Varley, who proposed to make use of it in a telegraphic receiving instrument.4 In Dolbear's instrument one plate of a condenser was a flexible diaphragm, connected with the telephone line in such a way that the varying electric potential produced by the action of the transmitting telephone caused an increased or diminished charge in the condenser.
An exactly similar expression holds good in hydrokinetics, provided that for the electric potential we substitute velocity potential, and for the electric force the velocity of the liquid.
VOLTMETER, an instrument for measuring difference of electric potential (see Electrostatics) in terms of the unit called a volt.
ELECTROSCOPE, an instrument for detecting differences of electric potential and hence electrification.
He has constructed a capillary electrometer by which differences of electric potential less than o oi of that of a Daniell's cell can be detected by the difference of the pressure required to force the mercury to a given point of a fine capillary tube.