Thanks to Ben for sending this my way. Here’s what Karl Sims (the guy who built this bad boy) has to say about it:
“A harmonograph is a mechanical device that uses swinging pendulums to draw pictures, believed to be originally invented in 1844 by Scottish mathematician Hugh Blackburn. There are other types of harmonographs, but this 3-pendulum rotary type gives a wide variety of pleasant results, and is fairly easy to build once you’ve settled on a design and have acquired the appropriate materials and tools. This is a great project to do with kids and can result in endless experiments creating new types of geometric designs.”
If you want to make your own, check out Karl Sims’s site for instructions.