A new method is described for the measurement of electron mobilities in gases. An electrical shutter method is employed in which the shutters take the form of two fine wire grids, alternate wires of which are connected to a high frequency alternating potential. Electrons pass through the grids only when the potential between adjacent grid wires is zero, and only electrons which cross the gas space in one half-cycle are received at the collecting electrode. A sharp maximum is thus observed in the electrometer current when the drift velocity of the electron multiplied by the time of one half-cycle is equal to the distance between the grids. The theoretical shape of the current curve is compared with experiment and good agreement observed. Measurements have been made between $\frac{X}{p}$ of 0.03 and 20, and the values obtained are compared with the Compton mobility equation.

• Received 22 November 1935

DOI:https://doi.org/10.1103/PhysRev.49.388