Abstract: An apparatus for sensing the electrical potential of a positive electrostatic field which is primarily below the surface of the earth, and observing the changes in a series of each reading is accomplished by means of an instrument employing a column of mercury in a small-diametered quartz tube, which is open on its lower end with means connecting to the other end for changing the level of mercury within the tube. A conductive coating on the exterior of the tube is connected to an electrometer and the coating is arranged to be selectively grounded or ungrounded in conjunction with changing the level of the mercury column. The readings for the electrometer provide a measure of the electrostatic field.

Abstract: A novel method for detecting charge on large bodies such as the earth is accomplished by means of disclosed apparatus which includes a vertical column of mercury having an associated electrode which is capacitively coupled to the mercury column when the mercury level is above the position of the electrode. By establishing an initial unipotential state for the apparatus by short circuit connection of the electrode and mercury column to the earth and an electrometer connected between the electrode and the earth which is initially short-circuited across its terminals the apparatus is conditioned to sense the charge of the large body to which it is connected (the earth) by moving the mercury column up and down past the position of the electrode with the electrometer open-circuited and thus connected between the electrode and earth during the passage of the mercury in one direction past the electrode.