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## The 10 best physicists – no. 5 – James Clerk Maxwell

At number 5 in The Guardian’sten best physicists” is the Scottish theoretical physicist James Clerk Maxwell.

As the caption above says, James Clerk Maxwell is probably one of the least known of the physicists in this list, and yet one of the most important. It was through his theoretical work that a full understanding of electromagnetism became possible. His four equations, known as Maxwell’s equations, are as important to understanding electromagnetism as Newton’s laws of motion are to understanding mechanics. In some ways, Maxwell was to Faraday what Newton was to Galileo. Neither Galileo nor Faraday had the mathematical ability to write in mathematics the experimental results they obtained in mechanics and electricity and magnetism respectively. Newton wrote the mathematical equations to explain Galileo’s experiments in mechanics; and similarly Maxwell wrote the mathematical equations to explain the experiments Faraday had been doing on electricity and magnetism.

## Maxwell’s brief biography

James Clerk was born in 1831 in Edinburgh, Scotland. He was born into a wealthy family, and later added Maxwell to his name when he inherited an estate as part of his wider family’s wealth. His mother died when Maxwell was eight years old, and at ten years of age his father sent him to the prestigious Edinburgh Academy.

At the age of 16, in 1847, Maxwell left Edinburgh Academy and started attending classes at Edinburgh University. His ability in mathematics quickly became apparent. At the age of only 18 he contributed two papers to the Transactions of the Royal Society of Edinburgh, and in 1850, at the age of 19, he transferred from Edinburgh University to Cambridge. Initially he attended Peterhouse College, but transferred to the richer and better known Trinity College. He graduated from Trinity College Cambridge in 1854 with a degree in mathematics. He graduated second in his class.

In 1855 he was made a fellow of Trinity College, allowing him to get on with his research. But in November 1856 he left Cambridge, being appointed Professor of Natural Philosophy at the University of Aberdeen in Scotland. He was 25 years of age, and head of the Natural Philosophy department, some 15 years younger than any of his colleagues there.

Maxwell left Aberdeen in 1860 to become Professor of Natural Philosophy at Kings College, University of London. He resigned in 1865 to return to his estate in Scotland, and for the next 6 years he got on with his research, and due to being independently wealthy he didn’t need a formal paying position at a university. But in 1871 he was tempted back into university life, he was appointed the first Cavendish Professor of Physics at Cambridge University, and given the role of establishing the Cavendish Laboratory, which opened in 1875.

Maxwell died in 1879 of abdominal cancer, and is buried in Galloway, Scotland, near where he grew up.

## Maxwell’s scientific legacy

Maxwell is best known amongst physicists for two main areas of work, his work on electromagnetism and his work on the kinetic theory of gases. As I mentioned above, his work on electromagnetism can be likened to a certain extent to Newton’s work on mechanics. Newton was able to take the experimental results Galileo had found on the behaviour of moving bodies, and find the underlying laws of mechanics to explain them, and to express these in mathematical form. This is essentially what Maxwell did for the work of Faraday, he was able to find the laws which explained the observations Faraday had been making, and was a sufficiently skilled mathematician to write these laws in equation form.

Maxwell first presented his thoughts on electromagnetism in a paper in 1855, when he was 24 years old. In this he reduced all the known knowledge of electromagnetism as it existed in 1855 into a set of differential equations with 20 equations and 20 variables. In 1862 he showed that the speed of propagation of an electromagnetic field was approximately the same as the speed of light, something Maxwell thought was unlikely to be a coincidence. This was the first indication that light was a form of electromagnetism, but a form to which are eyes are senstive.

In 1873 Maxwell reduced the 20 differential equations of his 1855 paper into the four differential equations which are familiar to every undergraduate physics student. These equations, expressed in their differential form are
$\boxed{ \begin{array}{lcll} \nabla \cdot \vec{D} & = & \rho & (1) \\ & & & \\ \nabla \cdot \vec{B} & = & 0 & (2) \\ & & & \\ \nabla \times \vec{E} & = & - \frac{\partial \vec{B}}{\partial t} & (3) \\ & & & \\ \nabla \times \vec{H} & = & - \frac{\partial \vec{D}}{\partial t} + \vec{J} & (4) \end{array} }$

The symbol $\nabla$ is known as the vector differential operator, or del, and I have explained del in this blog.

The four equations can also be written in integral form, which many people find easier to understand. In integral form, the equations become

$\boxed{ \begin{array}{lcll} \iint_{\partial \Omega} \vec{D} \cdot d\vec{S}& = & Q_{f}(V) & (5) \\ & & & \\ \iint_{\partial \Omega} \vec{B} \cdot d\vec{S} & = & 0 & (6) \\ & & & \\ \oint_{\partial \Sigma} \vec{E} \cdot d\vec{\l} & = - & \iint_{\Sigma} \frac{\partial \vec{B} }{\partial t} \cdot d\vec{S} & (7) \\ & & & \\ \oint_{\partial \Sigma} \vec{H} \cdot d\vec{l} & = & I_{f} + \iint_{\Sigma} \frac{\partial \vec{D} }{\partial t} \cdot d\vec{S} & (8) \end{array} }$

## Kinetic theory of gases

Maxwell also did important work on one of the other main areas of physics research in the 19th Century – the kinetic theory of gases, a branch of thermodynamics. Maxwell and the Austrian physicist Ludwig Boltzmann independently came up with an expression which describes the distribution of speeds of the atoms or molecules in a gas. The speed depends on the temperature, the higher the temperature the faster the atoms or molecules move. But Maxwell and Boltzmann showed that not all the atoms will be moving at this speed; some will be moving faster and some will be moving slower. The distribution of speeds is known as the Maxwell-Boltzmann distribution.

