Here’s a 2009 New York Times column about a hydraulic model of the economy.
In the front right corner, in a structure that resembles a large cupboard with a transparent front, stands a Rube Goldberg collection of tubes, tanks, valves, pumps and sluices. You could think of it as a hydraulic computer. Water flows through a series of clear pipes, mimicking the way that money flows through the economy. It lets you see (literally) what would happen if you lower tax rates or increase the money supply or whatever; just open a valve here or pull a lever there and the machine sloshes away, showing in real time how the water levels rise and fall in various tanks representing the growth in personal savings, tax revenue, and so on. This device was state of the art in the 1950s, but it looks hilarious now, with all its plumbing and noisy pumps.
When it debuted back in November 1949, the leading thinkers at the London School of Economics crammed into the seminar room, some having come just to laugh, others gaping in amazement at the thing in the middle of the room, which had been cobbled together in a garage, with a pump cannibalized from an old Lancaster bomber.
Maybe it shouldn’t be quite so surprising. Before there were digital computers, there were “analog computers”, essentially circuits that could simulate various types of systems at equilibrium. Different types of systems have analogous building blocks and processes, like storages, flows, and resistances. As Howard T. Odum showed us, you can use these basic building blocks to model all types of systems, from physical to biological to socioeconomic.