further reading

Priestley, J., & Henly, W. (1772). An account of a new electrometer, contrived by Mr. William Henly, and of several electrical experiments, made by him, in a letter from Dr. Priestley, F. R. S. to Dr. Franklin, F. R. S. In: Philosophical Transactions of the Royal Society of London, 62, 359-364.

Henley's Quadrant Electrometer

branch of study: electricity / electrostatics
inventor: William Henley, 1770

Henley's variation of a quadrant electrometer consists of an upright column with a brass stand. Attached to the column is a wire with an elder pith ball. If the instrument is charged, the ball will be repelled from the brass stand due to electrostatic forces. The magnitude of pepulsion can be read from a hemisphric scale.
The instrument was developed by William Henley and supposedly the first of its kind.