  We consider barotropic motions described by the compressible Navier-Stokes
equations in a box with periodic boundary conditions. We are looking for
density $\varrho$ in the form $\varrho=a+\eta$, where $a$ is a constant and
$\eta|_{t=0}$ is sufficiently small in $H^2$-norm. We assume existence of
potentials $\varphi$ and $\psi$ such that $v=\nabla\varphi+\mathrm{rot}\psi$.
Next we assume that $\nabla\varphi|_{t=0}$ is sufficiently small in $H^2$-norm
too. Finally, we assume that the second viscosity coefficient $\nu$ is
sufficiently large. Then we prove long time existence of solutions such that
$v\in L_\infty(0,T;H^2(\Omega))\cap L_2(0,T;H^3(\Omega))$, $v_{,t}\in
L_\infty(0,T;H^1(\Omega))\cap L_2(0,T;H^2(\Omega))$, where the existence time
$T$ is proportional to $\nu$. Next for $T$ sufficiently large we obtain that
$v(T)$ is correspondingly small so global existence is proved using the methods
appropriate for problems with small data.
