The phrase "early computer" usually evokes a room full of whirring, cabinet-sized machines or punch cards. Nothing wet there. But at least a couple of early innovators built computers that ran on water.
Russian scientist Vladimir Lukyanov solved partial differential equations in 1936 using a machine that used "a series of interconnected, water-filled glass tubes," writes Jamie Condliffe for Gizmodo. "The levels in certain tubes gave the answers, while adjusting taps and plugs changed variables." In a similar way, water flow in a 1949 computer modeled economic processes, Klint Finley reports at Wired. The MONIAC (which stands for Monetary National Income Analogue Computer) was created by Bill Philips, then a student at the London School of Economics.
The six-and-a-half-foot tall computer was innovative not for the calculations it could do but for the way it displayed the results. For Inc., Doron Swade writes:
The problem was not computer processing power but visual display. Phillips wanted to demonstrate economic behavior, to show students immediately and clearly how the elements of a national economy interact. Because the early computers had no visual-display units -- no monitors, no screens -- the behavior of the mathematical model remained hidden. Phillips's choice of hydraulics and transparent plastic was deliberate, and his reasoning sound.
The series of tubes and tanks are analogues for part of the economy. Water flowing through the pipes represents money flow. Steven Strogaz writes in the New York Times,:
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.
Cambridge University has one of only two working versions of the machine, demonstrated in this video:
The MONIAC was originally conceived as a teaching aid, Swade writes for Inc., but it was intriguing enough that Ford Motor Company and the Central Bank of Guatemala also bought versions of the machine. The only other working copy is on display at the Reserve Bank of New Zealand Museum. Phillips, after all, was a New Zealand economist.