The early history of control theory is explored, beginning with the contributions of Hooke and Huygens in the seventeenth century, and ending with Airy’s papers of 1840 and 1851. It is argued that, despite appearances to the contrary, Huygens’ speed control system is actually a feedback system. A proof is given that the Huygens-Hooke parabolic governor has integral action, thus eliminating offset. A detailed exposition of Airy’s techniques is given. It is shown that he used a disguised form of linearization. Airy’s system is also investigated using block diagram and Nyquist diagram techniques. The centrifugal governor is shown to have a tendency to resonance which adversely affects closed-loop stability; in agreement with Airy’s findings. Biographical notes on the main contributors are included in order to bring out the background and motivations of their theories.

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