We have a Cenco and an Ealing Michelson student interferometer. These are used primarily to familiarize the students with this type of instrument. They learn how to adjust the instrument for monochromatic light and measure the wavelength of the green line of mercury. In addition they place a quarter wave plate in one leg of the interferometer and study the 1/2 fringe shift in the pattern when the plane of polarization is rotated by 90°, and the complete lack of pattern when the plane of polarization is at 45° to the optic axis of the quarter wave plate.