文章首先提出一种游泳池中泳者“身首分离”的折射现象，然后介绍了水下物点经水面折射成像的严格位置作为铺垫，利用平面几何与三角函数知识，推导出水下物点的像与物( 即泳者“身首”) 在观察者眼中的视觉分离距离函数，代入数据验证了实际观察.文章利用所推得的几个函数辅以作图，分析出水下像与物的视觉分离距离将随视角及观察者距离的增大而增大，但却随物点深度的增加先增加后减小直至趋于零.文章又对几个特殊的情形进行了讨论，同时指出本文中视觉分离距离的解析结果与数值求法各有其优势和局限性.

This paper first proposes a refraction phenomenon of the swimmer's “body head

separation”in the swimming pool; and then，as the bedding，it introduces the strict image position

of the underwater object refracting through the water surface. Using the knowledge of plane

geometry and trigonometric function，the visual separation distance function of the underwater

object's image and object ( that is，the swimmer's “body head”) in the eyes of the observer are

derived，and the actual observation is verified by the data. By using the functions

deduced and graphs drawed，the paper finds that the visual separation distance between the

underwater image and the object will increase with the increase of the visual angle and the

distance of the observer，but it will first increase and then de- crease until it tends to zero with

the increase of the depth of the object point. Several special cases are discussed， and it is

pointed out that the analytical results and the numerical method of the visual separation distance

have their own advantages and disadvantages.