Two unsung national heroes

The scientists Henry Cavendish and Paul Dirac deserve to be much better known than they are.

Happy birthday Royal Society. This month Britain's most prestigious scientific institution is 350 years old. To celebrate this important milestone in our country's intellectual history, I'm going to tell you about two British scientific geniuses who deserve to be much better known than they are at the present time. Their names are Henry Cavendish and Paul Dirac, and they are both great unsung national heroes.

The 18th-century chemist and physicist Henry Cavendish was once called "the richest of the learned and the most learned of the richest". He pioneered the study of gases, developing methods for collecting them and weighing them. Earning a distinguished reputation both in the UK and abroad, he was made a fellow of the Royal Society in 1760 and the Institute of France selected him as one of its eight foreign associates. When he died, a leading French scientist wrote to a colleague that Cavendish was a "model for those who cultivate the physical sciences". The Cavendish Laboratory in Cambridge is named after him.

Cavendish's most important achievement was to discover that hydrogen was a distinct substance. He called it "inflammable air" and it was the first of the elements to be identified. Although others, such as Robert Boyle, had prepared hydrogen gas earlier, Cavendish was the person who recognized that it was an element. Cavendish attempted to calculate the density of hydrogen in a 1766 paper "On Factitious Airs" and came remarkably close bearing in mind the difficulty of the task and the relative crudeness of his apparatus. Later, the French scientist Antoine Lavoisier reproduced Cavendish's experiment and gave the element its name.

Cavendish revolutionised our understanding of our planet by showing that water is a compound of oxygen and hydrogen and that air is a mixture of different gases. For many centuries it had been believed that the world was made of four elements - earth, air, fire and water. Cavendish's work showed that this idea was mistaken. He observed that hydrogen reacts with oxygen to form water. When he set light to hydrogen, water appeared on the surface of the glass vessel in which it was held. By producing water from two other substances, Cavendish demonstrated that water could not be an element. In the process of these experiments, he also discovered nitric acid.

Cavendish was interested in learning about the composition of Earth's atmosphere. He determined that air is made up of 80% nitrogen (although he called it "phlogisticated air") and 20% oxygen. He also noticed that a small fraction of the "phlogisticated air" behaved differently from the rest. This was the inert gas argon, which was only recognized as a distinct substance more than a century later. In 1781 he carried out observations to find out whether or not the composition of air changes. He analysed the air on 60 different days and in different locations and found no discernible difference in the proportion of oxygen in the air at the various sites and times.

Apart from his investigations in chemistry, Cavendish's other great breakthrough was his experiment to determine the mass and density of the Earth. In 1798 he was the first person to measure the force of gravity between masses in a laboratory, and to produce an accurate measurement for Earth's density. Cavendish calculated that the mass of the Earth was approximately 6.5 million billion tons with a density about 5.5 times that of water. These estimates are remarkably close to the figures produced by modern scientific techniques. His method became known as the Cavendish experiment and the accuracy of this experiment was not improved on for nearly a century. He also made advances in the study of heat, electrostatic force and electricity, measuring the strength of currents by giving himself an electric shock and recording the extent of the pain.

Our main source of knowledge about Cavendish's career is a book by the physician and chemist George Wilson, The Life of the Honourable Henry Cavendish, published in 1851. Cavendish was born in 1731 into one of Britain's leading aristocratic families. He was the son of Lord Charles Cavendish and the grandson of William Cavendish, 2nd Duke of Devonshire. His mother was Lady Anne Grey, daughter of Henry Grey, 1st Duke of Kent. His family could trace its ancestry back to the Norman period and was closely linked with several other aristocratic families.

At the time of his birth, Cavendish's family was living in Nice, France. He began studying at Cambridge University at the age of 18 but left four years later without graduating. After undertaking the Grand Tour of Europe like other young aristocratic men of his generation, he settled in London and immersed himself in scientific studies. He performed his experiments in an outbuilding in the garden of his Clapham Commons estate. Neighbours would point out the building to their children and tell them it was where the world was weighed. Despite inheriting a fortune, he lived a frugal existence. When Cavendish died in 1810 he was one of the wealthiest men in Britain, leaving property worth £700,000.

