William Crookes

WILLIAM CROOKES
1832-1919

English chemist and physicist; His investigations of the photographic process in the 1850s motivated his work in the new science of spectroscopy. Using its techniques, Crooks discovered (1861) the element thallium, which won him election to the Royal Society. His efforts in determining the weight of thalium in an evacuated chamber led to his research in vacuum physics.

Crooks invented the radiometer in 1875 and, beginning in 1878, investigated electrical discharges through highly evaculated "Crookes tubes." These studies laid the foundation for J. J. Thomson's research in the late 1890's concerning discharge-tube phenomena. At the age of 68, Crookes began investigating the phenomenon of radioactivity, which had been discovered in 1896, and invented a device that detected alpha particles emitted from radioactive material. Crookes maintained an interest in agriculture and warned in 1898 that the world's population would face starvation unless new fertilizer sources were discovered. He was also interested in psychic phenomena. He was knighted in 1897.

The English physicist William Crookes (1832-1919) had devised, by 1875, a still better evacuated tube (a Crookes tube), in which the electric current through a vacuum could more easily be studied. It seemed quite clear that the electric current started at the cathode and traveled to the anode, where it struck the neighboring glass and created the glow of light. Crookes demonstrated this by placing a piece of metal in the tube and showing that it cast a shadow on the glass on the side opposite the cathode. (The electrical experimenters of the eighteenth and nineteenth centuries, beginning with Benjamin Franklin, had assumed that the current flowed from the concentration arbitrarily named positive to that named negative. Crookes had now shown that, in actual fact, the assumption was wrong and that the flow was from negative to positive.)