This book is a sequel toSTRONG The Enigmatic Photon. Volume 1: The Field/STRONG IX(3)/SUP /EM(Kluwer Academic Publishers, 1994), which presented the first systematic development of the fundamental magnetizing field of electromagnetic radiation: the field £Ii£SUP(3)/SUP. Its 12 chapters collectively describe the properties of IiSUP(3)/SUP in a vacuum and in the interaction of light with matter. BRThe present volume deals with the development of the theory of the Evans--Vigier field IiSUP(3)/SUP. It opens with the derivation of the novel field IiSUP(3)/SUP from the Dirac equation of relativistic quantum field theory. The existence of IiSUP(3)/SUP in the vacuum means that the gauge group of electromagnetism becomes EM0/EM(3), the group of rotations. This is non-Abelian, and so requires a self-consistent development of the vacuum Maxwell equations themselves. The role of IiSUP(3)/SUP is discussed in unified field theory and quantum electrodynamics. The classical vacuum field IiSUP(3)/SUP is a novel, fundamentally important feature of electrodynamics which indicates that the particulate photon carries mass, thus settling a longstanding debate in favour of protagonists of photon mass. BRFor researchers and graduate students interested in the theory of electromagnetic radiation.