William Crookes Biography

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World of Scientific Discovery on William Crookes

Crookes is known as one of the most accomplished experimental physicists of his time. Among his discoveries are the element thallium as well as the cathode-ray tube.

The eldest child of sixteen born to a wealthy London businessman, Crookes was given ample opportunity to pursue his education. At age sixteen he entered the Royal College of Chemistry, studying under August Wilhelm von Hofmann (1818-1892) and eventually serving as his personal assistant. While a student Crookes became an accomplished organic chemist, publishing several papers; however, while attending a meeting at the Royal Institution he met the physicist Michael Faraday, who convinced him to switch his specialty to physics, and particularly to optics and spectroscopy.

After graduating from the Royal College of Chemistry in 1854, Crookes briefly held two academic positions, both of which he found very unsatisfying. After two years of lecturing he received a sizable inheritance from his father's estate, a fortune large enough for Crookes to quit his teaching position and establish his own laboratory. His first project was in the newly emerging field of spectroscopy; he studied the samples of selenium and other materials that remained in his possession from his career as a chemist. While studying the spectral patterns of these compounds he noticed a bright green line that belonged to no other known element; after several years he succeeded in isolating the element, which he named thallium (from the Greek word thallos, meaning "green twig "). At the same time, the French scientist C. A. Lamy had also isolated a sample of thallium, sparking a small controversy over priority. Today, the discovery is usually credited to Crookes.

While studying his new element, Crookes began experimenting with vacuum tubes. He had found that when a small amount of material was weighed upon a scale encased in a vacuum tube, a much more precise measurement could be obtained. However, he also noted that the objects within the tube were occasionally pushed by an invisible force, particularly when exposed to sunlight. To demonstrate this phenomenon Crookes constructed his radiometer, a device consisting of four small vanes balanced upon a pin and sealed within a vacuum tube. Each vane had two sides--one painted black, the other silver. As light struck the radiometer the vanes would turn, as if something were pushing against the black sides. Crookes himself did not know why the device worked. It was not until years later that James Clerk Maxwell used the radiometer as proof for the kinetic theory of gases in which he explained that the tiny particles of air that still remained within the " vacuum" tube were excited by sunlight and exerted pressure against the black vanes, thus turning the system.

Crookes's most important work stemmed from his experiments with vacuum tubes. At that time a great deal of research was being done on cathode rays; Heinrich Geissler (1815-1879) had invented an improved vacuum tube in which two electrodes could be placed, one at each end. An electrical current was sent through the system, and as the air in the tube was evacuated, it would begin to glow. Crookes made further improvements to the system, installing a small pivoting vane within the tube; as the electrical current flowed and the tube was evacuated, the vane would turn slightly, proving the existence of a stream of particles moving from one electrode to the other. Again, Crookes himself could not explain just what these particles were, and it was up to Joseph J. Thomson to demonstrate that cathode rays are streams of particles called electrons.

Though Crookes was knighted in 1897 and received a number of scientific accolades, he was not always well respected by his peers--primarily because of his belief in spiritualism and the occult. He published several papers supporting the validity of psychic research and mediums.