On the nature of the B-(3) field

It is shown that the Maxwell-Heaviside theory is incomplete and limited, fo r example, it is unable to describe the Sagnac effect, either with platform at rest or in motion. An electrodynamical theory based on a physical inter nal O(3) gauge space is shown to provide the correct explanation in classic al electrodynamics for the Sagnac effect, and for interferometry in general , for example Sagnac and Michelson interferometry. The U(1) sector of unifi ed field theory must therefore be replaced by an SU(2) sector broken to O(3 ). This has numerous consequences for unified field theory.