ClipArt ETC
"An instrument for observing or detecting the existence of free electricity, and, in general, for determining its kind. ... The simplest electroscope consists of pith-balls suspended by silk threads." -Whitney, 1911

Pith-Ball Electroscope

"An instrument for observing or detecting the existence of free electricity, and, in general, for determining…

"An instrument for observing or detecting the existence of free electricity, and, in general, for determining its kind. ... Quadrant electroscope, a form of pith-ball electroscope which serves to measure roughly the degree of electrification by the rise of the pith-ball as indicated by the motion of the rod carrying it on a graduated semicircle." -Whitney, 1911

Quadrant Electroscope

"An instrument for observing or detecting the existence of free electricity, and, in general, for determining…