Afflux-voltmeter for magnetic tests

R. L. Sanford: For the determination of the average value of an alternating electromotive force a rectifier of some kind is necessary. While somewhat difficult to keep in good working condition, the rectifying commutator, either mounted directly on the generator shaft or driven by a synchronous motor, has been, up to the present time, the only satisfactory apparatus for the purpose. The commutator has a number of disadvantages which are obvious to any one that has had occasion to use it and the development of a really satisfactory method for measuring average volts represents a distinct advance in the art.