Sir Joseph John Thomson (18 December 1856 – 30 August 1940) was a British physicist. He won the 1906 Nobel Prize in Physics for his work on how electricity moves through gases. In 1897, he proved that cathode rays are made of tiny, negatively charged particles (now called electrons) that are much smaller than atoms and have a very high charge-to-mass ratio. The electron was the first subatomic particle ever discovered.

Thomson discovered the first evidence of isotopes in a non-radioactive element in 1912 while studying canal rays (positive ions). He and Francis William Aston studied positively charged particles using a new method called mass spectrometry, which helped create the mass spectrograph.

Thomson was a highly influential teacher. Seven of his students later won Nobel Prizes: Ernest Rutherford (Chemistry 1908), Lawrence Bragg (Physics 1915), Charles Barkla (Physics 1917), Francis Aston (Chemistry 1922), Charles Thomson Rees Wilson (Physics 1927), Owen Richardson (Physics 1928), and Edward Appleton (Physics 1947). His son, George Paget Thomson, shared the 1937 Nobel Prize in Physics with Clinton Davisson for showing how electrons can bend when passing through crystals.

Biography

Joseph John Thomson was born on 18 December 1856 in Cheetham Hill, Manchester. His mother, Emma Swindells, was from a family that worked in the textile industry. His father, Joseph James Thomson, owned a bookstore that his great-grandfather started. Joseph John had a brother named Frederick Vernon Thomson, who was two years younger than him. Thomson was quiet and deeply religious.

Thomson’s early education took place in small private schools, where he showed great talent and interest in science. In 1870, he entered Owens College in Manchester (now the University of Manchester) at the age of 14. There, he studied under Balfour Stewart, a physics professor who introduced him to scientific research. Thomson began experiments with electricity and published his first scientific paper. His parents planned to send him to work as an apprentice engineer at Sharp, Stewart & Co, a company that made trains, but these plans ended when his father died in 1873.

In 1876, Thomson moved to Trinity College, Cambridge. In 1880, he earned a B.A. in mathematics, achieving the second-highest honor in his exams and winning a prize. The next year, he became a Fellow of Trinity College. In 1883, he received an M.A. degree, also winning another prize.

On 22 December 1884, Thomson was named Cavendish Professor of Physics at the University of Cambridge. This surprised many because other candidates were older and had more lab experience, while Thomson was known for his work in mathematics and was considered highly talented.

In 1908, Thomson was knighted. In 1912, he was honored with the Order of Merit. At Oxford University, he gave a lecture in 1914 titled The Atomic Theory. In 1918, he became Master of Trinity College, Cambridge, a role he held until his death on 30 August 1940. His ashes are buried in Westminster Abbey, near the graves of Isaac Newton and his former student, Ernest Rutherford.

Rutherford later took over Thomson’s position as Cavendish Professor. Six of Thomson’s research assistants and colleagues (Charles Glover Barkla, Niels Bohr, Max Born, William Henry Bragg, Owen Willans Richardson, and Charles Thomson Rees Wilson) won the Nobel Prize in Physics. Two others (Francis William Aston and Ernest Rutherford) won the Nobel Prize in Chemistry. Thomson’s son, George Paget Thomson, won the 1937 Nobel Prize in Physics for proving that electrons have wave-like properties.

Research

Thomson's important work, Treatise on the Motion of Vortex Rings, won an award and showed his early interest in how atoms are structured. In this work, Thomson used math to describe how Lord Kelvin's idea of atoms as swirling vortices might move.

Thomson wrote many papers about both math and experiments related to electricity and magnetism. He studied James Clerk Maxwell's theory about light and electricity, introduced the idea that a charged particle has a type of mass called electromagnetic mass, and showed that a moving charged object appears to gain mass.

Much of Thomson's work on modeling chemical processes can be seen as an early form of computational chemistry. In his book Applications of Dynamics to Physics and Chemistry (1888), Thomson explored how energy changes using math and theory, suggesting that all energy might be kinetic energy. His next book, Notes on Recent Researches in Electricity and Magnetism (1893), expanded on Maxwell's work and was sometimes called "the third volume of Maxwell." In this book, Thomson focused on physical experiments and included many diagrams of equipment, such as tools for studying electricity in gases. His third book, Elements of the Mathematical Theory of Electricity and Magnetism (1895), became a popular textbook that introduced many topics clearly.

In 1896, Thomson gave four lectures at Princeton University, which were later published as Discharge of Electricity Through Gases (1897). He also gave six lectures at Yale University in 1904.

