Although at the time of Millikan's oil-drop experiments it was becoming clear that there exist such things as subatomic particles, not everyone was convinced. Experimenting with cathode rays in 1897, J. J. Thomson had discovered negatively charged 'corpuscles', as he called them, with a charge-to-mass ratio 1840 times that of a hydrogen ion. Similar results had been found by George FitzGerald and Walter Kaufmann. Most of what was then known about electricity and magnetism could be explained on the basis that charge is a continuous variable. This in much the same way that many of the properties of light can be explained by treating it as a continuous wave rather than as a stream of photons.