The ancient Greeks noticed that a man with arms and legs extended described a circle, with his navel as the center.

The ancient Greeks noticed that a man with arms and legs extended described a circle, with his navel as the center.

古希腊人注意到一个四肢伸展的人画了一个圆圈，他的肚脐为中心。

-- Stephen Gardiner 斯蒂芬·加得纳