Harmonographs are mechanical devices that draw pictures by swinging pendulums, believed to be invented in 1844 by Scottish mathematician Hugh Blackburn. In my 3-pendulum rotary harmonograph, two lateral pendulums swing back and forth at right angles to each other (one side to side, another front to back) with arms connecting to a pen. A third “rotary” pendulum moves the paper by swinging on any axis or in circular motions.
This harmonograph gives a wide variety of pleasant results, and is fairly easy to build. It’s a great project to do with kids and can result in endless experiments creating new types of geometric designs. Here’s how you can create your own.