Harmonograph

A harmonograph is a mechanical apparatus that employs pendulums to create a geometric image.

The devices, which began to appear in the mid-19th century and peaked in popularity in the 1890s, cannot be conclusively attributed to a single person, although Hugh Blackburn, a professor of mathematics at the University of Glasgow, is commonly believed to be the official inventor.

[1] A simple, so-called "lateral" harmonograph uses two pendulums to control the movement of a pen relative to a drawing surface.

A particular type of harmonograph, a pintograph, is based on the relative motion of two rotating disks, as illustrated in the links below.

In the 1870s, the term harmonograph is attested in connection with A. E. Donkin and devices built by Samuel Charles Tisley.

This was first discussed by James Dean in 1815 and analyzed mathematically by Nathaniel Bowditch in the same year.

The bob consequently follows a path resembling a Lissajous curve; it belongs to the family of mechanical devices known as harmonographs.