双曲狭缝    

        在空间中一条直线运动轨迹形成的曲面成为直纹面。这条直线叫母线。    这里所展示的直纹面是单叶双曲面，当把该直纹面从中心侧剖，就会看到与双曲狭缝板相同的平面。而两条狭缝正是平面上的截线。直杆是生成这个直纹面的母线 ，所以它可以顺利通过平板上的双曲狭缝。

HYPERBOLOIDSLIT    

        The curved surface formed by the movement track of a straight line in space is called a ruled surface, and the line is called the generating line.    The ruled surface exhibited here is a univalent hyperboloid. Cut the ruled surface from side of the center, and you will see the same surface with the hyperboloid slit board, and the two slits are the transversals on the plane. The straight pole is the generating line producing the ruled surface. That’s why it can smoothly pass through the hyperboloid slit on the plane board.