Thomson next measured for different cathode materials. Finding them all to be the same, he concluded that all metals emit the same cathode rays. Thomson then compared his result to the charge-to-mass ratio of the hydrogen ion, known from electrolysis to have a value of . This value was roughly 1000 times smaller than for the cathode-ray particles, which could imply that a cathode-ray particle has a much larger charge than a hydrogen ion, or a much smaller mass, or some combination of these.
Electrolysis experiments suggested the existence of a basic unit of charge, so it was tempting to assume that the cathode-ray charge was the same as the charge of a hydrogen ion. However, cathode rays were so different from the hydrogen ion that such an assumption could not be justified without some other evidence. To provide that evidence, Thomson called attention to previous experiments showing that cathode rays can penetrate thin metal foils but atoms cannot. This can be true, Thomson argued, only if cathode-ray particles are vastly smaller and thus much less massive than atoms.
In a paper published in 1897, Thomson assembled all of the evidence to announce the discovery that cathode rays are negatively charged particles, that they are much less massive than atoms, and that they are identical when generated by different elements. In other words, Thomson had discovered a subatomic particle, one of the constituents of which atoms themselves are constructed. In recognition of the role this particle plays in electricity, it was later named the electron.