ClipArt ETC
"Cavallo's electroscope embodies the double pendulum principle. It consists of two fine silver wires loaded with small pieces of cork or pith, and suspended inside a small glass cylinder. Through the cap which closes the cylinder passes the stout wire from which the pendulums are suspended. This wire ends in a thimble-shaped dome A, which comes down very nearly to the cap; the outside of the cap is part of the wire and covered with sealing wax, and the object of the dome is to keep moisture from the stem, so that the electroscope could be used in the open air even in rainy weather." — Encyclopedia Britannica, 1893

Cavallos Electroscope

"Cavallo's electroscope embodies the double pendulum principle. It consists of two fine silver wires…