The Electron & Edison Effect

Thomson identifies the electron; Millikan measures its charge.

Late-nineteenth-century experiments showed that cathode rays were streams of particles much smaller than atoms. Sir J. J. Thomson identified the electron and measured its charge-to-mass ratio. Robert Millikan's oil-drop work later determined the elementary charge with high precision, making the particle description quantitative.

Electronics could now be defined around the emission, behaviour and control of electrons rather than only around bulk electrical conduction.

A hot filament sends charge across empty space.

Thomas Edison observed a bluish glow in some early lamps and found that current could flow from a hot filament toward a second electrode when that electrode was positive relative to the filament. The evacuated bulb contained no ordinary metallic bridge between them.

Heating supplied electrons at the emitter with enough energy to escape the material's surface—a process later called thermionic emission. A positive plate collected the emitted electrons; a negative plate repelled them. The effect was directional and therefore already contained the principle of a valve.

Controlled emission separates electronics from electricity alone.

Fleming converted the effect into a two-electrode rectifier for radio detection. Coolidge improved electron tubes for X-ray production. De Forest added a control grid and made amplification practical. The common idea was the same: emit electrons, shape their path with electric fields and collect them at an electrode.