  We report on the measurement of the magnetic susceptibility and of ESR
transitions in the garnet substance Tb$_3$Ga$_5$O$_{12}$ (TGG). The results are
compared with a calculation in the framework of crystal field theory for the
orthorhombic surroundings of the six inequivalent Tb ions of TGG. We also
present a calculation of the magnetization for the three main crystal
directions.
