Behold the pendulograph (now commonly called harmonograph)! These incredible images were made with a drawing machine attached to pendulums tuned to musical frequencies too low for the human ear (but musical frequencies all the same). While these pendulographs were made in 1880 and 1881, the machine works roughly the same way as this one and this one, as far as I can tell.
Have you long considered your favorite chord or interval? Flip through these babies and find their visual representation.
I highly recommend that you check out the rest of these images in our digital library, and read the flowery prose of Reverend John Andrew; his published explanatory work on the pendulograph is here, and his unpublished album of pendulograph works is here.
The Pendulograph and Album, Reverend John Andrew, 1881, Historical Society of Pennsylvania Am. 83693 volumes 1 and 2.