photo #5088028

Nordsieck’s Differential Analyzer (1950) American theoretical physicist Arnold Nordsieck built this analog computer at the University of Illinois from $700 worth of surplus electronic parts left over from World War II. It was modeled on the mechanical differential analyzers built since the 1930s but with a key difference, it used electrical connections instead of mechanical shafts. Nordsieck’s differential analyzer used synchros (selsyn motors) a type of transformer whose primary-to-secondary coupling may be varied by physically changing the relative orientation of the two windings. These were used to convert angular motion of the disk-and-wheel integrators to electric current. Also visible are the two plotting tables that can be used for input or output. His electromechanical differential analyzer, like mechanical analyzers that preceded it, solved differential equations, thus providing a powerful tool for engineering, rocketry, physics, and other disciplines that needed to model complex real world conditions. Copies of his machine became the first computers at the Lawrence Livermore National Laboratory and Purdue University. On the blackboard is the Van der Pol equation, a non-linear second-order ordinary differential equation that can be used to model a nonlinear oscillator. For example his machine could mathematicaly model a generator on a triode for a vacuum tube with a cubic characteristic. The equation is also used to model chaotic behaviour when sinusoidal forcing is involved, represented by the the a·cos(ω·t) term.