William Crookes

William Crookes (1832–1919) was a British chemist and physicist who discovered thallium, investigated cathode rays, and invented the Crookes radiometer.

Thallium: A soft, highly toxic metallic element discovered by William Crookes in 1861 through its distinctive green spectral line. Crookes identified this element by spectroscopy while examining residues from selenium production.
Crookes tube: An evacuated glass tube in which electrical discharge produces cathode rays. Crookes designed improved tubes to study the behavior of cathode rays at low gas pressures.
Royal College of Chemistry: A London institution founded in 1845 to teach and advance chemical science. Crookes studied chemistry there before establishing himself as an independent investigator.
J. J. Thomson: An English physicist who identified the electron in 1897 through experiments with cathode rays. Thomson resolved the nature of the rays Crookes had investigated in discharge tubes.
Spiritualism: A nineteenth-century religious movement centered on communication with the spirits of the dead. Crookes’s investigations of mediums brought this movement into direct contact with laboratory science.
Cathode ray: A stream of electrons emitted from a cathode in a sufficiently evacuated tube. Crookes’s experiments made these rays central to investigations of electrical discharge in gases.
Radiation pressure: The pressure exerted by electromagnetic radiation when it transfers momentum to a surface. Crookes investigated whether light’s pressure could explain the motion of his radiometer vanes.
August Wilhelm von Hofmann: A German chemist known for research on organic compounds and for teaching in Britain and Germany. Hofmann taught Crookes at the Royal College of Chemistry and influenced his early scientific training.
Oliver Lodge: A British physicist who studied electrical waves and contributed to the development of radio technology. Lodge participated in late Victorian debates about Crookes’s ideas on matter and radiation.
Daniel Dunglas Home: A Scottish spiritualist medium known for public séances in nineteenth-century Europe. Crookes investigated Home’s reported phenomena and defended some observations as genuine.

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