[en] The lower hybrid slow wave tends to follow magnetic field lines. Therefore, a generalization of Snell's Law modifies the wave length along the magnetic field as the wave moves inward from an exciter through regions of varying magnetic field strength. Predicting the consequences requires a numerical treatment, which has been developed in recent years by several authors. This paper searches for some general statements on the problem by analyzing many particular cases, without allowing for scattering, multiple traverses of the plasma radius, and non-linear effects. We find that the range of parameter suitable for ion heating varies from that predicted by simple estimates, and is dependent on launch position; and that electron heating including current drive is best pursued with unidirectional launching from a coupler at the top (or bottom) of the torus if the wave frequency is close to linear mode conversion condition