  Strong evidence for the charged and massive particles assumed in an atomic explanation of electrolysis and radiation was provided by the experiments on cathode rays performed by J. J. Thomson (1897). The experimental facts involving cathode rays could be explained on the assumption that they were beams of charged particles each with the same value for the ratio of their charge to their mass. Thomson’s experiments enabled that ratio to be measured. A range of other experiments in the ensuing few years, especially by Milliken, enabled the charge on the cathode particles, electrons, to be estimated, and this led to a mass of the electron very much smaller than that of atoms. The fact that identical electrons were emitted from cathodes of a range of materials under a range of conditions strongly suggested that the electron is a fundamental constituent of all atoms.