The differential analyser is a mechanical analogue computer designed to solve differential equations by integration, using wheel-and-disc mechanisms to perform the integration. It was one of the first advanced computing devices to be used operationally.
The original machines could not add, but then it was noticed that if the two wheels of a rear differential are turned, the drive shaft will compute the average of the left and right wheels. Addition and subtraction are then achieved by using a simple gear ratio of 1:2; the gear ratio provides multiplication by two, and multiplying the average of two values by two gives their sum. Multiplication is just a special case of integration, namely integrating a constant function.
Ball-and-disc integrator for studying tides.
Kay McNulty, Alyse Snyder, and Sis Stump operate the differential analyser in the basement of the Moore School of Electrical Engineering, University of Pennsylvania, Philadelphia, Pennsylvania, c. 1942–1945.
A differential analyser at the NACA Lewis Flight Propulsion Laboratory, 1951
MOTAT's Meccano differential analyser in use at the Cambridge University Mathematics Laboratory, c. 1937. The person on the right is Dr Maurice Wilkes, who was in charge of it at the time
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A page from the Bombardier's Information File (BIF) that describes the components and controls of the Norden bombsight. It was a highly sophisticated optical/mechanical analog computer used by the United States Army Air Force during World War II, the Korean War, and the Vietnam War to aid the pilot of a bomber aircraft in dropping bombs accurately.
TR-10 desktop analog computer of the late 1960s and early 1970s
The Antikythera mechanism, dating between 150 and 100 BC, was an early analog computer.
Analog computing machine at the Lewis Flight Propulsion Laboratory c. 1949.
