Liquidity: Irving Fisher's Hydraulic Computer

Back in 2011 we looked at William Phillips (he of the curve) and his hydraulic model:

"The computer model that once explained the British economy (and the new one that explains the world)".

Here's an explanation of the Phillips machinevia Conversable Economist:

...In the New Zealand central bank publication, Tim Ng and Matthew Wright describe the functioning of MONIAC this way: "Separate water tanks represent households, business, government, exporting and importing sectors of the economy. Coloured water pumped around the system measures income, spending and GDP. The system is programmable and capable of solving nine simultaneous equations in response to any change of the parameters, to reach a new equilibrium. A plotter can record changes in the trade balance, GDP and interest rates on paper. Simulation experiments with fiscal policy, monetary policy and exchange rates can be carried out. Although the MONIAC was conceived as a teaching tool, it is also capable of generating economic forecasts....

The post continues on to Fisher:

...Fisher’s thesis went beyond these writings in one striking respect: influenced by Gibbs’s work in mechanics, Fisher not only imagined but actually built a hydraulic mechanism to simulate the determination of equilibrium prices and quantities—in effect, a hydraulic computer in the days before electronic computers ..."

Oddly enough, Fisher also wrote a paper that is an early harbinger of the Phillips curve literature. As Dimand and Betancourt write: "In a series of articles, Fisher correlated distributed lags of price level changes with economic activity and unemployment. His article “A Statistical Relationship between Unemployment and Price Level Changes” (1926 [1973]), little noticed when first published by the International Labour Office, attracted rather more attention when reprinted almost 50 years later in the Journal of Political Economy as “Lost and Found: I Discovered the Phillips Curve—Irving Fisher.”

I'm not aware of any working models of Fisher's hydraulic computer, nor of any photographs of a working model. But  back in 2000, William C. Brainard and Herbert E. Scarf took on the task of investigating how the model worked in "How to Compute Equilibrium Prices in 1891."  They reprint these sketches of Fisher's hydraulic computer from his dissertation. It apparently consisted of a series of cisterns, rods, floats, bellows, and tubes. It represents three consumers and three goods that they consume.

Apparently, Fisher used his hydraulic model of the economy as a teaching tool for 25 years. Brainerd and Scarf write (references omitted):

"Fisher regarded his model as "the physical analog of the ideal economic market," with the virtue that "The elements which contribute to the determination of prices are represented each with its appropriate role and open to the scrutiny of the eye ..." providing a "clear and analytical picture of the interdependence  of the  many elements in the causation of prices ... " Fisher also saw the machine as a way of demonstrating comparative static results, "... to employ the mechanism as an instrument of investigation and by it, study some complicated variations which could scarcely be successfully followed without its aid. ... MORE