楕圓 (翻譯)

Mark out two points H and I, and run a loop of string around them. Then keep moving the point E while keeping the string taut. The curve traced out by E will then be an ellipse.

釘上兩個釘子 H 與 I, 用細繩圈套住兩個釘子. 一支鉛筆 E 圈套在繩套裡, 繃緊了邊滑邊畫, 楕圓便出來了.