Working Geissler tube, c 1988.
© Science Museum / Science & Society Picture Library
The German glass blower Hermann Geissler (1814-1879) produced the first permanently sealed discharge tubes to show that when an electric current passes through a gas at low pressure the gas glows. These were the fore- runners of the Geisler tubes used in science demonstrations. Two metal electrodes pas through the glass, and are connected to a very high voltage to make the gas in it glow. The colour produced is characteristic of the gas. The tubes may have two or more chambers containing different gases to produce different colours.