  We have studied the anisotropy of the London penetration depth, which was
obtained from reversible magnetization measurements with the magnetic field
both parallel and perpendicular to the c-axis. The anisotropy of the London
penetration depth has a smaller magnitude than the anisotropy of the upper
critical field and increases with temperature while that of the upper critical
field decreases as reported earlier. This behavior is in sharp contrast with
the behaviors of superconductors with one superconducting energy gap. The
temperature dependence of the anisotropies of the London penetration depth and
of the upper critical field can be well explained within the theory of two-gap
superconductivity in MgB2.
