The nature of the B(3) field

Abstract The nature of the B (3) field is determined through deductions from its mathematical definition; B (3) is a vector function of the magnetic field of electromagnetic radiation. The sign and magnitude of B (3) measure the polarization of the radiation, and it is re-normalized to define the Polarization Index (a dimensionless number of magnitude unity), which proves to be identical with one of Stokes's parameters. This is revealed to be the essential nature of the B (3) field. The definition of B (3) (and of the Polarization Index) is generalized in terms of all components of the electromagnetic field rather than only the transverse magnetic components. The analysis leads to internal inconsistencies if the B (3) field is presumed to be the longitudinal component of the physical magnetic field of electromagnetic radiation as asserted by M.W. Evans (the originator of the theory of the B (3) field). This inference explains the failure of experimental investigations to detect the hypothetical longitudinal magnetic field of radiation. It also corroborates a disproof by counter-example by E. Comay.