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The Rein "Thermostromuhr", the best method available for measuring flow in unopened vessels, is limited to mean flow measurements. In this laboratory a new method was developed which can follow rapid flow changes and which, besides, possesses the further advantage that the deflection bears a linear relation to the flow.This flowmeter is based on the principle that an electromotive force is induced in a conductor moving so as to cut the lines of force in a magnetic field. If a wire is moving through the field in a direction perpendicular to its own axis and to the lines of force, then the potential difference at the ends of the wire is given by the expression :where E denotes the induced voltage, H is the strength of the magnetic field, 1, the length of the wire and v, its velocity.A steady potential difference can be obtained by moving an endless metal belt, mercury or an electrolytic solution between the magnet poles. Here 1 would indicate the width of the conductor used. The induced electromotive force generated in the case of the solution can be tapped by introducing 2 non-polarizable electrodes through the wall of the tube through which the liquid is flowing. Since the induced voltage is proportional to the velocity of fluid flow, the current flowing through the galvanometer connected to these electrodes will be a linear function of the rate of flow. This was verified by actual trial with solutions of various concentrations of copper sulphate and sodium chloride using copper electrodes for the former and silver-silver chloride electrodes for the latter.
Alexander Kolin (Thu,) studied this question.