Critical behaviour of the anisotropic Ising model

The first eleven terms of the high temperature susceptibility series for the anisotropic Ising model on a simple cubic lattice are calculated. The series is analysed to obtain estimates of the critical temperature and critical exponent for various values of the anisotropy parameter eta . Strong evidence is found for an apparent continuous variation of the exponent with eta which is in contradiction with the discontinuous change at eta =0 which has been generally believed to occur. The detailed variation of the critical temperature with eta is also in disagreement with predictions from generalized scaling laws.