Forces, Fields and Magnetism

A Little History Of Science: Forces, Fields and Magnetism

Dalton’s atom helped create modern chemistry, but there were other ways of looking at atoms. For a start, they could do much more than just combine to make compounds. Atoms don’t simply enter into chemical reactions. Both Davy and Berzelius had cleverly used the fact that atoms in a solution can be attracted to the positive or negative poles if an electric current is passed through the solution: atoms were part of ‘electricity’, too. In a solution of seawater, why would the sodium migrate to the negative pole, and the chlorine to the positive?

Such questions were hotly debated in the early nineteenth century. One of the chief investigators was Michael Faraday (1791– 1867). Faraday was a quite remarkable man. Born into an ordinary family, he received only a basic education. He spent his youth learning bookbinding, but he discovered science and spent his spare time reading anything he could find about it. A popular children’s book on chemistry fired his imagination, and a customer at the bookbinder’s shop where he worked offered him a ticket to hear one of Humphry Davy’s talks at the Royal Institution. Faraday listened in rapture and took careful notes in his neat handwriting.

Ever keen, he showed his notes to Davy, who was impressed by their accuracy, but he advised Faraday that there were no jobs in science, and bookbinding was a better trade for a man who needed to make a living.

Shortly afterwards, however, a laboratory assistant at the Royal Institution was sacked, and Davy offered Faraday the job. He stayed there the rest of his life, helping to make it a profitable place with a great reputation. Faraday’s early days at the Institution were spent in solving chemical problems for Davy. Faraday excelled in the laboratory, but he continued to read about more general scientific problems. He was a devout member of a particular group of Protestants; he devoted many hours to his Church, and his religious belief also guided his scientific enquiries. Quite simply, he thought that God had created the universe the way it is, but that human beings were capable of understanding how it all fits together.

Shortly after Faraday joined the Royal Institution, Davy and his new wife went on a tour of Europe, and they took Faraday with them. Davy’s aristocratic wife treated Faraday as a servant, but the eighteen-month tour allowed Faraday to meet many of the leading scientific figures in Europe. Returning to London, Faraday and Davy continued to work on many practical problems: what caused explosions in mines; how the copper bottoms of ships could be improved; what were the optical characteristics of glass? As Davy became increasingly concerned with scientific politics, so Faraday became increasingly his own master, turning his attention to the relationship between electricity and magnetism.

In 1820, the Danish physicist Hans Christian Oersted (1777– 1851) had discovered electromagnetism: the manipulation of an electric current so that it creates a magnetic ‘field’. Magnetism had long been known, and the compass, with its iron needle always pointing north, is still useful. Navigators had used compasses long before Columbus discovered America, and natural philosophers had puzzled over why only a few substances (such as iron) could be magnetised. Most things could not. The fact that compasses always pointed in the same direction meant that the earth itself acted as a huge magnet.

Oersted’s electromagnetism created a wave of scientific interest, and Faraday took up the challenge. In September 1821, he devised one of the most famous experiments in scientific history. Working with a small magnetic needle, he saw that the needle would continue to spin round if it was surrounded by wires carrying an electric current. While the electricity flowed through the coiled wire, it created a magnetic field to which the needle was continually attracted – spinning round and round. This was the result of what Faraday called ‘lines of force’, and he realised its significance. What he had done, for the first time, was to convert electrical energy (electricity) into mechanical energy (the movement or power of the rotating needle). He had invented the principle of all our electrical motors. These too convert electricity into power, in washing machines, CD players or vacuum cleaners.

Faraday continued to work with electricity and magnetism for the next thirty years. He was one of the most gifted experimenters who ever lived: thoughtful about planning his work and careful in carrying it out. His self-education had not included mathematics, so his scientific papers read much like his laboratory notebooks: detailed descriptions of his equipment, what he did and what he observed. His work also helped scientists understand the role of electrical charges in chemical reactions. By the early 1830s, he had added the electrical generator and the electrical transformer to his inventions. He made his electrical generator by moving a permanent magnet in and out of a coiled wire, which creates an electric current. To make his transformer, he passed an electric current through a wire wound around an iron ring, which caused a brief electrical current in another wire, wound around the opposite face of the ring. Faraday knew these experiments were crude, but he also knew he was on to something very important. The relationship between electricity and magnetism, and the conversion of electrical energy to mechanical energy, literally drive our modern world.

Faraday kept up his broad scientific interests, and spent much time sitting on scientific committees and running the Royal Institution. He started the Institution’s Christmas Lectures, which are still hugely popular today – you may have seen one on the television. But electricity and magnetism remained his chief love.

