Electrical engineer Charles D. Fawcett setting the initial conditions on a differential analyzer¹ programmed to integrate van der Pol's differential equation² (March 6, 1935). This analog computer was built in the basement of the Moore School of Electrical Engineering³ at the University of Pennsylvania and was used extensively in the computation of artillery firing tables prior to the invention of the ENIAC⁴ digital computer, which, in many ways, was modeled on this machine. A differential analyzer is a mechanical analog 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. The Moore School is particularly famed as the birthplace of the computer industry.
Rice Fields
Sapa, Vietnam
