Bush, Vannevar (1890–1974)

US electrical engineer and scientist. During the 1920s and 1930s he developed several mechanical and mechanical–electrical analogue computers which were highly effective in the solution of differential equations. The standard electricity meter is based on one of his designs.

Bush was born in Everett, Massachusetts, and studied at Tufts College and the Massachusetts Institute of Technology (MIT). From 1932 he held senior positions at MIT. During World War I he worked on a magnetic device for detecting submarines. During World War II, as scientific adviser to President F D Roosevelt, Bush was one of the initiators of the atomic-bomb project. After the war he took part in the setting-up and running of the Office of Scientific Research and Development and its successor, the Research and Development Board.

Early inventions In about 1925 Bush began to construct what he called the product integraph. It contained a linkage to form the product of two algebraic functions and represent it mechanically. He also devised a watt-hour meter, a direct ancestor of the electricity meter, which integrated the product of electric current and voltage. By similarly using current and voltage to represent equations, his machine was able to evaluate integrals involved in the solution of differential equations.

The product integraph was limited to the solution of first-order differential equations. To build a device capable of the solution of second-order equations, Bush coupled one of the watt-hour meters to a mechanical device known as a Kelvin integrator.

Towards the computer In 1930 Bush began work on an almost totally mechanical machine known as the differential analyser. This had six integrators, three input tables, and an output table, which showed the graphical solution of an equation. It could handle 18 independent variables and is recognized as one of the most important forerunners of the electronic analogue computer.

Bush built several analysers designed to solve specific problems, and another large analyser, which had many of the operations electrified and a tape input that reduced the time taken for setting up a problem from days to minutes.

One of Bush's other inventions was a cipher-breaking machine, which played a large part in breaking Japanese codes during World War II.