The Leyden jar owes its name to the place where Peter von Musschenbroek, professor of experimental physics at the University of Leyden, accidentally discovered the "extraordinary" effects of this curious instrument. It was 1745 and, according to the electrical theories commonly accepted at the time, the phenomena of attraction and electrostatic repulsion were due to the motion of an electric fluid that could be transported from metals and aqueous solutions and accumulated and stored in glass containers. It was enough to put a metal rod inside a bottle full of water because electricity will enter, however, paying attention to place the bottle on an insulating material to prevent the electric fluid slip away, through a conductor, towards the earth. When Musschenbroek, contrary to distraction to this experimental rule, filled the bottle holding it in his hand, he was overcome by the feeling that he felt in touch with the other hand the bottle knob. The intensity of the shock caused him to make public the results of its accidental discovery and, from that moment, physicists from across Europe rushed to repeat the experiment. Allowing to accumulate large amounts of electricity, the Leyden jar became a key instrument of "electrical science", it is used to produce large sparks which to deliver strong shocks for therapeutic purposes.