Crookes

William Crookes (1832–1919) was an English chemist and physicist known for his work in spectroscopy, radiometry, and the study of cathode rays. In 1861 he identified a new element, thallium, by examining spectral lines; he named the element after the Greek word thallos, meaning green shoot.

Crookes conducted extensive experiments with cathode rays using a variety of high-vacuum tubes, culminating in the experimental apparatus later known as the Crookes tube. These studies helped establish the existence of cathode rays and influenced later work on electron theory, most notably by J. J. Thomson.

Additionally, he invented the radiometer, often called the Crookes radiometer, in the 1870s. The device features a set of vanes that spin when exposed to light or radiant energy, and it provided a platform for investigations into radiative heat and gas dynamics, though the mechanism is more complex than a simple light pressure.

Crookes held prominent positions in the scientific community, was a fellow of the Royal Society, and contributed to scientific literature and education.

Later in his life, he engaged in psychical research, studying mediums and phenomena associated with spiritualism. While these investigations were influential in popular culture at the time, they have been viewed skeptically by the scientific establishment.