Editing Cathode ray (section)

===Electrostatic deflection===
Cathode rays path can be deflected by an [[electric field]].  [[Heinrich Hertz]] built a tube with a second pair of metal plates to either side of the cathode ray beam, a crude [[Cathode-ray tube|CRT]]. If the cathode rays were [[charged particle]]s, their path should be bent by the [[electric field]] created when a [[voltage]] was applied to the plates, causing the spot of light where the rays hit to move sideways. He did not find any bending, but it was later determined that his tube was insufficiently evacuated, causing accumulations of [[surface charge]] which masked the electric field. Later Arthur Schuster repeated the experiment with a higher vacuum. He found that the rays were attracted toward a positively charged plate and repelled by a negative one, bending the beam. This was evidence they were negatively charged, and therefore not electromagnetic waves.
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