Lissajous

I found an old photo of a physics experiment I did in highschool back in 1979.
It shows a Lissajous curve. A lightbulb on a string draws the lines of the curve on
a film in an analogue camera set to high exposure time.
Black/white only since I developped the picture in the old-fashioned way (with patterson development tank and fluids; no smartphones with Megpixels available at that time).