A magnet assembly comprising first and second sets of coils (1, 2) for
generating respective magnetic fields, wherein the coils are constructed
and arranged such that under working conditions, a first homogeneous
region (3) can be generated within the envelope defined by the magnet 10
assembly and a second homogeneous region (4) can be generated outside the
envelope, the resultant magnetic field in each region being sufficiently
homogeneous to enable a NMR process to be performed on an object in the
region.