Diagram of J. J. Thomson's apparatus for studying 'positive rays'. Large bulb with A) anode, C) cathode in front of the cylinder of soft iron with very narrow copper tube passing through. Particles protected from magnetic field until leaving tube then pass between poles of electromagnet P,P) or plates, E,E). Positive particles then strike photographic plate. J. J. Thomson (1856-1940) an English physicist and Nobel laureate in physics. Dated 20th century.