It is thus futile to compare the absolute voltages met with at two stations, unless allowance can be made for the influence of the environment.
With a view to this, it has become increasingly common of late years to publish not the voltages actually observed, but values deduced from them for the potential gradient in the open in volts per metre.
At Such Times Gradients Of 400 Or 500 Volts Per Metre Are By No Means Unusual At Kew, And Voltages Of 700 Or Boo Are Occasionally Met With.
A, B, C, D, E, F, Terminals to which standard cell or voltages to be tested are attached.
Ayrton and others, for measuring voltages from 10,000 volts down to 1 volt.
Electrostatic voltmeters are now almost entirely used for the measurement of high voltages from 2000 to 50,000 volts employed in electrotechnics.
Like the corresponding ammeters, they have the great advantage that the scales are equidivisional and that there is no dead part in the scale, whereas both the electrostatic and electrothermal voltmeters, above described, labour under the disadvantage that the scale divisions are not equal but increase with rise of voltages, hence there is generally a portion of the scale near the zero point where the divisions are so close as to be useless for reading purposes and are therefore omitted.
For the measurement of voltages in continuous current generating stations, movable coil voltmeters are much employed, generally constructed then in the "edgewise" pattern (fig.
Another muchused method of measuring con tinuous current voltages or unidirectional potential difference employs the principle of potentiometer.