  We present studies of the dc magnetization of thin platelike samples of the
isotropic type II superconductor PbTl(10%), as a function of the angle between
the normal to the sample and the applied magnetic field ${\bf H}$. We determine
the magnetization vector ${\bf M}$ by measuring the components both parallel
and normal to ${\bf H}$ in a SQUID magnetometer, and we further decompose it in
its reversible and irreversible contributions. The behavior of the reversible
magnetization is well understood in terms of minimization of the free energy
taking into account geometrical effects. In the mixed state at low fields, the
dominant effect is the line energy gained by shortening the vortices, thus the
flux lines are almost normal to the sample surface. Due to the geometrical
constrain, the irreversible magnetization ${\bf M}_{irr}$ remains locked to the
sample normal over a wide range of fields and orientations, as already known.
We show that in order to undestand the angle and field dependence of the
modulus of ${\bf M}_{irr}$, which is a measure of the vortex pinning, and to
correctly extract the field dependent critical current density, the knowledge
of the modulus and orientation of the induction field ${\bf B}$ is required.
