在利用迈克耳孙干涉仪观察白光干涉并测量透明介质折射率的实验中，一个关键的步骤是在没有引入待测介质时观察到白光干涉的基础上，移动一臂的反射镜（动镜）使得引入介质后干涉条纹再次出现．在实际的实验中，会出现动镜移动的距离为标准结果一半时就观察到干涉图样的情况．本文从理论上分析这一现象出现的原因，并设计对比实验进行了实验分析．本文的理论和实验结果表明这种现象源于光束单次通过尺寸较小且只占视场小部分区域的待测介质．另外，该次干涉条纹出现在介质区域之外，而标准结果的条纹出现在介质区域之内．

In the experiment of observing white light interference with a Michelson interferometer to measure refractive index of a transparent medium, a key step is to move a the moving mirror of the interferometeron the basis of observing white light interference without the introduction of the medium to be measured,so that the interference fringes appear again after the introduction of the medium. In actual experiments, interference patterns can be observed just when the moving mirror moves halfstandard distance.In this paper, the reasons for this phenomenon are theoretically analyzed, and comparative experiments are designed for experimental analysis. The theoretical and experimental results show that this phenomenon originates from the single passage of the beam through the medium which is small in size and occupies only a small part of viewfield.In addition, the interference fringes for this case appear outside the medium region, while the interference fringes for the standard case appear inside the medium region.