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AGeissler tube is a precursor to moderngas discharge tubes, demonstrating the principles of electricalglow discharge, akin to contemporaryneon lights, and central to the discovery of theelectron.[1]: 67 This device was developed in 1857 byHeinrich Geissler, a German physicist and glassblower. A Geissler tube is composed of a sealed glass cylinder of various shapes, which is partiallyevacuated and equipped with a metalelectrode at each end. It contains rarefied gases—such asneon orargon,air,mercury vapor, or otherconductive substances, and sometimesionizable minerals or metals likesodium. When ahigh voltage is applied between the electrodes, there is anelectric current through the tube, causing gas molecules toionize by sheddingelectrons. The free electrons reunite with theions and the resulting energic atoms emit light viafluorescence, 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 commercialneon lighting, seen today.
Geissler tubes were mass-produced from the 1880s as novelty and entertainment devices, with various spherical chambers and decorative serpentine paths formed into the glass tube. Some tubes were very elaborate and complex in shape and would contain chambers within an outer casing. A novel effect could be obtained by spinning a glowing tube at high speed with a motor; a disk of color was seen due topersistence of vision. When an operating tube was touched by the hand, the shape of the glowing discharge inside often changed due to the capacitance of the body.
Simple straight Geissler tubes were used in early-20th-century scientific research as high voltage indicators. When a Geissler tube was brought near a source of high voltage, alternating current, such as aTesla coil orRuhmkorff coil, it would light up even without contact with the circuit. They were used to tune thetank circuits ofradio transmitters to resonance. Another example of their use was to findnodes ofstanding waves ontransmission lines, such asLecher lines used to measure the frequency of early radio transmitters.
Another use around 1900 was as the light source in Pulfrichrefractometers.[2]
Geissler tubes are sometimes still used in physics education to demonstrate the principles ofgas discharge tubes.
Geissler tubes were the firstgas discharge tubes, and have had a large impact on the development of many instruments and devices which depend on electric discharge through gases.[1]: 67
One of the most significant consequences of Geissler tube technology was the discovery of theelectron and the invention of electronicvacuum tubes. By the 1870s better vacuum pumps enabled scientists to evacuate Geissler tubes to a higher vacuum; these were calledCrookes tubes afterWilliam Crookes. When current was applied, it was found that the glass envelope of these tubes would glow at the end opposite to the cathode. Observing that sharp-edged shadows were cast on the glowing tube wall by obstructions in the tube in front of the cathode,Johann Hittorf realized that the glow was caused by some type of ray travelling in straight lines through the tube from the cathode. These were namedcathode rays. In 1897J. J. Thomson showed that cathode rays consisted of a previously unknown particle, which was named theelectron. The technology of controlling electron beams resulted in the invention of the amplifyingvacuum tube in 1907, which created the field ofelectronics and dominated it for 50 years, and thecathode-ray tube which was used inradar andtelevision displays.
Some of the devices which evolved from Geissler tube technology:
