Joseph John Thompson

Joseph John Thompson

1. Who Were They?

   • Thompson became a physicist by default. His father intended him to be an engineer, which in those days required an apprenticeship, but his family could not raise the necessary fee. Instead young Thomson attended Owens College, Manchester, which had an excellent science faculty. He was then recommended to Trinity College, Cambridge, where he became a mathematical physicist.
   • In 1884 he was named to the prestigious Cavendish Professorship of Experimental Physics at Cambridge, although he had personally done very little experimental work. Even though he was clumsy with his hands, he had a genius for designing apparatus and diagnosing its problems. He was a good lecturer, encouraged his students, and devoted considerable attention to the wider problems of science teaching at university and secondary levels.

2. What They Found?

   • In 1897 Joseph John (J. J.) Thomson discovered the electron in a series of experiments designed to study the nature of electric discharge in a high-vacuum cathode-ray tube, an area being investigated by numerous scientists at the time.
   • And then in 1904 Thomson suggested a model of the atom as a sphere of positive matter in which electrons are positioned by electrostatic forces. His efforts to estimate the number of electrons in an atom from measurements of the scattering of light, X, beta, and gamma rays initiated the research trajectory along which his student Ernest Rutherford moved.

3. What was Their Experiment?

   • He estimated the mass of rays (cathode) by measuring the heat created when the rays hit a thermal junction and comparing this with the magnetic deflection of the rays. His experiments showed not only that cathode rays were over 1,000 times lighter than the hydrogen atom, but that their mass was the same in whichever type of atom they came from also. He decided that the rays were made of very light, negatively charged particles which were a universal building block of atoms.

4. The Physicist Him Self

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