Paul Dirac has been described as the second greatest scientist of the 20th century, the most distinguished British scientist since Isaac Newton, and one of the founding fathers of modern physics. He was a man who investigated the sub-atomic world through the power of pure mathematics. One physicist declared that Dirac's discoveries were like "exquisitely carved statues falling out of the sky, one after another".

Born in Bristol in 1902, he was a pioneer of quantum mechanics (the study of particles within atoms) and quantum electrodynamics, and he even came up with an early version of string theory (the idea that the universe is made up of tiny vibrating string-like particles). In 1933 he shared the Nobel Prize for physics with the Austrian scientist Erwin Schrodinger for his work on atomic theory. At the age of just 31, Dirac was the youngest person to win physics' greatest prize. Without Dirac's insight into the electron's behaviour, it could be argued we wouldn't have mobile phones, computers or any other device that uses electronics. His work is still consulted today by scientists working on projects such as the Large Hadron Collider.

His book The Principles of Quantum Mechanics, published in 1930, is regarded as a significant moment in the history of science and soon became one of the key textbooks on the subject. In the same year he was elected a fellow of the Royal Society on the first occasion his name was submitted, an unusual achievement that demonstrates the high regard in which he was held by his scientific peers. During his career he received both the Royal Medal and the Copley Medal, the two highest honours the Royal Society can award. In 1973, he was appointed to the Order of Merit.

Among his many achievements, he came up with the "Dirac equation", an unlikely marriage of Einstein's theory of relativity and quantum theory. By combining these two theories in the way he did, Dirac managed to explain the electron's mysterious spin and magnetism. What's more, on the basis of this equation, he predicted the existence of anti-matter in the universe. Most scientists judge this to be the supreme achievement of 20th century physics and this Dirac equation is still widely used today.

According to Dirac's equation, there had to be a particle with the same mass as the electron but with a positive instead of a negative charge. The equation only worked if you assumed that such an "anti-electron" existed. His colleagues were sceptical about the idea but Dirac was adamant and it wasn't long before he was proved right. Shortly afterwards, this predicted anti-particle, the positron, was discovered by the American scientist Carl Anderson. Soon the concept of anti-matter became a cornerstone of physics. Scientists now think that anti-matter makes up half the universe.

Dirac's genius was such that he seemed to be able to identify laws of nature with pure thought. He proposed the existence of anti-matter not on the basis of experimental observation but because his own mathematical logic told him it must exist. The mathematics of his equation, he argued, was so harmonious that reality had to reflect it. He strongly believed that the fundamental laws of the universe have mathematical beauty. He once asserted that "it is more important to have beauty in one's equations than to have them fit experiment" and that "God used beautiful mathematics in creating the world".

Dirac's exceptional ability in mathematics and science showed itself to his school teachers early in his life. He went on to obtain degrees in electrical engineering and mathematics at Bristol University before becoming a researcher at Cambridge. By the time he had achieved his doctorate, he had already had 11 papers published in scientific journals including one which established many of the chief principles of quantum mechanics.

He quickly built a name for himself, being appointed a fellow of St John's College, Cambridge at the age of 25. Eventually he was awarded the university's distinguished Lucasian Chair of Mathematics in 1932, a role once held by Isaac Newton. Dirac held the post for 37 years. After emigrating to America, Dirac spent the last 13 years of his life working at the University of Miami and Florida State University. He died in 1984 aged 82 and is buried in Tallahassee, Florida.

In 1995, a plaque bearing the Dirac equation was unveiled in his honour at Westminster Abbey with a speech from Professor Stephen Hawking. Hawking was the first recipient of the Paul Dirac Medal which is awarded annually by the Institute of Physics for outstanding contributions to physics.

By this point, you're probably wondering why I've given an account of the achievements of these two eminent scientists when this column is supposed to be about disability. Well, there is considerable evidence to suggest that these two men were not only among the most highly regarded scientists this country has ever produced but also autistic. In my next column, I will explain how their autism, far from holding back their careers, may well have been the secret of their scientific success.

Further reading:
The Strangest Man: The Hidden Life of Paul Dirac by Graham Farmelo
For general information about autism - National Autistic Society

In this article, Victoria gives her personal views. These are not the views of the BBC.

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