The apparatus for measuring contact potential differences between solid‐solid or solid‐liquid by the vibrating plate method of Zisman has been simplified in two ways. The plate is driven by a radio loudspeaker powered by the ordinary 60‐cycle current and the null point is determined with an oscillograph instead of earphones. Spurious effects arising when leaves are measured are avoided by use of nonpolarizing connections through a calomel half‐cell, and other stray potentials are eliminated by very careful shielding.