used to. I started a month after the start of the school year, so the groups were already formed. A group of bullies called me 'Dafty ’ (Scottish for ‘dummy’ or ‘dumb’, ed.), because I wore my farm clothes and had a strange accent in their eyes. Oh well, I could laugh about it, I didn't care. It did mean that I was quite lonely at school at first, but later I became good friends with Peter Guthrie Tait and Lewis Campbell.
I didn't find the classes at school that exciting. It wasn't until my senior year, the fifth, that it got fun. We were taught geometry and I found that highly interesting. I became fascinated with the way you can draw ellipses, with a pen that spins on two pinned strings. I explored more complex ways of drawing ellipses and described their mathematics. When my father saw my work, he immediately showed it to Professor James Forbes of the University of Edinburgh, he found it so impressive. What happened according to Forbes? I had done similar work as René Descartes (the famous French philosopher, ed.) in the seventeenth century. They thought that was very clever for a fifteen-year-old boy."
In a way, this was the beginning of your professional career. A career you continued in Edinburgh, and later Cambridge. Your interest in colors and how we perceive them began during your studies. How did that happen? “As a child I was already fascinated by colors. I was once taken by my Uncle John to William Nicol's lab. He made prisms with which you could polarize light. This had an effect on what colors you saw. Fascinating! I was therefore pleasantly surprised when James (Forbes, ed.) asked me in 1849 to participate in experiments on seeing colors.
We worked with discs on which you can place pieces of colored paper. If you turn the disc you can see what color those pieces give each other. For example, we tried to investigate with which color combinations you could make gray or white. Later, after graduating from Cambridge, I continued the experiments. Only now I looked at how you can make other colors from the combination of green, blue and red."
So just like the Englishman Thomas Young had done before? “Indeed, he and Helmholtz developed a theory that our eyes see colors as a mixture of primary colors:red, green, and blue. I designed a kind of color viewing box with which you could adjust the amount of red, green or blue light. This allowed me to measure people's sensitivity to primary colours. For example, I discovered that it varies from person to person and that color blindness is the result of a reduced sensitivity to a red or green color.”
You were awarded the Rumford Medal from the Royal Society of London for your work in 1860. But perhaps a more beautiful recognition was the color photograph you took next. “I had Thomas Sutton take three photos of a ribbon of tartan (Scottish fabric that is also used to make kilts, ed.), each time with a different color filter – red, green or blue – in front of the lens. By projecting the three photos over each other, you got a color photo. We presented it at a lecture in 1861 before the Royal Institution. They were amazed. ”
You also made a name for yourself in another area:astronomy. You focused on Saturn's rings in 1855. Why? “Very simple, really:Cambridge University awarded the Adams Prize in 1855 for the essay that best explained the stability of Saturn's rings. I had just graduated and was able to spend my time in Cambridge doing the things I liked. I was mesmerized by this topic since childhood.
Recent observations had shown that the rings did not always have the same structure. The question was:what kind of material were the rings made of? Pierre-Simon Laplace had previously said that if the rings were solid, they should consist of loose, concentric rings. I built on this and used Newton's mechanics to show that the rings couldn't be massive, because then they had to be pulled toward the planet. And rings of gas or liquid were also not possible, because unstable waves would arise in them.
My solution:the rings consisted of small, loose particles. I called them "brick bats." I also built a model of a wheel with small balls as extra proof. I was delighted to win the prize! I received a nice compliment from Sir George Bidell Airy, one of the judges:my work was 'one of the most remarkable applications of mathematics in physics that I have ever seen'."
Thinking about energy of gases at Saturn's rings led you to new insights into the velocity of atoms in a gas. At that time your most famous work. Tell me about that. “I came across work by the German Rudolf Clausius, in which he stated that particles in a gas collide with each other. The amount of collisions strongly determines how fast a gas moves. At that time, everyone thought that all molecules of a gas had the same speed. That couldn't be the case, because not every molecule collides equally often. In my opinion it was not possible to know exactly the speed of every molecule. What you could do was make a kind of probability distribution, based on how many molecules have a certain speed. I developed a formula for that distribution.”
