It is composed of a wooden column painted red (height 21 cm) on a round wooden pedestal painted black. to which are attached two small hinged arms holding two glass insulating rods (13 cm long). At the end of each rod there is a silk thread at the bottom of which there is a ball made of elder pith which, being attracted by charged bodies, is used to establish whether a body is charged or not. The ball, once it has been charged by contact, is attracted by the bodies with a charge opposite to its charge and repulsed by bodies having the same charge; it can thus also be used to determine the charge of electrified bodies.
Other experiments can be performed by charging the two balls with opposite charges or by charging one and leaving the other uncharged.

Daguin (1878), T III, p. 102
Drion - Fernet (1883), p. 359
Ganot (1864), p. 502

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