Schematic drawing of one of the tubes used in Thomson's third experiment. Rays originate at the cathode on the left and pass through a slit in the anode into a bell jar containing gas at low pressure. The deflected paths of the rays are photographed against a ruled glass plate.

J.J. Thomson, "Cathode Rays," The London, Edinburgh, and Dublin Philosophical Magazine and Journal of Science, Fifth Series, October 1897. p. 301

1997- American Institute of Physics