**2. Method**

### **2.1. Description of a physical circuit describing two parallel conductors**

A geometry is defined, with two parallel conductors aligned to the x axis in a Cartesian coordinate system. They are assumed to be of a length that is very long compared to the rectilinear distance. Already Maxwell complained that this kind of analysis is incomplete, if not taking into account the track along which the respective currents returns to its origin and that the apparent conflict between the theory of Ampère and that of Grassmann is related to this [19]. This is done here, too.

**Figure 1.** The configuration according to Ampère's bridge used in order to realize a "two-infinite-parallel-conductor" circuit
