Schematic drawing of the apparatus used in Thomson's first experiment. Cathode rays pass from the tube in the upper left into the larger bulb, where they are deflected with a magnetic field. When they are bent so as to enter the slits in the cylinders, the electrometer measures the charge transferred to the cylinder.

J.J. Thomson, "Cathode Rays," The London, Edinburgh, and Dublin Philosophical Magazine and Journal of Science, Fifth Series, October 1897. p. 295

1997- American Institute of Physics