The Geissler Tube is a sealed glass cylinder of a unique design with a metal electrode at each end. The Geissler Tube was invented by the German glassblower and physicist, Johann Heinrich Wilhelm Geissler (1814-1879) in 1857. Geissler tubes were the first gas discharge tubes. Each contains rarefied gasses such as neon or argon; conductive fluids; or ionizable minerals or metals. When voltage is applied to the apparatus, electric current flows through the tube causing its contents to fluoresce. A multitude of colors and effects can be achieved by modifying the gaseous contents of the tube. Geissler tubes were mass-produced beginning in the 1880s as novelty and entertainment devices. By the early 20th century, the technology was commercialized and evolved into neon lighting.