Joseph John Thomson Jeremy Plett Born: December 18, 1856 in Cheetham, England (near Manchester) Died: August 30, 1940 Joseph John Thomson was the son of a bookseller and began his college career at Owens College in Manchester at the age of fourteen. Strangely, Thomson’s father had intended that JJ study to become an engineer but this was too expensive for the family. Two years later, when Thomson was only sixteen, his father died. Shortly after this event, Thomson received a scholarship at Cambridge University’s prestigious Trinity College. It was here that Thomson would spend the rest of his life. Thomson was a gifted mathematician and got a bachelor’s degree in mathematics in 1880. In 1884, Thomson was given the opportunity to do experimental research and teach at the Cavendish Laboratory. Thomson closely monitored his students and their progress and he was a very helpful instructor as well as a great teacher. Thomson must have particularly aided one female student named Rose Paget, who became his wife in 1890. J.J. and Rose had two children, one of whom, Sir George Paget Thomson, became a distinguished physicist himself, winning the Nobel Prize in Physics in 1937. George Thomson’s prize came as a result of his co discovery of the diffraction of electrons by crystals. In addition to his scientific interest, J.J. Thomson loved athletics and never missed a chance to see the local cricket and rugby matches. Thomson is sometimes remembered as the “father of the electron.” He is credited with the discovery that all matter contains particles much smaller than atoms and that these particles are of the same type. We now call these particles electrons. This discovery was made while Thomson was working with cathode rays. Thomson was trying to learn the nature of these mysterious rays, which was widely speculated upon but not known. Thomson performed three major experiments in 1897 which led to his grand discovery. For the first experiment, Thomson built a cathode ray tube and used a magnet to bend the rays. In this experiment, Thomson sought to determine whether or not the charge that the rays were known to possess could be separated from the rays. Thomson found that when the rays were bent through the slit and allowed access to the electrometer it measured a large negative charge. When the rays were bent so that they missed the slit and when the rays were not bent at all the electrometer measured a small charge. Thomson reasoned that the charge could not be removed from cathode rays. Thomson knew that a negatively charged ray should bend in both magnetic and electric fields. In a magnetic field, the rays were observed to bend as expected. In electric fields, however, physicists could not get the cathode ray to bend. Thomson was also aware that charges do not bend in an electric field if they are surrounded by a conductor. He figured that the gas had not been completely removed from the cathode ray tube. The remaining gas could then be blamed for the current problem. If the remaining gas, which surrounded the cathode ray, could conduct electricity, then it could act as a shield and prevent the deflection of the cathode ray. To test this, Thomson went to great lengths to remove as much gas from the tube as possible before experimenting. After this was done, the rays were finally deflected by an electric field as they were supposed to be. After these two experiments, Thomson already figured he was dealing with beams of particles rather then “mysterious rays.” Said Thomson, “I can see no escape from the conclusion that [cathode rays] are charges of negative electricity carried by particles of matter, but what are these particles? Are they atoms? Are they molecules, or perhaps some smaller form of matter?” In Thomson’s third experiment, he sought to find some of the properties of these particles. Although he was unable to measure the charge or mass of an individual particle, he was able to measure how much the beam bent in a magnetic field and how much energy the beams carried. In this process, he was able to calculate a ratio of mass to charge. What Thomson found was not what he expected. The ratio of mass to charge was greater than one thousand times smaller than that of a charged hydrogen atom. Thomson concluded that the particles that make up a cathode ray must be extremely light or heavily charged. Thomson’s discovery was great, but his idea that corpuscles (electrons) may form all matter has since been found to be incorrect. Although we now know that there are other subatomic particles, Thomson was right in saying that electrons are a fundamental part of every atom. His “Plum Pudding” model was the first legitimate attempt at an atomic model and was improved upon in the following years. Because of his discovery of the electron, J.J. Thomson became a very celebrated physicist. He was awarded the Nobel Prize for physics in 1906 and in 1908 he was knighted. In 1909 he was made president of the British Association for the Advancement of Science and attended a conference in Winnipeg, Manitoba with this title attached to his name. Thomson is remembered as a great teacher as well and seven of his students went on to win Nobel Prizes of their own. Because of this, it is clear that Thomson’s value to scientific development goes far beyond the discovery that he is most famous for. J.J. Thomson entered the world of physics at just the right time. Before him came much research into the fields of electricity, magnetism, and thermodynamics, which set the stage for much further discovery. Physics, however, was thought to be a dying science and many believed everything important had already been discovered. Thomson, along with several others, put an end to this thought and set the science of physics on a course for fantastic advancement over the following decades and, indeed, the following century as well. Sir J.J. Thomson wrote a number of books including A Text Book of Physics- Properties, which was published in 1909 and Elements of the Mathematical Theory of Electricity and Magnetism, which was published in 1919. A library at Cambridge University still has 6 boxes full of papers that he wrote. For those interested, further research on Thomson and the discovery of the electron can be done even on the University of Manitoba campus. Also, page 70 in Quantum Theory has a few words about Thomson and the discovery of the electron. Bibliography Numbers 1 to 3 are excellent resources and have much information on the life and work of Sir J.J. Thomson. 1) http://www.geocities.com/MotorCity/Lane/6341/JJ.html 2) http://www.scs.k12.tn.us/STT99_WQ/STT99/Bartlett_HS/stephensonp/Trish/thomson.htm 3) http://www.britannica.com/nobel/micro/591_84.html 4) http://web.lemoyne.edu/~giunta/jthomson.html (Nobel Prize Acceptance Speech) 5) http://www.chemheritage.org/EducationalServices/chemach/ans/jjt.html (Best Portrait) 6) http://antoine.frostburg.edu/chem/senese/101/atoms/slides/sld008.htm (Plum Pudding Model) 7) http://www.sci.tamucc.edu/pals/morvant/genchem/atomic/page6.htm (Plum Pudding Model) 8)http://library.trin.cam.ac.uk/search/aThomson%2C+J./athomson+j/1%2C20%2C59%2CB/exact&FF=atho mson+j+j+sir+joseph+john+1856-1940&1%2C29%2C (publications) 9) http://nobelprize.org/physics/laureates/1906/thomson-lecture.html (Real Nobel Prize Lecture) .