Cathode Rays Among the experiments on electricity were some that involved sending electric currents through glass tubes containing various kinds of gas. When the current was turned on, the negative electrode, or cathode, glowed with a strange greenish light, and a similarly glowing greenish spot would appear on the opposite glass wall of the tube. It was clear that something was traveling in a straight line across the tube from the cathode; this "something" was named a cathode ray. Some suggested that cathode rays might be waves, like light or the recently discovered x-rays. But waves, as far as anyone knew then, couldn't carry electric charge; only particles could do that. That's why Thomson's experimental results convinced him that cathode rays had to be made up of particles.

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