Philip Lenard

Philip Lenard, 1862 - 1947, did an experiment to find out whether cathode rays, like ultraviolet light, would pass through a quartz window in the wall of a discharge tube, finding they would not. He was eventually able to develop a cathode ray tube with a thin aluminium window that was thick enough to maintain the vacuum in the tube, but thin enough to allow cathode rays to escape.
Lenard observed that cathode rays continued through air for about 10cm, and several metres in a vacuum without being weakened. He was able to show that if cathode rays consisted of particles with mass, the mass was much less than the mass of an atom.

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