| "The electrical charge is roughly measured by the quadrant
or Henley's electrometer, which is attached to the conductor. This
is a small electric pendulum, consisting of a wooden rod to which is attached
an ivory or cardboard scale. In the centre of this is a small whalebone
index, movable on an axis, and terminating in a pith ball. Being attached
to the conductor, the index diverges as the machine is charged, ceasing
to rise when the limit is attained."
From Ganot, Physics (William Wood and Co., New York, 1883) pg 677.
These four examples are in the Garland Collection of Classic Physics Apparatus at Vanderbilt University, and are unmarked.
At the far right is an electrometer with the name of B. Pike and Son of New York on it. However, it looks very much like the Harris electrometer at the left; the foot, not shown in the diagram, has the same "brass ferule and pin" for inserting into conductors to indicate their potential. The 1856 catalogue of Benjamin Pike of New York lists this at $1.75 and $2.00 with the ivory scale.
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