 Fig . 8 illustrates the operation of a Fourier transform spectrometer , which is essentially a Michelson interferometer with one mirror movable . ( A practical Fourier transform spectrometer would substitute corner cube reflectors for the flat mirrors of the conventional Michelson interferometer , but for simplicity , the illustration does not show this . ) An interferogram is generated by making measurements of the signal at many discrete positions of the moving mirror . A Fourier transform converts the interferogram into an actual spectrum . 
