This is an electroscope based on a principle different from that of the traditional leaf electroscope. The instrument, whose best qualities are high sensitivity and capability to keep the electric charge for a long time, was devised by Macedonio Melloni. The detection of an electric charge is possible thanks to the repulsive interaction of two pairs of thin rods connected to two coaxial cylinders. The conductors are inside a brass cylindrical case covered by a glass plate. The torsion wire holding the inner cylinder goes through a vertical tube inserted into the glass plate. The charge is communicated to a knob connected to the outer cylinder. The whole system rests on three levelling screws. Well-preserved. Overall height 39 cm. Signed: "Ultima scoverta del cavalier Melloni , Saverio Gargiulo, Napoli, 1855".
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