  The helicity modulus for a fluctuating type II superconductor is computed
within the elastic medium approximation, as a probe of superconducting phase
coherence and the Meissner effect in the mixed state. We argue that at the
vortex line lattice melting transition, there remains superconducting coherence
parallel to the applied magnetic field, provided the vortex line liquid retains
a finite shear modulus at finite wavevector.
