A free-fall technique has been used to measure the net vertical component of force on electrons in a vacuum enclosed by a copper tube. This force was shown to be less than $0.09mg$, where $m$ is the inertial mass of the electron and $g$ is 980 cm/${\sec }^2$. This supports the contention that gravity induces an electric field outside a metal surface, of magnitude and direction such that the gravitational force on electrons is cancelled.

• Received 2 October 1967

DOI:https://doi.org/10.1103/PhysRevLett.19.1049