The Life and Times of J. J. Thomson (1856-1940)
At the time of Thomson's birth:
- Franklin Pierce was president of the United States
- Boers established South African Republic
- Crimean War ended
- Franklin Delano Roosevelt was president of the United States
- First electron microscope demonstrated
- France surrendered to Germany
- 1861-1865: American Civil War
- 1870-1914: Realistic Period of English literature
- 1899-1902: Boer War
- 1914-1918: World War I
- 1910-1936: Reign of George V in Great Britain
- 1939-1945: World War II
- Claude Monet (1840-1926) French painter
- Friedrich Nietzsche (1844-1900) German philosopher
- Gabriel Fauré (1845-1924) French composer
- Henry Ford (1863-1947) American industrialist
- Wassily Kandinsky (1866-1944) Russian painter
- Ernest Rutherford (1871-1937) British physicist
- Niels Bohr (1885-1962) Danish physicist
- Wolfgang Pauli (1900-1958) German physicist
- 1858: British government took direct control of India
- 1869: Transcontinental railroad completed
- 1877: Thomas Edison invented phonograph
- 1886: Statue of Liberty dedicated
- 1911: Ernest Rutherford explained atom's structure
- 1922: British Broadcasting Corporation (BBC) founded
- 1932: James Chadwick discovered the neutron
- 1936: First paperbacks published by Penguin Books
Physicist Sir J. J. Thomson researched the behavior of electricity, discovering the electron in 1897. He was awarded the Nobel Prize in physics, in 1906.
A scientist of diverse interests; J. J. Thomson was awarded the Nobel Prize in physics in 1906 for his theoretical and experimental research on the behavior of electricity in gases. As one consequence of that research, Thomson discovered the electron in 1897. He also was interested in a number of other topics, including optics, magnetism, radioactivity, photoelectricity, and thermionics (a branch of physics relating to the emission of charged particles from an incandescent source).
Joseph John Thomson was born at Cheetham Hill, a suburb of Manchester, England, on December 18, 1856. His father was a bookseller and publisher who specialized in antique volumes. J. J., as he was widely known, originally planned to become an engineer, and arrangements were made for him to apprentice with a friend of his father's. When the senior Thomson died in 1870, however, the family could no longer afford to pay the expense of J. J.'s apprenticeship, and he enrolled at Owen's College, now the University of Manchester. Thomson studied mathematics, physics, and chemistry under a distinguished science faculty, and with the encouragement of Thomas Baker, a professor of mathematics, Thomson applied for and won a scholarship to Baker's alma mater, Trinity College, Cambridge.
Fellowship Brings Thomson to Cambridge for a Four-Decade Stay
Thomson entered Trinity College in 1876 and majored in mathematics, beginning an affiliation with Cambridge University that would last the rest of his life. Although some of the most exciting and important physical and chemical research was going on within a few steps of Thomson's college, he made no attempt to find out about them. However, his single-minded attention to mathematics was rewarded when, in 1880, he earned a second place in the college examination on that subject.
Thomson's first published work dealt with the research of a fellow scholar at Cambridge whom he had never met, James Clerk Maxwell . Maxwell had only recently devised his mathematical theory of electromagnetism, and Thomson became intrigued by some of its special implications. For instance, when Thomson analyzed the properties that might be expected of a charged sphere that is placed in motion, he discovered that the apparent mass of the sphere would increase as a result of its gaining electrical charge. Although Thomson did not pursue this line of research, the finding was clearly a preview of the concept of mass-energy equivalence that would be proposed by Albert Einstein a decade later.
In 1881 Thomson was awarded a fellowship that allowed him to stay on at Trinity College. The thesis he wrote in competition for that fellowship involved an analysis of some physical and chemical deductions that could be drawn from some very general mathematical laws, an approach Thomson used frequently in his research. He argued that it is sometimes useful simply to derive the physical implications of mathematical expressions without worrying about the physical reality that might be involved. One advantage of this approach, he said, was that new and unanticipated lines of research might be revealed.
Thomson did not disregard the role of physical reality in his research, however; he also argued that the best way to attack a problem may sometimes be to devise analogies or to construct models of the phenomenon under investigation. An example of this approach was an essay he wrote in 1882 for the Adams Prize competition. The subject of that competition was vortex rings, spinning cloud-like assemblies somewhat similar to smoke rings. Vortex rings were of great interest to scientists toward the end of the nineteenth century because many thought that atoms might consist of such arrangements. Thomson's essay won the prize but, probably more important, it eventually led him into a line of research—electrical discharges in gases—from which he was to produce his greatest accomplishments.
In 1884, Lord Rayleigh retired as Cavendish Professor of Physics—one of the most prestigious chairs of science in the English-speaking world—and he recommended that Thomson be appointed to replace him. Word of the recommendation caused an uproar within the Cambridge scientific community; numerous well-qualified and famous scholars wanted the position for themselves and were outraged that a young man of twenty-eight was being considered for the post. Critics of Thomson's candidacy perceived his background in experimental science as weak since most of his earlier studies and research had been in mathematics or theoretical science. Still, the selection committee, consisting of Lord Kelvin, George Gabriel Stokes, and George Howard Darwin, chose Thomson as Rayleigh's replacement and director of the world-famous Cavendish Laboratory at Cambridge.
