Fermat's principle is not so much a computational device as it is a concise way of thinking about the propagation of light. 费马原理更多的是对光的传播的一种简明看法，而不是一种计算工具。
The paper is to prove the refraction on two kinds of medium interfaces of electric displacement line using the boundary condition of the electric field and Fermat Principle. 利用电场边界条件和费马原理证明电位移线在两种介质界面上的折射。
