Electron streams in discharge tubes
Applying voltage within a low-pressure tube containing electrodes can produce a charged-particle stream associated with the cathode. Fluorescence and detectors reveal its effects. The historical term ray does not identify it as ordinary light: the stream consists of electrons whose behaviour can be experimentally investigated.
Deflection by electrical and magnetic fields
Electric and magnetic fields deflect charged electrons in ways related to their charge, speed and mass. Fields can be arranged so opposing effects balance. Interpreting the result requires field strengths and geometry; a fluorescent trace alone does not directly reveal every physical parameter of the particles.
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A particle common to different materials
Thomson compared different cathode materials and gases and found a common charge-to-mass relationship. His 1897 work identified cathode rays with electrons and connected them with atomic composition. The evidence for smaller charged constituents of atoms emerged from comparable measurements across several experimental conditions.
From observed rays to controlled beams
Separating electron production, acceleration and deflection turned discharge-tube studies into a platform for controlled beams. Changing electrodes and fields adjusts where electrons arrive or how matter responds. These methods linked atomic-structure questions with electron optics and expanded the range of phenomena accessible to experimental measurement.