  We show that in the new description, Dirac's ``current vector'' is not
related to a vector but to a tensor: the ``stress-energy tensor.''
Corresponding to Dirac's conservation law, we have the conservation laws of
momentum and energy. The stress-energy tensor consists of two parts: an
``electromagnetic'' part, which has the same structure as the stress-energy
tensor of the Maxwell theory, and a ``mechanical'' part, as suggested by
hydrodynamics. The connection between these two tensors, which appears
organically here, eliminates the well-known contradictions inherent in the
dynamics of electron theory. (Editorial note: In this paper Lanczos continues
to discuss his ``fundamental equation,'' from which he consistently derives
Proca's equation and its stress-energy tensor.)
