  Entanglement in the ground state of the XY model on the infinite chain can be
measured by the von Neumann entropy of a block of neighboring spins. We study a
double scaling limit: the size of the block is much larger then 1 but much
smaller then the length of the whole chain. In this limit, the entropy of the
block approaches a constant. The limiting entropy is a function of the
anisotropy and of the magnetic field. The entropy reaches minima at product
states and increases boundlessly at phase transitions.
