@whynotsicence on Instagram: "🌀the geometry of the 13th century, the moment a circle produces a straight line The device in the video shows an ancient geometric principle called the ”Tusi Couple.“ It looks like two simple circles are spinning, but there’s an elaborate structure hidden in it where a straight line is born. When a small circle rotates at a constant rate within a large circle, the beads at the end of the small circle look like they are doing a ‘straight reciprocating motion’ back a