Research on Electrical Discharge in Gases Reveals the Electron
The research field to which Thomson now turned was one related to the topic of his Adams Prize essay—electrical discharge in gases—which had become extremely popular among physicists during the preceding decade, largely as the result of the work of Julius Plücker, Johann Wilhelm Hittorf, William Crookes, Eugen Goldstein, and others. Most experiments followed a common model: an electrical discharge is caused to pass through a gas under very low pressure in a glass tube. Under these circumstances, a glowing beam is observed to follow the electrical discharge from one end of the tube to the other. The beam, called a cathode ray, can be deflected by an electrical or magnetic field superimposed on the tube.
The primary question that remained in the mid-1890s concerned the nature of cathode rays. Were they streams of charged particles, as Crookes and others believed, or were they of the luminiferous ether as most German physicists thought? Thomson turned his attention to the resolution of this question. A key development in his approach to the problem was the development of better equipment; he was able to show, with better vacuums, a decrease in the ambiguous and contradictory results obtained by other researchers. Using improved equipment, Thomson accomplished the deflection of cathode rays by an electrical field, which was strong evidence that the rays did consist of particles.
Thomson then went one step further: he developed an experiment in which cathode rays were deflected by both magnetic and electrical fields. By measuring the angle at which the rays were deflected by such fields of any given 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 value of e/m was the same for any gas used in the experiment (that is, 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).
Thomson also extended his research to other phenomena caused by electrical discharges, such as the discharge from a negatively charged heated wire. He found an occurrence similar to that observed in the original glass tube experiments, in which particles with the same e/m ratio could be detected. He concluded that some fundamental particle with a constant e/m ratio was present in all of these experiments and, hence, was a component of all atoms. The term used by Thomson for these particles, corpuscle, was soon replaced by a name suggested earlier by G. J. Stoney, electron. Thomson's reports on his discoveries to the British Association in 1889 were so well documented that the existence of a new subatomic particle was almost immediately accepted by scientists worldwide.
Thomson's discovery raised a number of fundamental questions about atomic structure. For nearly a century, scientists had thought of the atom as some kind of indivisible, uniform particle or mass of material, but Thomson had shown that this view was untenable, and that the atom must consist of at least two parts, one of which was the newly discovered electron. To account for his discovery, Thomson proposed a new model of the atom, sometimes referred to as the "plum pudding" atom. In this model, the atom was thought to consist of a cloud of positive charge in which are embedded discrete electrons, much as individual plums are embedded in the traditional English plum pudding. However, this model was never very successful, and, in the work of Thomson's successor, Ernest Rutherford, a better atomic picture would soon evolve.
In recognition of his research on electrical discharges in gases, Thomson was awarded the 1906 Nobel Prize in physics. Two years later, he was knighted for his accomplishments in science. By this time, however, Thomson had gone on to a new field of research, the study of the positively charged "canal" rays that are also produced during electrical discharge in gases. Thomson used a method similar to that with which he discovered the electron, the deflection of canal rays with magnetic and electrical fields. The instrument he developed to accomplish the procedure was the forerunner of today's mass spectrometer, in which particles of differing e/m ratios can be separated from each other.
Thomson's instrumentation eventually became so sophisticated that he was able to separate two isotopes of neon, neon-20 and neon-22, from each other. He was not able to completely interpret the results of this experiment, however, and he eventually turned the work over to one of his graduate students, Francis Aston . Aston's continuation of this work resulted not only in a more refined form of the spectrometer, but also in a confirmation that he and Thomson had indeed discovered the first isotopes of a stable element.
Career Concludes with Accomplishments in Teaching and Administration
The work on canal rays marked the end of Thomson's most creative years. His efforts after 1912 focused more on teaching and administration, although he did remain active in research to some extent. He was elected president of the Royal Society in 1915 and was appointed Master of Trinity College in 1918. He resigned as Cavendish professor in the following year, but was then appointed to an honorary chair which allowed him to maintain university privileges. Thomson was succeeded in the Cavendish chair by one of his greatest students, Ernest Rutherford.
Thomson's impact on science was just as notable for his skills as a teacher and administrator. He was responsible for the expansion of the Cavendish Laboratories (on two occasions) as well as for its efficient operation for thirty-five years. A tribute to his talent for finding, educating, and nurturing young researchers is the fact that no less than seven of his students eventually received Nobel Prizes in the sciences. A few years before Thomson's death, he was honored by a dinner given in his honor at Cambridge. The list of guests contained most of the leading figures in physical research of the day. At the dinner, Thomson was given a testimonial signed by more than two hundred friends, students, and colleagues. Thomson died in Cambridge on August 30, 1940, and was laid to rest in Westminster Abbey close to Isaac Newton and Charles Darwin.
- Treatise on the Motion of Vortex Rings, [London], 1883.
- Applications of Dynamics to Physics and Chemistry, [London], 1888.
- Notes on Recent Research in Electricity and Magnetism, [Oxford], 1893.
- Conduction of Electricity through Gases, [Cambridge], 1903.
- The Corpuscular Theory of Matter, [London], 1907.
- Rays of Positive Electricity and their Application to Chemical Analysis, [London], 1913.
- The Electron in Chemistry, [Philadelphia], 1923.
- Recollections and Reflections, [London], 1936.