A voltmeter based on the lines of the quadrant electrometer. It includes
two sets of quadrants, each oppositely excited by one of the two parts,
whose potential difference is to be determined. They attract each other
against a controlling force as of gravity.

One form has the two sets poised on horizontal axes, bringing the parts
so that the flat quadrants move in vertical planes.

In another form a number of quadrants are used in each set, the members
of the two sets alternating with each other. One set is fixed, the
others move and carry the index.