  Dense distributions of string-like objects in material media are considered
in terms of continuum field theory. The strings are assumed to carry a
quantized abelian topological charge, such as the Burgers vector of
dislocations in solids or magnetic flux of supercurrent vortices in type-II
supercondoctors. Within this common framework the facts known from dislocation
theory can be extended, in appropriately modified forms, to other physical
contexts. In particular, the concept of incompatible distortions is
transplanted into the theory of type-II superconductivity. The compatibility
law for type-II superconductors is derived in terms of differential forms. As a
result, one obtains an appropriate generalization of the classic Londons'
equation.