## The theory of colour vision

Less well known to most physicists is the work Maxwell did on optics, and on colour vision. He was the first person to show how a colour image could be created from combining three images taken through red, green and blue filters. This lies at the foundation of practical colour photography, and is also how our colour television sets work.

I think it is true to say that most physicists would place Maxwell in their top four physicists. His contributions to physics are immense, creating the formal framework for our understanding of electromagnetism, without which the modern world would not be possible. That he is so unknown outside of the world of physics is strange, but whereas Newton had his $F=ma$ and Einstein his $E=mc^{2}$, Maxwell’s equations are far too complicated to have permeated into the consciousness of the public. But they are every bit as important as Newton and Einstein’s.

You can read more about James Clerk Maxwell and the other physicists in this “10 best” list in our book 10 Physicists Who Transformed Our Understanding of the UniverseClick here for more details and to read some reviews.

Ten Physicists Who Transformed Our Understanding of Reality is available now. Follow this link to order

## The 10 best physicists – no. 6 – Michael Faraday

At number 6 in The Guardian’s list of the top ten physicists is Michael Faraday.

Michael Faraday is known both as a physicist and a chemist. In the field of physics the contributions which put him in this list are mainly due to his groundbreaking work on understanding electromagnetism. Amongst other things, he introduced the idea of the electromagnetic field, he discovered the link between magnetism and light, and he discovered electromagnetic induction and invented the first electric motor.

Faraday was born in 1791 in Newington Butts which is now part of London, but at the time was in suburban Surrey. He was born into a strictly religious family, his father James was a member of a sect of Christianity known as the Glassites. His family was not wealthy, and Faraday only received a basic education. By the age of 14 he was working as an apprentice bookbinder. It was during his 7 years working as an apprentice bookbinder that Faraday set about educating himself.

At the age of 20, Faraday attended his first lecture given by Humphrey Davy at the Royal Institution. Davy had become one of the foremost chemists of his time, and was a superb lecturer and showman. Faraday was captivated by Davy’s lectures, and wrote copious notes on what he was seeing and hearing in these lectures.

Faraday lovingly collected the lecture notes he had taken, and bound them in a 300-page volume that he sent to Davy, at the same time asking for a job. Davy did not have a job to offer him, but in 1823 Davy suffered an accident in the laboratory, and offered a position to Faraday working as his assistant. This was the beginning of Faraday’s scientific career, and he became one of the best experimentalists physics has seen.

Faraday married Sarah Barnard in 1821, they had met through church. Both were devoutly religious, and his religion influenced Faraday throughout his life. He twice refused the offer to become President of the Royal Society, and also refused the offer of a knighthood. During the Crimean war of 1853-56, Faraday was asked to help develop chemical weapons but refused. In 1848 he was awarded and accepted a “grace and favour” house in Hampton Court, a house which became known as Faraday House. Faraday and his wife had no children, and he died in 1867 at the age of 75. He turned down the offer to be buried at Westminster Abbey, and instead is buried at Highgate Cemetery.

The list of Faraday’s contributions to physics is quite long, so I will only mention the highlights. In 1821, hearing about the work which the Danish scientist Hans Christian Ørsted had done on electromagnetism, Faraday and co-workers Davy and William Hyde Wollaston showed that a wire carrying an electric current set up a circular magnetic field about it. Unfortunately, in publishing this work, Faraday failed to mention the contributions of Davy and Wollaston, which strained the relationship between Faraday and his mentor Davy, and led to Faraday being assigned other work for several years, effectively stopping his work on electromagnetism for a period.

In 1831 Faraday conducted a series of experiments which showed the phenomenon of electromagnetic induction. Faraday wrapped two insulated wires around a iron ring, one coil on each side of the ring. Upon passing a current through one coil, he found that a current was produced in the other coil. This is the basis of how transformers work, and was a major breakthrough in our understanding of electromagnetism.

This work showed that a changing electric field produces a magnetic field,and a changing magnetic field produces an electric field. This is now known as Faraday’s law. Faraday went on from this work to produce the first ever electrical dynamo, a device which produces electricity and is the basis of the electric generators today used in power stations.

Later in his life, in the 1860s, Faraday showed that the plane of linearly polarised light could be rotated if the light passed through a magnetic field which was in the same direction as the direction of the light’s travel. This phenomenon, now known as the Faraday effect, was the first indications of a link between light and magnetism, and was a crucial step in Maxwell’s later work which showed that light was just a manifestation of electromagnetism to which our eyes are sensitive.

There is probably no other series of discoveries in the world of Physics which have had more of an influence on our modern everyday lives than those made in the first half of the 1800s in understanding electromagnetism. Almost every device we use today, our entire modern lives, relies on discoveries which were made in large part by Faraday. The unit of capacitance, the Farad, is named in his honour. He is the only physicist in this top ten list who had no formal education, and yet his contributions to our understanding of physics are immense.

Does Faraday deserve his place in this list of the ten best physicists?