The effects of large-scale convection currents and differential angular velocity on the Sun's general magnetic field are studied in detail, with the following results :— (i) Cowling's theorem (1) on the dynamo action of convection currents is extended to the case where a small external magnetic field is produced in the convection currents themselves. It is shown that a general magnification of the external field would only be possible if the Hall current were sufficiently large. In the Sun the field so produced would be negligible. (ii) Ferraro's work (2) on the effect of differential angular velocity on the field is extended to allow for the Hall effect. It is confirmed that the observed differential angular velocity is incompatible with the existence of a steady general magnetic field in the solar atmosphere. (iii) The concept of transverse conductivity must be used with caution owing to the action of the mechanical force of the resulting magnetic field in setting the gas in motion.