The Geissler tube is a glass tube for emonstrating the principles of electrical glow discharge. The tube was invented by the German physicist and glassblower Heinrich Geissler in 1857. The Geissler tube was an evacuated glass cylinder with an electrode at each end. Geissler tubes contain a combination of one of the following: rarefied (thinned) gasses such as neon, argon, or air, or conductive liquids or minerals. When a high voltage is applied to the terminals an electrical current flows through the tube. The current will disassociate electrons from the gas molecules, creating ions and when electrons recombine with the ions different lighting effects are created. The light will be characteristic of the material contained within the tube and will be composed of one or more narrow spectral lines.