translation.en: It has curves in two directions, one curve upward and opposite transverse curve down the other, so any kind of perturbation spreads the forces over the surface of this type of shape.
translation.zh: 它在两个方向上都有弧线。 一条曲线向上，并且相反的横向曲线向下。 因此可经受任意一种变化 越过这种形状的表面