Blackett, Patrick Maynard Stuart (1897-1974)

English physicist

Patrick Maynard Stuart Blackett was a physicist with wide-ranging scientific and personal interests. He is best known for his improvements to the Wilson cloud chamber leading to important discoveries about fundamental particles and cosmic rays. His contributions to the study of magnetism helped confirm continental drift theory . Throughout his career he was admired as an ingenious experimenter. Blackett was involved in British military defense strategies during World War II, but remained an outspoken critic of Western nuclear policies to the end of his life. For his work with the Wilson cloud chamber, Blackett was awarded the 1948 Nobel Prize in physics.

Blackett was born in London, England to Arthur Stuart and Caroline Frances Maynard Blackett. His grandfather had been Anglican vicar of Croydon, Surrey, and his father was a stockbroker. As a child he developed a strong interest in nature, especially birds. Intending a naval career, Blackett attended Osborne Royal Naval College and Dartmouth Royal College. He began active naval duty when World War I broke out in 1914.

After the war, while still in the navy, he studied for six months at Magdalene College, Cambridge. This experience, coupled with his sense that the navy was unlikely to pursue technological innovations, convinced him to pursue a scientific career. He left the service, graduating from Cambridge with a B.A. in physics in 1921. In 1924, Blackett married Costanza Bayon, with whom he had a daughter and a son.

Cambridge's Cavendish Laboratory under Ernest Rutherford's direction was one of the world's foremost centers of theoretical physics after World War I. When Blackett received a fellowship to continue studying there, Rutherford put him to work with the Wilson cloud chamber. A cloud chamber is a device that makes it possible to track the movements of fundamental particles. It consists of a transparent cylinder filled with supersaturated water vapor. The cylinder is set between the poles of an electromagnet. When charged particles are fired into it, the water vapor condenses on the resulting ions and creates trails which can be photographed.

Blackett made improvements to a cloud chamber he inherited from a previous student, and by 1924, was able to confirm Rutherford's prediction that one element could be transmuted into another artificially. By filling the cloud chamber with nitrogen gas and water vapor and bombarding the mixture with alpha particles (helium atoms), Blackett produced a hydrogen atom and an oxygen isotope.

In 1932, Blackett began a productive collaboration studying cosmic rays with the Italian physicist Giuseppe P. S. Occhialini. Cosmic rays were known to reach earth from extraterrestrial sources, but their exact composition was unclear. At the time, very few fundamental particles were postulated, and cosmic rays were thought to be high-energy photons, or light quanta.

Blackett and Occhialini further modified the cloud chamber by combining it with two Geiger counters so that they could obtain more continuous photographs of the particle tracks. After three years and many thousands of photographs, they were able to confirm the existence of the first antimatter particle, the positron, which had been predicted by Carl Anderson. The American physicist Robert A. Millikan had thought this positively charged particle was a proton, but Blackett and Occhialini showed that the particle had the same mass as an electron, and that positrons occurred in "showers" paired with equal numbers of electrons. Blackett also noted a curious high energy component of cosmic rays later found to be the meson.

In 1937, Blackett replaced W. L. Bragg at the University of Manchester and began to build a strong research facility there. With the onset of World War II, he was tapped by the British government to assist in defense measures. He served on the Tizard Committee from 1935 to 1936, and became Director of Naval Operational Research, where he made statistical analyses of the predicted results of differing military strategies.

Blackett, however, opposed Britain's efforts to develop its own nuclear weapons, and though he supported the American bomb project, he was highly critical of Allied nuclear policy during and after the war. He decried the bombing of German civilians and the use of atomic bombs at Hiroshima and Nagasaki. In 1948, his book Military and Political Consequences of Atomic Energy appeared (published in America as Fear, War and the Bomb ). That same year he was also awarded the Nobel Prize, but public hostility to his political views in the climate of the early Cold War overshadowed the acclaim accompanying the prize. Blackett did not return to public service until the election of a Labor government in 1964.

In the late 1940s, Blackett became interested in magnetism and the rotation of massive bodies. The idea that all rotating bodies generate magnetism had been discussed for many years, and if confirmed would have been a major new physical theory. Based on his study of existing observations of the magnetism of the Sun , the earth, and some stars, Blackett thought the hypothesis was plausible. In order to test it, he devised a magnetometer that was ten thousand times more sensitive than any previous such instrument. Ultimately Blackett decided the theory was incorrect, but his interest in geological magnetism continued. He investigated the history of changes in the earth's magnetic field and came to support the theory of continental drift, which postulates that the earth's continents are made of crustal plates that slowly move atop a layer of molten rock (magma ). His magnetometer proved to be very useful in the study of the magnetic fields of small rocks, which eventually helped to confirm continental drift.

In 1965, Blackett became president of the Royal Society, which under his leadership became international in focus. Though he was happy to be welcomed back into the public mainstream, Blackett continued making his political views known, describing himself as a Fabian Socialist and advocating a closer solidarity between scientists and the working class. He also devoted several years to studying scientific, political, and economic conditions in India. Blackett's last academic post was at London's Imperial College of Science and Technology from 1953 to 1965. During his career he received numerous awards in addition to the Nobel Prize, including twenty honorary degrees. In 1969, he was made a life peer, Baron Blackett of Chelsea. Blackett died in London at the age of 76.

See also Continental shelf; Quantum theory and mechanics