Glowing Geissler tubes, 1858.
© Science Museum / Science & Society Picture Library
Illustration showing electric discharges through gases, from 'Beobachtungen uber das geschichtete electrische Licht' (Observations on the history of electric light) by W H Theodor Meyer, published in 1858. In this pamphlet, Meyer discuses the phenomena associated with Geissler tubes, in which a high-voltage electric current is passed through a gas at a pressure much lower than that of the atmosphere, producing a fascinating glow as the gas is ionised. The tubes are named after Heinrich Geissler (1815-1879), a Bonn glassblower who devised a new pump that produced a much better vacuum than ever before. In 1855 Geissler used the pump to evacuate intricately shaped glass tubes in order to demonstrate this colourful electrical effect.