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Wikipedia:
"Crookes tubes evolved from the earlier Geissler tubes, experimental tubes which are similar to modern neon tube lights. Geissler tubes had only a low vacuum, around 10−3 atm (100 Pa),[6] and the electrons in them could only travel a short distance before hitting a gas molecule. So the current of electrons moved in a slow diffusion process, constantly colliding with gas molecules, never gaining much energy. These tubes did not create beams of cathode rays, only a colorful glow discharge that filled the tube as the electrons struck the gas molecules and excited them, producing light."
"Crookes tubes were used in dozens of historic experiments to try to find out what cathode rays were.[12] There were two theories: British scientists Crookes and Cromwell Varley believed they were 'corpuscles' or 'radiant matter', that is, electrically charged atoms. German researchers E. Wiedemann, Heinrich Hertz, and Eugen Goldstein believed they were 'aether vibrations', some new form of electromagnetic waves, and were separate from what carried the current through the tube.[13][14] The debate continued until J.J. Thomson measured their mass, proving they were a previously unknown negatively charged particle, which he called a 'corpuscle' but was later renamed as 'electron'.
Maltese cross
"Julius Plücker in 1869 built an anode shaped like a Maltese Cross in the tube. It was hinged, so it could fold down against the floor of the tube. When the tube was turned on, it cast a sharp cross-shaped shadow on the fluorescence on the back face of the tube, showing that the rays moved in straight lines. After a while the fluorescence would get 'tired' and decrease. If the cross was folded down out of the path of the rays, it no longer cast a shadow, and the previously shadowed area would fluoresce stronger than the area around it."
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