SHEILA TERRY / SCIENCE PHOTO LIBRARY SHEILA TERRY / SCIENCE PHOTO LIBRARY
This was the cutting-edge physics of the day, with electric currents used to make gases glow in vacuum tubes (Geissler tubes), made possible by the development of an improved vacuum pump by Heinrich Geissler in around 1855 (this would later form the basis of neon lights). In 1859, Julius Plucker used a Geissler tube to observe cathode rays. From 1875, William Crookes developed the Crookes tube (far left, with Maltese Cross shadow). The glowing gases and cathode rays were explained by the discovery of the electron by J.J. Thomson in 1897, six years after this artwork appeared in Physique Populaire (E.Desbeaux, 1891).
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