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July 11, 2008

MONIAC: adventures in analogue computing

Thanks to the wily Kirk Jackson and the, er, New Zealand Association of Economists, I had the pleasure this afternoon of seeing an unusual piece of computing history in action.  MONIAC, the Monetary National Income Analogue Computer, also known as the Phillips Machine, was an analogue computer invented by Bill Phillips (he of curve fame) to model and simulate the relationships between various economic factors.  Nothing unusual about that, except that it was invented in the 1940s... and instead of processing 0s and 1s, it processed water.  The Reserve Bank of New Zealand has one of the few Phillips Machines still around and in working order, and as part of a lunchtime session for the NZAE conference they had cranked it up and were demonstrating it.

The machine works by circulating water around a network of tanks, taps, pumps and pipes.  Values are represented by the levels of water in various tanks, parameters by opening and closing taps or moving valves up and down, and the key readouts of income and interest rates are recorded by pens moving against graph paper.  Water, of course, represents money, though demonstrator Geoff Bertram was careful to refer to it at all times as "the circulating medium."  I have to be a bit vague about what sort of things the various tanks and taps and throttles represented: explanations of the various bits in terms of private sector liquidity requirements and endogenous money supply undoubtedly made sense to the mainly economist audience but I'm afraid I struggled. Still, I gathered it was a pretty accurate simulation of the economic theories of the 1940s and 1950s; according to the demonstrator it effectively shut down a major debate of the time by convincing both sides that their arguments were actually compatible.

Of course, not being programmable, MONIAC can't be updated to reflect new factors and new economic conditions (such as globalisation).  The demonstrator did, however, relate how one lecturer used to set up two MONIACs, one representing the US economy and one representing the UK, hook up the relevant bits of piping between the two machines, and challenge two sets of students to do the best for "their" economy, so within the constraints of the model there was a certain amount of flexibility.

On the other hand, MONIAC's analogue approach still rivals the digital approach in some ways.  "It's solving nine simultaneous differential equations," noted the demonstrator.  Given the sophistication of modern numerical techniques, and the effort that has undoubtedly been poured into economic simulation and prediction, it's no surprise that the Phillips Machine has been superseded, but I suspect that ultimately the digital equivalents are just badly simulating water flow, only more flexibly and a lot faster.  One member of the audience, noting that the Phillips Machines had been used largely for educational purposes, asked Dr Bertram how he would present the same ideas now.  "I'd draw a hydraulic diagram," he replied.

This being a computer demo, of course, things did not go quite to plan; but this being an analogue computer demo, they went not to plan not through the usual syntax errors and unhandled exceptions, but instead because the bit of plastic representing the level of imports had fallen off and had to be stuck back on with blu-tack, and the export doohickey had become stuck against its housing.  Kernel fans will also be pleased to know that the Phillips Machine's ultimate failure mode is also described as "dumping," except in this case you end up with wet shoes and a massive carpet cleaning bill instead of just a nice convenient file.  "Now it sits in this bath here, and we've fitted a drain through to the outside," noted Dr Bertram ruefully.

(Incidentally, Bill Phillips was a New Zealander: connoisseurs of Kiwiana will therefore note that the use of blu-tack to hold the level of imports steady counts as Kiwi ingenuity, while the failure mode of spewing the "circulating medium," i.e. the national economy, all over the floor represents classic Kiwi ingenuity, or possibly Rogernomics.)

This highlights another interesting feature of the analogue approach: its unpredictability.  When the demonstrator was showing us "fiscal shocks" and "monetary shocks," he commented on how long the simulated economy took to react to stimuli such as suddenly injecting government investment or restricting lending.  "Sometimes they take 30 seconds, sometimes they take five minutes," depending on the mood of the machine.  Given the unpredictability of real economies, this in some ways seems like an attraction of the analogue approach. The downside? "Sometimes you'll be standing there talking about how things eventually come back to equilibrium, and everything's crashing and burning behind you."  At least when my demos tank they don't take national economies with them.

Due to short notice, I don't have any pictures, but Wikipedia does (as does NZIER at the link above), and if you're in Australia or the UK, I gather there are also kinda-maybe-working machines at Melbourne University and at the Science Museum.  There is also apparently one lost in Guatemalan jungle, so any budding Indiana Joneses of computing, now's your chance.

July 11, 2008 in Science, Software, Usability | Permalink


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Wily? Pity I couldn't make it along, it sounds intriguing. :)


Posted by: Kirk Jackson at Jul 11, 2008 9:57:33 PM

MONIAC has got a chapter in Electronic Brains which says the Science Museum one doesn't work (which seems to be implied by the SM website saying 'It ran until May 1992'). I got the impression the tubes may be filled with something solid that looks like coloured liquid to give an impression of what it looks like.
Haven't been to the Science Museum in a while, I assume it is still a national disgrace.

Posted by: Harvey Pengwyn at Jul 11, 2008 9:58:02 PM