The Differential Analyzer as an Active Mathematical Instrument: Control Applied to Mechanism and Circuitry

As part of a 1989 ACC Plenary Lecture, we feature here the essential role played by amplification and control in the successful development of the differential analyzer (DA). This first occurred with the introduction of the capstan torque amplifier in Vannevar Bush's largely mechanical form (as the 1930 MDA) and then later with use of the voltage operational amplifier in an electronic embodiment (as the 1947 EDA or electronic analog computer). Certain essential components and features of both MDAs and EDAs are outlined and contrasted, where the fast all-electronic EDA best exemplifies the distinctive benefits attending the evolution from mostly mechanical to fully electrical implementation.