Il Duplicatore di Belli del Liceo Classico Parini di Milano

Abstract

The evolution of ideas, in the theoretical and applied domains of Physics, is often marked by the development of specific procedures and devices. The historical collection of physics didactic instruments hosted by Liceo Parini in Milan includes an interesting example from the first half of the nineteenth century. This particular device, known as “Duplicatore di Belli” (Belli’s Doubler), is an electrical machine based on electrostatic induction. Giuseppe Belli, a Physics teacher at the Liceo in the years 1821 – 1840, invented it during his tenure in Milan. Belli educational background is linked to Alessandro Volta and the University of Pavia, where he graduated in 1812 and lately became director of the Physics department. This and other devices he invented can be considered a turning point in the development of electrostatic induction machines, from charge amplifiers to high voltage generators. Investigating this case provides not only a view of the history of the electrical theory in the nineteenth century but also a useful didactical experience for understanding the application of electrostatic induction to electrical device design.