In 1897, a British physicist named J. J. Thomson discovered electrons through his cathode ray experiments. Thomson made these cathode rays by firing electrical currents through glass pipes filled with low-density gas. Thomson measured the ratio of the mass of the cathode ray to its electrical charge. What he found was that the ratio was always the same, regardless of what elemental gas was in the pipe. These results indicated that the current inside the cathode ray tube was made of tiny particles that carried a negative charge -- he named these particles electrons. Since the mass to charge ratio was the same no matter what gas he used inside the glass tube, Thomson reasoned that electrons must be common to all atoms, and that all electrons must be the same.
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