J.J. Thomson

Cheetham Hill

Joseph John Thomson was born on 18 December 1856 in Cheetham Hill, north Manchester. His father, Joseph James Thomson, ran an antiquarian bookshop on Market Street, a business founded by his great-grandfather. His mother, Emma Swindells, came from a textile family. It was a modest, respectable, lower-middle-class Manchester upbringing in the kind of neighbourhood where getting on meant getting educated.

His father intended him to become an engineer and tried to apprentice him to Sharp, Stewart and Company, the locomotive manufacturers in Manchester. While they waited for a place, the young Thomson was sent to Owens College to fill the time. He was 14 years old. Then, in 1873, his father died. Thomson was 16. The family could no longer afford the apprenticeship premium, and the engineering career was gone. He stayed at Owens on scholarships because it was the only route left open to him. It turned out to be one of the most consequential accidents in the history of science.

Cheetham Hill in the 1860s was a densely packed neighbourhood of terraced streets and small businesses, sitting between the centre of Manchester and the open ground to the north. It produced factory workers, shopkeepers, and the occasional oddity who ended up changing the world. Thomson was the oddity.

Owens College

Owens College was Manchester's answer to the ancient universities. Founded in 1851 with money left by John Owens, a cotton merchant, it occupied a house on Quay Street before moving to the Oxford Road campus that would eventually become the University of Manchester. When Thomson arrived in 1870, it was still a young institution, but it was already attracting serious academics and building a reputation for science and engineering that the city's industrial economy demanded.

Thomson excelled. He studied mathematics and physics under Balfour Stewart and Thomas Barker, both of whom recognised that they had something unusual on their hands. His mathematical ability was extraordinary. In 1876, aged 19, he won a scholarship to Trinity College, Cambridge. By 1880, he was Second Wrangler in the Mathematical Tripos, the equivalent of finishing second in the country. Manchester had given him the foundation. Cambridge would give him the laboratory.

It's worth pausing on what Owens College meant. This was not Oxford or Cambridge. It was a new kind of institution, built for a new kind of student, funded by Manchester money and staffed by people who believed that a lad from Cheetham Hill with a gift for mathematics deserved the same shot as anyone from the Home Counties. Thomson was proof that the model worked.

The Cavendish

At Cambridge, Thomson's rise was rapid. He was Second Wrangler in 1880, became a Fellow of Trinity College in 1881, and in 1884 was appointed Cavendish Professor of Experimental Physics. He was 27 years old. The appointment surprised some, including Thomson himself, who was succeeding Lord Rayleigh in a role that had previously been held by James Clerk Maxwell. A bookseller's son from Cheetham Hill, orphaned at 16 and educated on scholarships, was now running one of the most important physics laboratories in the world.

The Cavendish Laboratory under Thomson became a magnet for talent. He had a gift for identifying and nurturing brilliance in others that was at least as important as his own research. The list of physicists who trained under him reads like a roll call of twentieth-century science. Ernest Rutherford came from New Zealand. Charles Wilson came from Scotland. Francis Aston came from Birmingham. They came because the Cavendish, under Thomson, was where the questions that mattered were being asked.

He ran the laboratory for 35 years. In that time, it produced seven Nobel Prize winners from among his research students and assistants, a record that speaks as much to his ability as a teacher and leader as to his own scientific output. He created an environment where exceptional people could do exceptional work, and he had the generosity to let them.

The Electron

In the 1890s, Thomson turned his attention to cathode rays, the mysterious glowing streams that appeared when electrical current was passed through a glass tube containing very little gas. The scientific community was divided. German physicists believed cathode rays were waves in the ether. British and French physicists suspected they were particles. Nobody had been able to settle it.

Thomson designed a series of experiments at the Cavendish in 1897 that were elegant in their simplicity. He measured the ratio of the charge to the mass of the cathode ray particles by deflecting them with electric and magnetic fields. The results were extraordinary. Whatever these particles were, they were far smaller than the smallest known atom. They were identical regardless of which gas was in the tube or which metal the cathode was made from. They appeared to be a fundamental component of all matter.

He called them corpuscles. The name didn't stick. The world settled on electrons, a term coined by the Irish physicist George Johnstone Stoney a few years earlier. But the discovery was Thomson's. He had proved that the atom, which for over two thousand years had been assumed to be the indivisible building block of everything, was itself made up of smaller parts. It was one of the most important discoveries in the history of physics, and it came from a man who had started out waiting for an engineering apprenticeship in Manchester.

His model of the atom, with negatively charged electrons embedded in a positively charged sphere, became known as the plum pudding model. It was eventually superseded by Rutherford's nuclear model in 1911, but it was Thomson who had opened the door. Without the electron, there is no Rutherford, no Bohr, no quantum mechanics. Everything that followed started in the Cavendish with Thomson's cathode ray tubes.

The electron wasn't his last discovery. In 1913, working with his student Francis Aston, Thomson passed a stream of neon ions through electric and magnetic fields and found that they separated into two distinct groups of different mass. A single element, two different atomic masses. It was the first evidence that stable elements could exist as isotopes, and it laid the groundwork for mass spectrometry. Aston went on to build the first mass spectrograph and won the Nobel Prize in Chemistry in 1922. Another student. Another Nobel. Another idea that started with Thomson.

Legacy

The Nobel Prize in Physics came in 1906, awarded for his investigations into the conduction of electricity by gases. He was knighted in 1908. He received the Order of Merit in 1912. He served as President of the Royal Society from 1915 to 1920. The honours accumulated in the way they tend to when someone has done something genuinely extraordinary, and Thomson accepted them with the quiet reserve of a man who was more interested in the next experiment than the last award.

He became Master of Trinity College in 1918 and resigned the Cavendish chair the following year. His successor was his former student Ernest Rutherford, the New Zealander who had arrived at the Cavendish as Thomson's research student in 1895, gone to McGill in Canada, then to Manchester in 1907, where he developed the nuclear model of the atom and carried out the first artificial splitting of the atom at the very college Thomson had attended. Rutherford came back to Cambridge in 1919 to take over from the man who had trained him. The bookseller's son from Cheetham Hill ended up running the richest college in Cambridge.

He died on 30 August 1940. His ashes were interred in Westminster Abbey, near Isaac Newton and his former student Rutherford, who had been laid to rest there in 1937. The professor and his greatest student, side by side. It was the kind of company that would have seemed unimaginable to anyone standing on Market Street in 1856, looking at an antiquarian bookshop and wondering what the boy inside would amount to.

But the most remarkable part of the Thomson story is what happened next. His son, George Paget Thomson, won the Nobel Prize in Physics in 1937 for demonstrating that electrons could behave as waves. The father had proved the electron was a particle. The son proved it was also a wave. Between them, they captured one of the deepest truths in physics: that matter is stranger than anyone had imagined. Two Nobel Prizes. One family. And it started in Cheetham Hill.

There is an old story, almost certainly apocryphal, that at a Cavendish dinner Thomson raised his glass and proposed a toast: "To the electron: may it never be of any use to anybody!" Every device with a screen, every light switch, every computer, every phone in every pocket on every street in the world runs on the particle he discovered. The electron turned out to be useful after all. And it started with a lad from north Manchester who couldn't afford an apprenticeship.