William Crookes
Background
William Crookes was born June 17, 1832 in London, England, and died on April 4, 1919. He was a British chemist and physicist. William discovered the element thallium and the invention of "Crookes's tubes", as well as the radiometer.
Crookes tube - Video Learning - WizScience.com
Crookes's Tube
These tubes were filled with matter known as the "fourth state", meaning the free path of the molecules are large; these tubes are now called "Crookes's tubes".
Element Thallium
William Crookes's most notable discovery was the element Thallium when he observed a green line in the spectrum of selenium
Radiometer
After the discovery of Thallium this lead to the construction of the Radiometer.