Thomson JJ
Full Name: Sir Joseph John Thomson
Nickname/Alias: J.J. Thomson
Achievements: The electron
Born: December 18, 1856; Cheetham Hill, near Manchester, England
Died: August 30, 1940; Cambridge, Cambridgeshire, England (Aged 83)
Field & Discipline: Science; Physics
Education: Owens College, 1871-76;Trinity College, University of Cambridge,1876-80
Major Work:“The Corpuscular Theory of Matter” (1907 )
Life & Times:
In 1876 Thomson won a mathematics scholarship at Trinity College, Cambridge, where he would remain for the rest of his life. In 1881 he began working at the Cavendish Lab under [worked under] Rayleigh* and wrote his first important paper which appeared in the “Philosophical Magazine” and contained an application of the new and notyet fully accepted electromagnetic theory of [work related to] Maxwell* to the motion of a charged sphere.
Analyzing the properties that might be expected, Thomson showed that the sphere would have apparent added mass due to the charge and proportional to the electrostatic energy. This was the first step towards [work related to] Einstein's* famous law of the equivalence of mass and energy published a decade later.
In 1884, Thomson was chosen to replace Rayleigh as director of the Cavendish. Thomson was then for several years largely occupied in building a comprehensive explanation of the conduction of electricity through gases, and in particular of the phenomenon of cathode rays - a subject that had become extremely popular among physicists during the preceding decade, largely as a result of the work of [work related to] Plucker*, [work related to] Hittorf*, [work related to] Crookes*, [work related to] Goldstein* and others.
These men had established that if an electrical discharge is caused to pass through a gas under very low pressure in a glass tube, a glowing beam - called a cathode ray - is seen to follow the electrical discharge from one end of the tube to the other, and can be deflected by an electrical or magnetic field superimposed on the tube.
Research into cathode rays were galvanized in 1895 by the discovery by [influenced by] Roentgen* of X-rays, a previously unsuspected form of radiation that was also produced in gas discharge tubes (but from the anode rather than the cathode).
Soon Thomson, working with [collaborated with] Rutherford*, found that passing X-rays through gases greatly increased their ability to conduct electricity, as the X-rays ionized the gases (they converted gas atoms into ions, which carry an electrical charge and so are good carriers of current), and that the resulting conduction resembled in some ways the conduction by ions during electrolysis of a solution.
In 1897 Thomson found that cathode rays were deflected by electric fields, strong evidence that cathode rays were rapidly-moving charged particles. Thomson then developed experiments in which the rays were deflected by both magnetic and electrical fields. By measuring the angle at which the rays were deflected by fields of different magnitudes, he was able to calculate the ratio of the electrical charge to the mass (e/m) for the particles that made up the rays.
He found that the e/m for the cathode ray "corpuscles" (as Thomson called them) was constant for any gas used in the experiment (whatever particle it was that made up the cathode rays occurred in all gases and was, therefore, a component of all of the different atoms of which those gases were made), and that this e/m ratio was over 1000 times larger than the ratio for the hydrogen ion, the lightest atom known.
He speculated that these particles had a mass over 1,000 times smaller than hydrogen (today it is known that the correct ratio is closer to 1,800:1), and that particles with this small mass were universal constituents of matter, since they were the same whatever the chemical nature of the gas carrying the discharge and the electrodes through which it entered and left.
Thomson made the first public declaration of his revolutionary findings in an evening speech to the Royal Institution on 30 April 1897. He then continued his attempt to confirm that, as he suspected, the "corpuscles," later named "electrons" (a word coined a few years earlier by G.J. Stoney for the charge on a hydrogen atom regarded as a natural unit of charge) carried the same charge as a hydrogen ion, which would then prove that he had discovered a new entity 1,000 times lighter than the simplest atom.
This was confirmed during 1898 when Thomson extended his research to other phenomena caused by electrical discharges, and proved that particles with the same value e/m were released from a negatively charged hot wire and from a negatively charged zinc plate illuminated by ultraviolet light.
In this second experiment, using the apparatus designed by [used gizmo designed by] CTR Wilson*, he was able to measure the actual charge by condensing drops of water on the “subatomic” particles to form a mist, establishing the size of the drops from their rate of fall.
Thomson did find some detractors, however, including the German physicist [priority dispute with] Lenard*, who for a period bitterly claimed priority over the discovery, and by a few scientists such as the German chemist [opposed by] Ostwald*, who until his death in 1932 refused to believe in the existence of either atoms or electrons.
Over the next few years Thomson also developed a model of the atom that incorporated his discovery, sometimes referred to as the "plum pudding" atom, in which he proposed that the atom is a diffuse sphere of positive electrical charge in which discrete, negatively-charged electrons are embedded.
However, this model was never very successful, and from the work of Rutherford, Thomson's successor at the Cavendish, and [superseded by] Bohr* a better picture - of the nuclear atom - would soon evolve.
Thomson was awarded the 1906 Nobel Prize in Physics, and in 1908 he was knighted for his scientific achievements.
Between 1906 and 1914 Thomson entered his second and last great period of research, which he devoted to the study of "canal rays", streams of positively charged ions (first discovered by Eugen Goldstein), which Thomson named “positive rays.”
Using magnetic and electric fields to deflect these rays, in 1912 he found that ions of neon gas are deflected by different amounts, indicating that they consist of a mixture of ions with different charge-to-mass ratios.
The British chemist [work related to] Soddy* had earlier proposed the existence of isotopes, an idea proved by Thomson to be correct when he identified the isotope neon-22 in 1912. This work was later continued by one of Thomson's students, Francis Aston (developer of the mass spectrograph), and others, and lead to the discovery of many other isotopes, vital to the understanding of the heavy radioactive elements, such as uranium and radium.
By the end of his career, seven Nobel Prizes were awarded to those who worked under Thomson, including his own son, George Thomson and the German physicist [taught] Born*.
Extra Connections: Knew Prime Minister [knew] Balfour*.
His work related to that of [work related to] Becquerel* and [work related to] Lorenz*,
Fellow member of Society for Psychical Research with physicists [fellow-psychic with] Lodge*, author [fellow-psychic with] Carroll*, evolutionist [fellow-psychic with] Wallace*, poet [fellow-psychic with] Tennyson,* and [fellow-psychic with] Conan Doyle*
He taught [taught] Langevin*, [taught] Bragg* and [taught] Oppenheimer*.
Taught at Owens College by [taught by] O Reynolds*
Assessment: He helped revolutionize the knowledge of atomic structure by his discovery of the electron (1897).
Oneliner: JJ Thomson, discoverer of the electron
Language: English
Father: Joseph James Thomson (d. 1873)
Mother: Emma Swindells (d. 1901)
Siblings: One younger brother
Spouse: Rose Elizabeth Paget (married 1890)
Children: one son: Sir George Paget Thomson (Nobel Prize for Physics in 1937); a daughter
Bibliography:
- Dictionary of Scientific Biography.
- Encyclopedia Britannica.
- Thomson, G.P., J.J. Thomson and the Cavendish Laboratory in His Day, London, 1964