  Using exact expressions for the Ising form factors, we give a new very simple
proof that the spin-spin and disorder-disorder correlation functions are
governed by the Painlev\'e III non linear differential equation. We also show
that the generating function of the correlation functions of the descendents of
the spin and disorder operators is a $N$-soliton, $N\to\infty$, $\tau$-function
of the sinh-Gordon hierarchy. We discuss a relation of our approach to
isomonodromy deformation problems, as well as further possible generalizations.