His fascination left us with a new vocabulary and many useful applications. He even made jokes about his inventions. When asked by a politician of the practical value of electricity, he is supposed to have said, ‘Why, sir, there is every probability that you will soon be able to tax it!’ Across the Atlantic, another world-changing upshot of the great interest in electricity and magnetism appeared: the electric tele- graph. Sending signals through electric wires started in the early 1800s, but the American Samuel Morse (1792–1872) developed the first long-distance telegraph. In 1844 he sent a message over thirty-eight miles (using the Morse Code that bears his name) from Washington, DC, to Baltimore. Telegraphic communication quickly developed all over the world, and the British used it to connect the outposts in their far-flung empire. It was now possible for people to communicate quickly with each other, and for news to be reported soon after it happened.

Faraday came up with the idea of a ‘field’ of action to explain why electricity and magnetism had their amazing properties. Fields (areas of influence) had been used by scientists before as they tried to explain the mysteries of chemical reactions, electricity, magnetism, light and gravity. These things took place, they thought, in a particular space or field, just as different games are played on a specific court, pitch or field. Faraday made this idea central to his explanation of electricity and magnetism, arguing that the important thing was to measure the area of activity rather than worry too much about what electricity, light or magnetism actually were. But the force of an electric field could be shown in experiments.

Faraday could not believe that something like gravity could exert its influence through a vacuum. Faraday solved this by assuming that there was no such thing as absolute emptiness.

Rather, he argued, space was filled with a very refined substance that was called the ‘aether’. This aether (it’s nothing to do with ether, the anaesthetic gas) made it possible for physicists and chemists to explain lots of things by direct influence. Thus, Faraday’s ‘fields’ around electric currents or magnets could be the result of the current or magnet stimulating the very refined matter that constituted the aether. Gravity was easier to explain in this way, too: otherwise it seemed to be some strange occult force like the magical powers of the older alchemists, something that moderns like Faraday did not believe in. The aether was not something you could see, or feel, but physicists thought it explained the results of their experiments. In Britain, they continued to use the aether idea until the early 1900s, when experiments showed that it did not actually exist.

Much of Faraday’s work on forces proved more useful. Later physicists extended it and provided better mathematical descriptions of electricity, magnetism and the many other phenomena that the physical world throws up when explored. Faraday was the last great physicist who didn’t use mathematics. The man who truly secured Faraday’s legacy was James Clerk Maxwell (1831–79), one of the new breed of mathematical physicists.

Maxwell is often spoken of in the same breath as Newton and Einstein. He was certainly one of the most creative physicists of all time. He was born in Edinburgh and educated there until he went to Cambridge University. He returned briefly to Scotland to teach, but in 1860 went to King’s College, London. There he spent some of his most productive years. He had already described the rings of the planet Saturn, but in London he developed a theory of colour and took the first colour photograph. He was always interested in electricity and magnetism, and brought them firmly together: after Maxwell, physicists could use mathematics to describe electromagnetism. Maxwell provided the mathematical tools and equations to describe Faraday’s ideas of the field. His equations showed that the electromagnetic force is a wave, and this was one of the most important discoveries in the whole of physics. This wave travels at the speed of light, and we now know that the light and energy from the sun come to us as electromagnetic waves. Indeed, Maxwell predicted the entire range of waves that we know: radio waves which allow radio broadcasts, microwaves in our kitchens, ultraviolet and infrared light waves above and below the colours of the rainbow, as well as X-rays and gamma waves, or rays. These waves are now part of everyday life.

Yet most of these forms of energy were still to be discovered when Maxwell predicted them, so it was not surprising that it took some time for his genius to be appreciated. His Treatise on Electricity and Magnetism (1873) is probably the most important physics book between Newton’s Principia and those of the twentieth century.

By the time he wrote this book, Maxwell had gone to Cambridge to organise the Cavendish Laboratory, where so much important physics research in the decades to follow would be done. Maxwell himself died young, aged forty-eight, but not before he had carried out fundamental research on how gases behave, using the special mathematical techniques of statistics. This allowed him to describe how the large numbers of atoms in a gas, each moving at slightly different speeds and in different directions, would produce the effects they do at different temperatures and pressures. He provided the mathematical tools to explain what Robert Boyle and Robert Hooke had observed all those years before.

Maxwell also developed the basic concept of ‘feedback mechanisms’: processes that go in loops, which he called ‘governors’. These mechanisms are very important in technology, in twentieth-century developments in artificial intelligence, and in computers. They also happen in our own bodies. For instance, when we get too hot, the body senses this and we sweat. The sweat cools our bodies as it evaporates. Or, if we are cold, we shiver, and the contractions of our muscles in the shiver produce heat which warms us. These feedback mechanisms help us maintain a constant body temperature.

Maxwell had a gentle sense of humour, was deeply religious and close to his wife, who kept a tight rein on him. At dinner parties, she was prone to say, ‘James, you’re beginning to enjoy yourself; it is time we go home.’ Luckily, she didn’t stop his pleasure in the laboratory.