Eq. 1 provides a useful description of what is already known, but cannot be used empirically to detect and measure unknown current generators. First, it is rigidly structured, based on the location and intensity of individual generators. Second, the resulting potential is expressed with reference at infinity. Finally, the direction of local current flow in the medium (i.e., orthogonal to the isopotential lines in Fig. 1) is ignored. The end result of these shortcomings is that, even though potential differences can be measured empirically, an unknown generator remains unknown.
