Hartree, D. R., The Mechanical Integration of Differential Equations, The Mathematical Gazette, vol. 22, 1938, pp. 342-364.
Hartree, D. R., and A. Porter, The Construction of a Model Differential Analyser, Memoirs and Proceedings of the Manchester Literary and Philosophical Society, vol. 79, July 1935, pp. 51-72.
Other small scale differential analyzers built in England are covered in:
Beard, R. E., The Construction of a Small Scale Differential Analyser and Its Application to the Calculation of Actuarial Functions, Journal of the Institute of Actuaries, vol. 71, 1942, pp. 193-227.
Massey, H. S. W., J. Wylie, and R. A. Buckingham, A Small Scale Differential Analyser: Its Construction and Operation, Proceedings of the Royal Irish Academy, vol. 45, 1938, pp. 1-21.
A differential analyzer constructed in Germany is briefly described in the following:
Sauer, R., and H. Poesch, Integrating Machine for Solving Ordinary Differential Equations, Engineers Digest (American Edition), vol. 1, May 1944, pp. 326-328.
From the historical point of view there are some interesting papers on a machine for solving differential equations by Sir William Thomson (Lord Kelvin), including one by his brother James Thomson. They are in the Proceedings of the Royal Society, vol. 24, Feb. 1876, pp. 262-275. The method of integration by a machine is described, but the state of machine tools at the time was such that no accurate mechanism was constructed. Another interesting paper foreshadowing the differential analyzer is:
Wainwright, Lawrence L., A Ballistic Engine, Chicago: University of Chicago, thesis for Master’s Degree, 1923, 28 pp.
Some of the applications and mathematical limitations of differential analyzers are covered in: