The First Vacuum Tube

Improved vacuum pumps were one of the spin-offs of the railway revolution: the discovery of X-rays and the arrival of "post steam" technology depended on this apparently mundane fact. When the pioneers passed electric current through gases at lower and even lower pressures, a rich variety of effects occurred. First William Crookes noticed that the nature of the colored lights changed as the pressure was reduced. In these circumstances the atoms in the gas emitted light much as the Aurora Borealis or "Northern Lights" are stimulated by electrically-charged high energy particles, cosmic rays, hitting the upper atmosphere. The high atmosphere is rarefied, and vacuum technology produces a similar thin gas in the Crookes tubes. The ghostly shimmer of the aurora in a glass tube is eerie even when you know what it is and to Victorian scientists working in the dark, in all senses of the phrase, it was unnerving. Crookes had become involved with spiritualism following the death of his brother. Seeking a scientific proof of the soul, he became obsessed by the subtle lights in his tubes. Convinced that during seances he had seen "luminous green clouds" and that the lights in the tube were the same as these phantoms, he announced that he had produced ectoplasm.