When I read Making Money by Terry Pratchett I was intrigued by the financial computer he described. Constructed from various tubes, taps and joints, it used coloured water to model the Ankh-Morpork economy, allowing the resident financial genius to make startlingly accurate predictions about the ramifications of small changes. I don’t know if the idea popped unbidden into the fertile imagination of Sir Terry but, reading Farmer Buckley’s Exploding Trousers (which sounds like it could be Pratchett but is, in fact, a popular science book from New Scientist) it turns out that not only had the idea been thought of before but also that it had been built and found to work very well.

According to the chapter “Liquid Assets” (pp160-163), the same concept was dreamed up, built and unveiled as a working concept by Bill Phillips in 1949. Nowadays such work is done by flowing electrons in computers rather than flowing water but it struck me as fascinating. Of course, the original invention can’t have been perfect since even with hugely powerful computers and refined software available to economists across the world, they clearly don’t understand how everything works well enough to fix it!