The differential analyzer as an active mathematical instrument

The essential role played by amplification and control in the successful development of the differential analyzer is described. This first occurred in 1930 with the introduction of the capstan torque amplifier in Vannevar Bush´s largely mechanical form, and then in 1947 with the use of the voltage operational amplifier in an electronic embodiment that was called an electronic analog computer. Certain essential components and features of both machines are outlined and contrasted, highlighting how the fast all-electronic machine best exemplifies the distinctive benefits attending the evolution from mostly mechanical to fully electronic implementation.<>