  We study the Mott transition as a function of interaction strength in the
half-filled Hubbard chain with next-nearest-neighbor hopping t' by calculating
the response to an external electric field using the Density Matrix
Renormalization Group. The electric susceptibility chi diverges when
approaching the critical point from the insulating side. We show that the
correlation length xi characterizing this transition is directly proportional
to fluctuations of the polarization and that chi ~ xi^2. The critical behavior
shows that the transition is infinite-order for all t', whether or not a spin
gap is present, and that hyperscaling holds.
