<P> When they reached the anode end of the tube, they were traveling so fast that, although they were attracted to it, they often flew past the anode and struck the back wall of the tube . When they struck atoms in the glass wall, they excited their orbital electrons to higher energy levels, causing them to fluoresce . Later researchers painted the inside back wall with fluorescent chemicals such as zinc sulfide, to make the glow more visible . </P> <P> Cathode rays themselves are invisible, but this accidental fluorescence allowed researchers to notice that objects in the tube in front of the cathode, such as the anode, cast sharp - edged shadows on the glowing back wall . In 1869, German physicist Johann Hittorf was first to realize that something must be traveling in straight lines from the cathode to cast the shadows . Eugen Goldstein named them cathode rays . </P> <P> At this time, atoms were the smallest particles known, and were believed to be indivisible . What carried electric currents was a mystery . During the last quarter of the 19th century many experiments were done to determine what cathode rays were . There were two theories . Crookes and Arthur Schuster believed they were particles of "radiant matter," that is, electrically charged atoms . German scientists Eilhard Wiedemann, Heinrich Hertz and Goldstein believed they were "aether waves", some new form of electromagnetic radiation, and were separate from what carried the electric current through the tube . </P> <P> The debate was resolved in 1897 when J.J. Thomson measured the mass of cathode rays, showing they were made of particles, but were around 1800 times lighter than the lightest atom, hydrogen . Therefore, they were not atoms, but a new particle, the first subatomic particle to be discovered, which he originally called "corpuscle" but was later named electron, after particles postulated by George Johnstone Stoney in 1874 . He also showed they were identical with particles given off by photoelectric and radioactive materials . It was quickly recognized that they are the particles that carry electric currents in metal wires, and carry the negative electric charge of the atom . </P>

Where did the term cathode ray come from why is this important