The expression of the optical path is educed when the spectroscope in Michelson interferometer is reversed. The reason of the appearance of elliptic or hyperbolic interference fringes is explained.

• 推导了迈克耳孙干涉仪分光镜放反的情况下光程的表达式；解释了出现椭圆干涉条纹或双曲线条纹的原因.