Joseph John Thomson

Biography Joseph John Thomson was born on 18 December 1856 in Cheetham Hill, Manchester. His mother, Emma Swindells, came from a local textile family. His father, Joseph James Thomson, ran an antiquarian bookshop founded by Thomson's great-grandfather. Joseph John had a brother, Frederick Vernon Thomson, who was two years younger than he was. Thomson was a reserved yet devout Anglican.

Education Thomson's early education was in small private schools where he demonstrated outstanding talent and interest in science. In 1870, he was admitted to Owens College in Manchester (now the University of Manchester) at the unusually young age of 14, and came under the influence of Balfour Stewart, Professor of Physics, who initiated him into physical research. He began experimenting with contact electrification and soon published his first scientific paper. His parents planned to enroll him as an apprentice engineer to Sharp, Stewart & Co, a locomotive manufacturer, but these plans were cut short when his father died in 1873. and 2nd Smith's Prizeman). He obtained an M.A. (Adams Prizeman) in 1883.

Career On 22 December 1884, Thomson was appointed Cavendish Professor of Physics at the University of Cambridge. This appointment caused considerable surprise; candidates such as Osborne Reynolds and Richard Glazebrook were older and more experienced in laboratory work, whereas Thomson was known for his work as a mathematician—being recognised as an exceptional talent.

Thomson was knighted in 1908 and appointed to the Order of Merit in 1912. At Oxford, he gave the 1914 Romanes Lecture titled The Atomic Theory. In 1918, he became Master of Trinity College, Cambridge, a position he held until his death on 30 August 1940. His ashes rest in Westminster Abbey, near the graves of Isaac Newton and his former student, Ernest Rutherford.

Rutherford succeeded him as Cavendish Professor. Six of Thomson's research assistants and junior 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, and two (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 the wave-like properties of electrons.

Research Early work Thomson's prize-winning master's work, Treatise on the motion of vortex rings, shows his early interest in atomic structure. In it, Thomson mathematically described the motions of Lord Kelvin's vortex theory of the atom. was a readable introduction to a wide variety of subjects, and achieved considerable popularity as a textbook. He estimated the mass of cathode rays by measuring the heat generated when the rays hit a thermal junction and comparing this with the magnetic deflection of the rays. His experiments suggested not only that cathode rays were over 1,000 times lighter than the hydrogen atom, but also that their mass was the same in whichever type of atom they came from. He concluded that the rays were composed of very light, negatively charged particles which were a universal building block of atoms. He called the particles "corpuscles", but later scientists preferred the name electron, which had been suggested by George Johnstone Stoney in 1891, prior to Thomson's discovery.

In April 1897, Thomson had only early indications that the cathode rays could be deflected electrically (previous investigators such as Heinrich Hertz had thought they could not be). A month after Thomson's announcement of the corpuscle, he found that he could reliably deflect the rays by an electric field if he evacuated the discharge tube to a very low pressure. By comparing the deflection of a beam of cathode rays by electric and magnetic fields he obtained more robust measurements of the mass-to-charge ratio that confirmed his previous estimates. This became the classic means of measuring the charge-to-mass ratio of the electron. Later in 1899 he measured the charge of the electron to be of .

Thomson believed that the corpuscles emerged from the atoms of the trace gas inside his cathode-ray tubes. He thus concluded that atoms were divisible, and that the corpuscles were their building blocks. In 1904, Thomson suggested a model of the atom, hypothesizing that it was a sphere of positive matter within which electrostatic forces determined the positioning of the corpuscles.

Thomson made the discovery around the same time that Walter Kaufmann and Emil Wiechert discovered the correct mass to charge ratio of these cathode rays (electrons).

The name electron was adopted for these particles by the scientific community, mainly due to the advocation by George Francis FitzGerald, Joseph Larmor, and Hendrik Lorentz. The term was originally coined by George Johnstone Stoney in 1891 as a tentative name for the basic unit of electrical charge (which had then yet to be discovered). For some years Thomson resisted using the word "electron" because he didn't like how some physicists talked of a "positive electron" that was supposed to be the elementary unit of positive charge just as the "negative electron" is the elementary unit of negative charge. Thomson preferred to stick with the word "corpuscle" which he strictly defined as negatively charged. He relented by 1914, using the word "electron" in his book The Atomic Theory. In 1920, Rutherford and his fellows agreed to call the nucleus of the hydrogen ion "proton", establishing a distinct name for the smallest known positively-charged particle of matter (that can exist independently anyway).

