本文利用惠更斯原理推得了光线自各向同性介质入射到单轴晶体边界面上时所产生的 e 光光线的折射关系式，并给出了相关各角度的符号规则.该关系式适用于光轴位于入射面内的各种情形. 运用此关系式，本文讨论了几种特殊情况，结果发现，与 o 光类似，若入射光线在入射面内绕入射点转动，那么 e 光也会发生相同方向的转动; 在特定条件下，e 光可以和入射光处于法线的同侧; 当光线垂直界面入射时，e 光光线存在最大折射角.

The refraction relation of the extraordinary light ray with the incident light on

uniaxial crystals from isotropic media is derived by using Huyghens principle. And the matched

sign convention is also given. The refrac- tion relation is appropriate for the situations where

the optical axis is in the incidence plane. Three special cases are discussed with the refraction

relation. The results are as follows: when the incident light ray rotates around the inci- dence

point in the incident plane，the extraordinary light ray must rotate in the same direction; under

the particular conditions，the extraordinary light ray can appear at the side of the

interfacial normal where the incident light ray exists; the refraction angle of the

extraordinary light ray has a maximum value when the incident angle is 90°.