An amplifying lever system used for measuring piezoelectric deformations of quartz and tourmaline plates is described. Interference fringes are formed between a semi‐transparent coating of silver on glass and a mirror on the long end of a lever. With an arm ratio of 1864 to 1 the sensitivity of the lever is such that a displacement of a knife edge on the short end of about 0.15A can be detected. The chief difficulty in its use was found to be disturbance from vibrations. Sources of error, possible improvements, and possibilities for other uses are discussed.