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A Geissler tube is a precursor to modern gas discharge tubes, demonstrating the principles of electrical glow discharge, akin to contemporary neon lights, and central to the discovery of the electron.[1]: 67 This device was developed in 1857 by Heinrich Geissler, a German physicist and glassblower. A Geissler tube is composed of a sealed glass cylinder of various shapes, which is partially evacuated and equipped with a metal electrode at each end. It contains rarefied gases—such as neon or argon, air, mercury vapor, or other conductive substances, and sometimes ionizable minerals or metals like sodium. When a high voltage is applied between the electrodes, there is an electric current through the tube, causing gas molecules to ionize by shedding electrons. The free electrons reunite with the ions and the resulting energic atoms emit light via fluorescence, with the emitted color characteristic of the contained material.
Colorful decorative Geissler tubes were made in many artistic designs around the turn of the century, to demonstrate the new technology of electricity. Simple straight ones were used as high voltage sensors in physics experiments. The technology of gas-discharge lighting pioneered in Geissler tubes evolved around 1910 into commercial neon lighting, seen today.