Analog Computing Component - Integrator (Four-Inch Disc)

Instruments for finding the area bounded by curved lines (integrators) date from the nineteenth century. This twentieth century example is based on a mechanism invented by British engineer James Thomson and used by his brother William (later Lord Kelvin) in constructing the first harmonic analyzer in 1876. As K.C. Epstein has recently shown, the American inventor Hannibal Ford improved the design, following ideas developed by Britons Pollen and Isherwood for the British Navy in the early twentieth century.

The integrator consists of a mechanism of hardened steel held in a metal frame. A disc at the bottom is linked by two adjacent balls to a rotating shaft at the top – there is a gear at the end of the shaft. Each of the balls has four vertical rollers on it. Rotating a horizontal gear at the front rolls the carriage for the balls crosswise.

A mark etched into the front edge of the base of the frame reads: U.S. NO. 772.

Ford's integrators were used by the U. S. Navy in devices for aiming guns on ships. They continued in use after Ford Instrument was acquired by Sperry in 1955. The precise date of this integrator is not known, although it most probably is from after 1930.

References:

A.B. Clymer, "The Mechanical Analog Computers of Hannibal Ford and William Newell," Annals of the History of Computing, 15, #2, 1993, 19-34.

K.C. Epstein, Analog Superpowers: How Twentieth-Century Technology Theft Built the National Security State, Chicago: University of Chicago Press, 2024.

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