  We carry out an analysis of the effect of a quenched magnetic field on the
dynamics of the spherical Sherrington-Kirkpatrick spin-glass model. We show
that there is a characteristic time introduced by the presence of the field.
Firstly, for times sufficiently small the dynamic scenario of the zero field
case - with aging effects - is reproduced. Secondly, for times larger than the
characteristic time one sees equilibrium dynamics. This dynamical behaviour is
reconciled with the geometry of the energy landscape of the model. We compare
this behaviour with experimental observations at a finite applied field.