Before Thomson, scientists like William Prout and Norman Lockyer thought atoms were made from smaller units, but they believed these units were as big as hydrogen atoms. In 1897, Thomson was the first to suggest that atoms contain a smaller unit, more than 1,000 times smaller than an atom, which we now call the electron. Thomson discovered this by studying cathode rays, which were also called Lenard rays at the time. He found that these rays traveled farther through air than expected for an atom-sized particle. By measuring the heat from the rays and comparing it to how they bent in a magnetic field, Thomson estimated their mass. His experiments showed that cathode rays were much lighter than hydrogen atoms and that their mass was the same no matter which atom they came from. He concluded that these rays were made of very light, negatively charged particles that are a basic part of all atoms. He called these particles "corpuscles," but later scientists used the name "electron," first suggested by George Johnstone Stoney in 1891.

In April 1897, Thomson had early signs that cathode rays could be bent by electricity, though earlier scientists like Heinrich Hertz thought they could not. A month later, Thomson found that he could reliably bend the rays using an electric field if the discharge tube had very low pressure. By comparing how cathode rays bent in electric and magnetic fields, Thomson got more accurate measurements of their mass-to-charge ratio, which became a standard method for studying electrons. In 1899, he measured the charge of an electron as 6.8 × 10 esu.

Thomson believed the corpuscles came from the small amounts of gas inside his cathode-ray tubes. This led him to conclude that atoms can be divided and that corpuscles are their basic parts. In 1904, Thomson proposed a model of the atom as a positively charged sphere with negatively charged corpuscles moving inside it. He called this the "plum pudding model," where electrons were like raisins in a pudding, though they moved rapidly rather than staying still.

Thomson made his discovery around the same time as Walter Kaufmann and Emil Wiechert, who also found the correct mass-to-charge ratio for electrons.

The name "electron" became widely used by scientists, partly because of support from George Francis FitzGerald, Joseph Larmor, and Hendrik Lorentz. Stoney had first suggested the name in 1891 for the basic unit of electrical charge, which had not yet been discovered. Thomson initially avoided using "electron" because he disliked the idea of a "positive electron" as a unit of positive charge. He preferred "corpuscle," which he defined as negatively charged. By 1914, he used "electron" in his book The Atomic Theory. In 1920, Rutherford and others named the hydrogen ion's nucleus the "proton," creating a distinct name for the smallest known positively charged particle.

In 1912, Thomson and his assistant, F. W. Aston, studied positively charged particles called canal rays. They passed neon ions through electric and magnetic fields and observed two spots on a photographic plate, showing neon has two types of atoms with different masses (neon-20 and neon-22). This was the first proof that a stable element has isotopes. Frederick Soddy had earlier proposed isotopes to explain radioactive decay.

Thomson's method of separating neon isotopes by mass was the first example of mass spectrometry, later improved by F. W. Aston and A. J. Dempster.

Earlier, scientists debated whether cathode rays were like light (aether) or material particles. Thomson tested the idea that cathode rays were material by studying their movement in magnetic fields. He used a Crookes tube to produce cathode rays, which passed through an anode into a bell jar. A magnet deflected the rays, and Thomson used a screen to see their path. He found that the deflection was the same no matter the anode material or gas in the jar, suggesting the rays were the same everywhere.

Supporters of the aether theory believed cathode rays were immaterial, but Thomson tested whether the charge could be separated from the rays. He built a Crookes tube with an electrometer to study this.

Family

In 1890, Thomson married Rose Elisabeth Paget at the church of St Mary the Less. Rose was the daughter of Sir George Edward Paget, a physician and Regius Professor of Physic at Cambridge. She had an interest in physics. Starting in 1882, women were allowed to attend lectures and demonstrations at the University of Cambridge. Rose attended these events, including Thomson’s lectures, which led to their meeting and eventual marriage.

They had two children: George Paget Thomson, who later received a Nobel Prize for his research on the wave properties of the electron; and Joan Paget Thomson (later Charnock), who became an author. She wrote children’s books, non-fiction, and biographies.

Commemoration

In November 1927, Thomson opened the Thomson building, named after him, at Leys School in Cambridge.

In 1991, the thomson (symbol: Th) was proposed as a way to measure mass-to-charge ratio in mass spectrometry, named after Thomson.

J J Thomson Avenue, located on the West Cambridge campus of the University of Cambridge, is named after Thomson.

The Thomson Medal Award, supported by the International Mass Spectrometry Foundation, is named after Thomson.

The Institute of Physics Joseph Thomson Medal and Prize is named after Thomson.

Thomson Crescent in Deep River, Ontario, is connected to Rutherford Ave.