Boston Museum of Science electrostatic display operator, Don Salvatore, demonstrates the safety of a Faraday cage as he is protected from a 2.5-million-volt Van de Graaff static electricity generator. A Faraday cage is an earthed screen made of metal wire that surrounds an electric device in order to shield it from external electrical fields. Artificial lightning passes through the metal frame. Physicist Robert J. Van de Graaff invented this model in 1931. MODEL RELEASED (1992).