This is a mathematical transformation where we create a sphere, and a set of points on this sphere correspond to vortex lines and their evolution over time.

我们在这个数学变换中创造一个球体，球体上的一系列点与涡流线及其演变相符。

And, when you think about it, any rigid object rotating around a fixed axis is basically a set of points, all moving along circular paths.

而且，仔细想想，任何围绕固定轴旋转的刚性物体基本上都是一组点，它们都沿着圆形路径移动。