Harmonographs are mechanical devices that employ coupled pendula (aka: “pendulums”) to control the movement of a pen relative to a drawing surface (e.g., a sheet of paper). The pen’s motion can produce some strikingly beautiful curves.
I had never heard of harmonographs until I read Mike Croucher’s post: Simulating Harmonographs. Instead of building a physical apparatus, Mike simulated harmonographs with Mathematica. The resulting drawings are indeed most aesthetically pleasing:
[ image courtesy of Mike Croucher ]
Drawings produced with harmonographs remind me of the drawings I used to make with the Spirograph toy when I was a kid. They also remind me of the Lissajous curves I liked to visualize on the oscilloscope when I was an undergraduate student and spent countless hours in the electronics laboratory.