In the 1980s people in chemistry labs that needed to find the area beneath a curve used to print/plot the curve, cut out the area and weigh it. This worked quite well as they had accurate scales.
In a related vein, Ars Technica writer Sean Gallagher did a fantastic story on the US Navy's analog fire guidance computers a few years ago:<p><a href="https://arstechnica.com/information-technology/2014/03/gears-of-war-when-mechanical-analog-computers-ruled-the-waves/" rel="nofollow">https://arstechnica.com/information-technology/2014/03/gears...</a><p>The instruction videos alone are worth the visit. Geekery of the first order.
I know of two excellent examples of this. One is an entertaining modern attempt to recreate economic models with a fluid computer: <a href="https://vimeo.com/131690448" rel="nofollow">https://vimeo.com/131690448</a><p>The other is the fucking fantastic Bay Model, a 1:1000 physical model of the San Francisco Bay: <a href="https://en.wikipedia.org/wiki/U.S._Army_Corps_of_Engineers_Bay_Model" rel="nofollow">https://en.wikipedia.org/wiki/U.S._Army_Corps_of_Engineers_B...</a><p>It was built in the 1950s to study the effects of various plans, including one proposal to divert all incoming rivers to "productive" use. It was eventually made obsolete by computer simulation, but it's still there. I bring a lot of my nerdy out-of-town visitors there; it's amazing to walk around on a 2-acre simulation.
There's a little more info in this (somewhat wonderful) article: <a href="https://pruned.blogspot.com/2012/01/gardens-as-crypto-water-computers.html" rel="nofollow">https://pruned.blogspot.com/2012/01/gardens-as-crypto-water-...</a>
> he water level in various chambers (with precision to fractions of a millimeter) represented stored numbers<p>I wonder how did they deal with thermal expansion. Maybe instead of using water at room temp they heated it to something higher and then a thermostat took care of it? But it still would be very hard to distribute heat evenly.
If you squinted, you might consider the U.S. Army Corps of Engineers Bay Model a giant low tech special purpose water computer.<p><a href="https://en.wikipedia.org/wiki/U.S._Army_Corps_of_Engineers_Bay_Model" rel="nofollow">https://en.wikipedia.org/wiki/U.S._Army_Corps_of_Engineers_B...</a><p>>The U.S. Army Corps of Engineers Bay Model is a working hydraulic scale model of the San Francisco Bay and Sacramento-San Joaquin River Delta System. While the Bay Model is still operational, it is no longer used for scientific research but is instead open to the public alongside educational exhibits about Bay hydrology. The model is located in the Bay Model Visitor Center at 2100 Bridgeway Blvd. in Sausalito, California.
I believe now one could use microfluidics to leverage similar principles but miniaturize it almost into the size of a chip.<p>Here is an interesting demo:<p><a href="https://youtu.be/7z8I7awRYY4?t=114" rel="nofollow">https://youtu.be/7z8I7awRYY4?t=114</a>
Reminds me of the stone/water brains of the Quatzoli people in Ken Liu’s short story, "The Bookmaking Habits of Select Species".<p><a href="http://www.lightspeedmagazine.com/fiction/the-bookmaking-habits-of-select-species/" rel="nofollow">http://www.lightspeedmagazine.com/fiction/the-bookmaking-hab...</a>
I'm not sure how different this is to the ball integrator?[0] or Vannevar Bush's differential analyser?[1] The water computer article says partial differentiator, then integrator, it's unclear.<p>[0] <a href="https://en.wikipedia.org/wiki/Ball-and-disk_integrator" rel="nofollow">https://en.wikipedia.org/wiki/Ball-and-disk_integrator</a><p>[1] <a href="https://en.wikipedia.org/wiki/Differential_analyser" rel="nofollow">https://en.wikipedia.org/wiki/Differential_analyser</a>
This reminds me of "rod logic" computers: <a href="https://hackaday.com/2015/10/19/rod-logic-and-graphene-elusive-molecule-scale-computers/" rel="nofollow">https://hackaday.com/2015/10/19/rod-logic-and-graphene-elusi...</a>
Similarly there was a story about a ~computer based on water surface tension to encode complex equations and let the physics approximate a solution in parallel. Can't find the name though.
If I recall correctly, the world3 model which the authors of 'the limits to growth' used also utilized fluids to simulate the increasing, or diminishing influence of different factors on our ecosystem.
More details<p><a href="https://pruned.blogspot.com/2012/01/gardens-as-crypto-water-computers.html?m=1" rel="nofollow">https://pruned.blogspot.com/2012/01/gardens-as-crypto-water-...</a>