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Differential Analyzer

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Differential Analyzer

This article is about analogue differential analysers. For the digital implementation, see Digital Differential Analyzer.

The differential analyser is a mechanical working.


Research on solutions for differential equations using mechanical devices, discounting planimeters, started at least as early as 1836, when the French physicist Gaspard-Gustave Coriolis designed a mechanical device to integrate differential equations of the first order.[3]

The first description of a device which could integrate differential equations of any order was published in 1876 by James Thomson, who was born in Belfast in 1822, but lived in Scotland from the age of 10.[4] Though Thomson called his device an "integrating machine", it is his description of the device, together with the additional publication in 1876 of two further descriptions by his younger brother, Lord Kelvin, which represents the invention of the differential analyser.[5]

On Lord Kelvin's advice, Thomson's integrating machine was incorporated into a fire-control system for naval gunnery being developed by Arthur Pollen, resulting in an electrically driven, mechanical analogue computer, which was completed by about 1912.[6] Italian mathematician Ernesto Pascal also developed integraphs for the mechanical integration of differential equations and published details in 1914.[7] However, the first widely practical differential analyser was constructed by Harold Locke Hazen and Vannevar Bush at MIT, 1928–1931, comprising six mechanical integrators.[8][9][10] In the same year, Bush described this machine in a journal article as a "continuous integraph".[11] When he published a further article on the device in 1931, he called it a "differential analyzer".[12] In this article, Bush stated that "[the] present device incorporates the same basic idea of interconnection of integrating units as did [Lord Kelvin's]. In detail, however, there is little resemblance to the earlier model." According to his 1970 autobiography, Bush was "unaware of Kelvin’s work until after the first differential analyzer was operational."[13] Claude Shannon was hired as a research assistant in 1936 to run the differential analyzer in Bush's lab.[14]

Douglas Hartree of Manchester University brought Bush's design to England, where he constructed his first "proof of concept" model with his student, Arthur Porter, during 1934: as a result of this, the university acquired a full scale machine incorporating four mechanical integrators in March 1935, which was built by Metropolitan-Vickers, and was, according to Hartree, "[the] first machine of its kind in operation outside the United States".[15] During the next five years three more were added, at Cambridge University, Queen's University Belfast, and the Royal Aircraft Establishment in Farnborough.[16] One of integrators from this proof of concept is on display in the History of Computing section of the Science Museum (London) alongside a complete Manchester machine.

In Norway, the locally built Oslo Analyser was finished during 1938, based on the same principles as the MIT machine. This machine had 12 integrators, and was the largest analyser built for a period of four years.[17]

In the United States, further differential analysers were built at the Ballistic Research Laboratory in Maryland and in the basement of the Moore School of Electrical Engineering at the University of Pennsylvania during the early 1940s.[18] The latter was used extensively in the computation of artillery firing tables prior to the invention of the ENIAC, which, in many ways, was modelled on the differential analyser.[19] Also in the early 1940s, with Samuel H. Caldwell, one of the initial contributors during the early 1930s, Bush attempted an electrical, rather than mechanical, variation, but the digital computer built elsewhere had much greater promise and the project ceased.[20] In 1947, UCLA installed a differential analyser built for them by General Electric at a cost of $125,000.[21] By 1950, this machine had been joined by three more.[22]

In Canada, a differential analyser was constructed at the University of Toronto in 1948 by Beatrice Helen Worsley, but it appears to have had little or no use.[23]

A differential analyser may have been used in the development of the bouncing bomb, used to attack German hydroelectric dams during World War II.[24] Differential analysers have also been used in the calculation of soil erosion by river control authorities.

The differential analyser was eventually rendered obsolete by electronic analogue computers and, later, digital computers.

Use of Meccano

The model differential analyser built at Manchester University in 1934 by Douglas Hartree and Arthur Porter made extensive use of Meccano parts: this meant that the machine was cheaper to build, and it proved "accurate enough for the solution of many scientific problems".[25] A similar machine built by J.B. Bratt at Cambridge University in 1935 is now in the Museum of Transport and Technology (MOTAT) collection in Auckland, New Zealand.[25] A memorandum written for the British military's Armament Research Department in 1944 describes how this machine had been modified during World War II for improved reliability and enhanced capability, and identifies its wartime applications as including research on the flow of heat, explosive detonations, and simulations of transmission lines.[26] In 1948, this machine was bought by Professor Harry Whale of Auckland, for 100 pounds sterling, and he then took it to Auckland for use at the Seagrave Radio Research Centre.[27]

It is estimated that "about 15 Meccano model Differential Analysers were built for serious work by scientists and researchers around the world".[28] More recently, building differential analysers with Meccano parts has become a popular project among serious Meccano hobbyists. An example is the differential analyser built at Marshall University, which is now used for educational purposes, in that a student not only solves a differential equation but also becomes the "calculator" by operating the machine, and so develops a better understanding of what a differential equation is.[29]

Cultural references

A differential analyser at UCLA is shown in operation in the 1951 film When Worlds Collide and the 1956 film Earth vs. the Flying Saucers.[21] After UCLA's machines were retired, one was donated to the Smithsonian Institution.[22]



  • Worsley, Beatrice Helen (1947). A mathematical survey of computing devices with an appendix on an error analysis of differential analyzers (Master's Thesis, MIT).
  • Crank, J. (1947). The Differential Analyser, London: Longmans, Green (this is the only book that describes how to set up and operate a mechanical differential analyser).
  • MacNee, A.B. (1948). RLE, Technical Report 90, MIT. Note that this paper describes a very early electronic analogue computer, not a mechanical differential analyser: it is included because the author clearly felt that the only way to introduce such an innovation was to describe it as an "electronic differential analyser").

External links

  • Vannevar Bush bio which focuses on the Differential Analyzer
  • The Differential Analyser Explained (updated July 2009)
  • Tim Robinson's Meccano Differential Analyser
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