Abstract: An interference phenomenon in the experiment of adjusting spectrometer is discussed mainly. When turning the glass used in the experiment to adjust the verticality between the axis of telescope and the axis of the apparatus, an interference phenomenon together with variation in width of the stripe can be seen. The reason of the phenomenon and variation of the stripe in theory are analyzed. If one knows how thick the reflector is and the wavelength of the light used in the lab in advance, one can use this phenomenon to measure the refractive index of the glass. The calculating method, data processing and error analyzing are also shown.

Key words: spectrometer, interference stripe, thickness and density changes of the stripe, refractive index