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Douglas Hartree

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Douglas Rayner Hartree was an influential English mathematician and physicist. He lived from 1897 to 1958. His work bridged the gap between theoretical science and practical calculation. He is most recognized for his contributions to numerical analysis. This field focuses on using mathematical algorithms to find approximate solutions to complex problems. Hartree applied these methods to atomic physics and the development of early computing machines. His career spanned significant global events, including both World Wars.

During the First World War, Hartree worked on anti-aircraft ballistics. He worked under A. V. Hill alongside his father and brother. This experience sparked a lifelong interest in practical calculation and numerical methods. He learned to solve differential equations using only pencil and paper. During this time, he improvised a long-base height-finder using wires, posts, and steel tape. This device became known as the Hartree height-finder. British Anti-Aircraft troops used it extensively because it was cheap and easy to manufacture. It allowed users to calculate height rapidly using simple arithmetic.

After the war, Hartree turned his attention to the structure of the atom. A visit from Niels Bohr in 1921 inspired him to apply numerical skills to atomic theory. He earned his PhD in 1926 under the supervision of Ernest Rutherford. Hartree used his knowledge of differential equations to study the quantum theory of atoms. He derived the Hartree equations to describe how electrons are distributed within an atom. He also proposed the self-consistent field method to solve these equations. While his original wavefunctions did not satisfy the Pauli exclusion principle, his work laid a vital foundation. Later, V. Fock published equations that included exchange effects, resulting in the Hartree–Fock equations. These equations remain essential in modern computational chemistry and density functional theory.

In 1929, Hartree became the Beyer Chair of Applied Mathematics at the University of Manchester. He was a pioneer in mechanical computing. In 1933, he visited Vannevar Bush at the Massachusetts Institute of Technology. There, he studied a machine called a differential analyser. Upon returning to Manchester, he built his own version using Meccano parts.

Analyseur différentiel de Douglas Hartree
Analyseur différentiel de Douglas Hartree

He later secured funding to build a more robust machine with Metropolitan-Vickers. He used this machine to calculate timetables for the London, Midland and Scottish Railway. He also applied it to fluid dynamics and control theory.

During the Second World War, Hartree managed two distinct computing groups. The first group worked on solving differential equations for the Ministry of Supply. This group handled diverse problems like underwater explosions, heat flow in steel, and radio propagation. The second group focused on magnetron research to assist in the development of radar. Because the university had only one large differential analyser, Hartree organized his group to work in parallel. He had members use mechanical desk calculators as if they were three separate central processing units, or CPUs. This allowed them to simulate classical particle movements to solve complex problems.

Hartree was also a key figure in the transition to electronic computing. In 1946, he traveled to the United States to evaluate the ENIAC computer. He became the first civilian to program this massive machine. He used it to study the flow of compressible fluids over surfaces.

Analyseur différentiel de Douglas Hartree
Analyseur différentiel de Douglas Hartree

His observations helped shape the future of computing in Britain. He briefed Maurice Wilkes on the capabilities of ENIAC, which influenced the design of the EDSAC computer. Hartree also recommended that the Royal Society fund the construction of a general-purpose computer at the University of Manchester. His advocacy was successful, helping to launch Manchester's computing developments.

Hartree possessed a profound vision for the impact of computing technology. In a 1946 interview, he noted that machines could make certain human activities 1,000 times faster. He compared the potential speed of a computer to traveling from London to Cambridge in just five seconds. He predicted that computers would eventually tackle massive problems in economics, medicine, and sociology. He understood that the sheer load of computing required for these fields was currently a barrier to progress. His work helped break those barriers, moving science into the digital age.

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