Electrons in gases and vacuum
It was known to the scientists of the eighteenth century that the succession of sparks from an electric machine changed to a quiet luminous discharge when the pressure of the surrounding air was reduced. One of the investigators of this phenomenon was a Fellow of the Royal Society named William Watson, who, in 1750, produced a luminous electric discharge between two brass rods at the opposite ends of an evacuated glass tube, about a metre long. Also Lord Charles Cavendish, father of the eccentric Henry Cavendish, showed that a similar discharge could be sent through the Toricellian vacuum at the top of a barometer tube.
About the middle of the nineteenth century an expert glass-blower named Geissler obtained some remarkably beautiful coloured discharges by using other gases besides air, contained in skilfully shaped tubes in a variety of patterns. Sometimes these tubes were rotated like Catherine-wheels and their colours were further enhanced by the use of glass containing various minerals which fluoresced brilliantly while the discharge was passing.