Crookes made a career of being a meteorologist and fierce lecturer for multiple studies and courses. Crookes worked in chemistry and physics. His experiments were notable for the originality of their design. He executed them skillfully. His interests, ranging over pure and applied science, economic and practical problems, and psychiatric research, made him a well-known personality. He received many public and academic honours. Crookes's life was one of unbroken scientific activity.
William Crookes (later Sir William Crookes) was born in London, the eldest of 16 siblings. His father, Joseph Crookes, was a tailor of north-country origin, at that time living with his second wife, Mary Scott Lewis Rutherford Johnson.
From 1850 to 1854 he filled the position of assistant in the college, and soon embarked upon original work. It wasn't in organic chemistry which the focus of his teacher,
August Wilhelm von Hofmann, might have been expected to lead him towards, but into new compounds of
selenium. These were the subject of his first published papers, 1851. He worked with
Manuel Johnson at the
Radcliffe Observatory in
Oxford in 1854, where he adapted the recent innovation of
wax paper photography to machines built by
Francis Ronalds to
continuously record meteorological parameters.
 In 1855 he was appointed lecturer in chemistry at the
Chester Diocesan Training College.
In 1856 he married Ellen, daughter of William Humphrey of Darlington.
 They had three sons and a daughter. Married and living in London, he was devoted mainly to independent work. In 1859, he founded the
Chemical News, a science magazine which he edited for many years and conducted on much less formal lines than was usual for the journals of scientific societies.
Blue plaque, 7 Kensington Park Gardens, London
In 1861, Crookes discovered a previously unknown element with a bright green emission line in its spectrum and named the element
thallium, from the Greek thallos, a green shoot. Crookes wrote a standard treatise on Select Methods in Chemical Analysis in 1871. Crookes was effective in experimentation. The method of
spectral analysis, introduced by
Kirchhoff, was received by Crookes with great enthusiasm and to great effect. His first important discovery was that of the element thallium, announced in 1861, and made with the help of spectroscopy. By this work his reputation became firmly established, and he was elected a fellow of the Royal Society in 1863.
He developed the
cathode rays. He published numerous papers on
spectroscopy and conducted research on a variety of minor subjects. In his investigations of the conduction of electricity in low pressure gases, he discovered that as the pressure was lowered, the negative electrode (cathode) appeared to emit rays (the so-called "cathode rays", now known to be a stream of
free electrons, and used in
cathode ray display devices). As these examples indicate, he was a pioneer in the construction and use of
vacuum tubes for the study of physical phenomena.
 He was, as a consequence, one of the first scientists to investigate what is now called a
plasma and identified it as the fourth state of matter in 1879.
 He also devised one of the first instruments for studying nuclear radioactivity, the
Crookes investigated the properties of
cathode rays, showing that they travel in straight lines, cause
fluorescence when they fall on some substances, and that their impact can produce great heat. He believed that he had discovered a fourth state of matter, which he called "radiant matter",
 but his theoretical views on the nature of "radiant matter" were to be superseded.
 He believed the rays to consist of streams of particles of ordinary molecular magnitude. It remained for Sir
J. J. Thomson to expound on the subatomic nature of cathode rays (consisting of streams of negative
). Nevertheless, Crookes's experimental work in this field was the foundation of discoveries which eventually changed the whole of chemistry and physics.
Crookes' attention had been attracted to the vacuum balance in the course of his research into thallium. He soon discovered the phenomenon which drives the movement in a
Crookes radiometer, in which a set of vanes, each blackened on one side and polished on the other, rotate when exposed to radiant energy. Crookes did not, however, provide the true explanation of this apparent "attraction and repulsion resulting from
After 1880, he lived at 7
Kensington Park Gardens where all his later work was done, in his private laboratory.
Crookes identified the first known sample of
helium, in 1895. Crookes was knighted in 1897.
In 1903, Crookes turned his attention to the newly discovered phenomenon of
radioactivity, achieving the separation from
uranium of its active transformation product, uranium-X (later established to be
protactinium). Crookes observed the gradual
decay of the separated transformation product, and the simultaneous reproduction of a fresh supply in the original uranium. At about the same time as this important discovery, he observed that when "p-particles", ejected from radio-active substances, impinge upon
zinc sulfide, each impact is accompanied by a minute scintillation, an observation which forms the basis of one of the most useful methods in the technique of radioactivity.