A vacuum tube voltmeter is described, which, when adjusted by means of a glass electrode, becomes a static instrument. It gives values agreeing with the electrometer on all systems measured except on thick glass 3 electrode systems where the electrometer may be superior. The voltmeter has the advantage that high speed changes may be detected on feeding the output of the last tube into a recording oscillograph or simply using a fast moving indicating meter. The importance of elimination of minute polarization currents in accurate measurements of physical and biological systems of small electrochemical capacity is demonstrated.