Today we know that formula as the Maxwell-Boltzmann distribution, because Ludwig Bultzmann extended the work. A sensational find, because you brought the concept of statistics into thermodynamics. “You know, I knew I was on a new path, but I had no idea what it would bring to physics. I could only guess about that. The field of thermodynamics was still quite new and the concept of "molecules" was not yet widely accepted. But it's nice to hear that I was on the right track.”
Let's talk about electromagnetism. How did your ideas about this come about? “In my time, many people were concerned with electricity and magnetism. This was created in the twenties (of the nineteenth century, ed.) thanks to the Danish physicist Hans Christian Ørsted. He saw the magnetic needle of a compass move when a current ran in a copper wire nearby. That was the first indication that electricity and magnetism must have something to do with each other.
Michael Faraday was one of the many who was inspired by this work. He himself also conducted experiments with electricity and magnetism and discovered, among other things, the effect that a moving magnet in a coil generates an electric current, or 'magnetic induction'. When I started as a professor at King's College in London, I started to study electromagnetism. Faraday's explanation of the effects he saw really appealed to me."
What explanation was that? “Many people in my day thought in terms of a force acting at a distance, the way Newton had described for gravity. Faraday, on the other hand, saw forces as fields spreading through a medium in our space. He explained his phenomena with electric and magnetic sources that emit forces as waves, along so-called field lines, lines of force .”
I contacted Faraday by letter, which he found remarkable since I was forty years his junior. I then elaborated his concepts of fields and field lines into mathematical field equations in three dimensions. My school friend Peter (Guthrie Tait, ed.) helped me with the complicated vector algebra that came with it. So I ended up with a collection describing the electrical and magnetic effects that were now known. But then I discovered something remarkable…”
“I discovered that Ampere's Law was not complete. According to this law, a circular magnetic field is created around a wire through which electric current flows. When I compared the equations of this law with the other equations, I noticed that they didn't quite match up. To make it symmetrical, I added an extra term to the equation, the displacement current. Adding this term, my equation said that a changing electric field generates a magnetic field. Right, that had not yet been demonstrated in experiments, but that should be a matter of time.”
Now that the equations were symmetrical, what could you do with them? “Yes, with a little algebra you got two almost identical equations, one for the electric field and one for the magnetic field. The solution of these equations are waves of electric and magnetic fields. But now comes the most wonderful thing of all:when I calculated the speed at which these waves had to travel, I arrived at a number that was very close to the speed of light!
A complete surprise. I wasn't into light at all. I never had the slightest suspicion that light could have anything to do with electricity or magnetism. And here it just rolled out of my equations. I knew what light was:an electromagnetic wave. In fact, light, electricity and magnetism could all be described as electromagnetic fields!
Let's end with a bit of poetry. You have written many poems in your life. Would you like to close with a nice poem? “Of course. How about a poem about love. This is part of a poem I wrote for my wife Katherine in 1858:
Oft in the night, from this lone roomI long to fly o'er land and sea,To pierce the dark, dividing gloom,And join myself to thee.
And thou to me wouldst gladly fly,I know thee well, my own true wife!We feel, that when we live not nigh,We lose the crown of life.
Yet soon I hope, at dead of night,To meet where all is strange beside,And mid the train's resounding flightTo have thee by my side."
Would you like to ask James Clerk Maxwell a question yourself? Which can! We are curious about your funniest, craziest or most exciting questions to Maxwell. Send them – no later than April 19 – to [email protected], stating:'Contest for Handsome Heads'. We include the most original question in the article and try to answer it as best as possible. You also have a chance to win the beautiful book 'Canon of physics' worth € 42.50 offered by the Dutch Physics Association (NNV). Read more about this competition here.