The effect of stress on contact potential has been measured semiquantitatively in Al, Cu, Au, steel, and brass using a high-sensitivity version of the Kelvin method. The observed shifts are in all samples positive (i.e., the electric field outside the sample is more positive when pressure is applied) and the magnitude is a few microvolts per kg/${\mathrm{cm}}^2$ applied stress. Both sign and magnitude agree with the theories of Dessler, Michel, Rorschach, and Trammell, and of Herring, provided one assumes that gravitationally produced stress is equivalent to hydraulically produced stress.

• Received 15 January 1969

DOI:https://doi.org/10.1103/PhysRevLett.22.700