Isotopes and mass spectrometry In the bottom right corner of this photographic plate are markings for the two isotopes of neon: neon-20 and neon-22.

In 1912, as part of his exploration into the composition of the streams of positively charged particles then known as canal rays, Thomson and his research assistant, F. W. Aston, channelled a stream of neon ions through a magnetic and an electric field and measured its deflection by placing a photographic plate in its path. This was the first evidence for isotopes of a stable element; Frederick Soddy had previously proposed the existence of isotopes to explain the decay of certain radioactive elements.

Thomson's separation of neon isotopes by their mass was the first example of mass spectrometry, which was subsequently improved and developed into a general method by F. W. Aston and by A. J. Dempster.

Experiments with cathode rays Earlier, physicists debated whether cathode rays were immaterial like light ("some process in the aether") or were "in fact wholly material, and ... mark the paths of particles of matter charged with negative electricity", quoting Thomson.

Electrical charge The cathode-ray tube by which J. J. Thomson demonstrated that cathode rays could be deflected by a magnetic field, and that their negative charge was not a separate phenomenon.

While supporters of the aetherial theory accepted the possibility that negatively charged particles are produced in Crookes tubes, they believed that they are a mere by-product and that the cathode rays themselves are immaterial. Thomson set out to investigate whether or not he could actually separate the charge from the rays.

Thomson constructed a Crookes tube with an electrometer set to one side, out of the direct path of the cathode rays. Thomson could trace the path of the ray by observing the phosphorescent patch it created where it hit the surface of the tube. Thomson observed that the electrometer registered a charge only when he deflected the cathode ray to it with a magnet. He concluded that the negative charge and the rays were one and the same.

Thomson imagined the atom as being made up of these corpuscles orbiting in a sea of positive charge; this was his plum pudding model. This model was later proved incorrect when his student Ernest Rutherford showed that the positive charge is concentrated in the nucleus of the atom.

Other work In 1905, Thomson discovered the natural radioactivity of potassium.

In 1906, Thomson demonstrated that hydrogen had only a single electron per atom. Previous theories allowed various numbers of electrons.

From 1916 to 1918, Thomson chaired the "Committee appointed by the Prime Minister to enquire into the Position of Natural Science in the Educational System of Great Britain". The Report of the Committee, published in 1918, was known as the Thomson Report.

Family In 1890, Thomson married Rose Elisabeth Paget at the church of St Mary the Less. Rose, who was the daughter of Sir George Edward Paget, a physician and then Regius Professor of Physic at Cambridge, was interested in physics. Beginning in 1882, women could attend demonstrations and lectures at the University of Cambridge. Rose attended demonstrations and lectures, among them Thomson's, leading to their relationship.

They had two children: George Paget Thomson, who was also awarded a Nobel Prize for his work on the wave properties of the electron; and Joan Paget Thomson (later Charnock), who became an author—writing children's books, non-fiction, and biographies.

Recognition Memberships Year Organisation Type 1884 Royal Society Fellow 1902 American Academy of Arts and Sciences International Honorary Member 1903 American Philosophical Society International Member 1903 National Academy of Sciences International Member 1905 Royal Society of Edinburgh Honorary Fellow

Awards Year Organisation Award Citation 1894 Royal Society Royal Medal "For his contributions to mathematical and experimental physics especially to electrical theory." 1902 Smithsonian Institution Hodgkins Medal — 1902 Royal Society Hughes Medal "For his numerous contributions to electric science, especially in reference to the phenomena of electric discharge in gases." 1906 Royal Swedish Academy of Sciences Nobel Prize in Physics "In recognition of the great merits of his theoretical and experimental investigations on the conduction of electricity by gases." 1914 Royal Society Copley Medal "On the ground of his discoveries in physical science." 1915 Royal Society of Arts Albert Medal — 1922 Franklin Institute Franklin Medal "For service as teacher and leader in electricity and the constitution of matter." 1925 Institution of Electrical Engineers Faraday Medal — 1938 Institution of Civil Engineers Kelvin Gold Medal —

Commemoration In November 1927, Thomson opened the Thomson building, named in his honour, in the Leys School, Cambridge.

In 1991, the thomson (symbol: Th) was proposed as a unit to measure mass-to-charge ratio in mass spectrometry in his honour.

J J Thomson Avenue, on the University of Cambridge's West Cambridge site, is named after Thomson.

The Thomson Medal Award, sponsored 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, connects with Rutherford Ave.