This well known and widely used landmark text explores the universal spontaneous generation of magnetic fields in astronomical bodies and the agitation of the bodies by those fields. The general properties of magnetic fields, their appearance throughout the astronomical universe, and the havoc they wreak are described in simple physical terms so as to define the broad scientific problem presented by magnetic fields.Then, with the physical problems clearly in mind, the theoretical effects are demonstrated with formal mathematical illustrations from the basic electromagnetic equations. The nonscientist with an active interest in astronomy will find extensive material in readable form, while the professional theoretician will find a systematic presentation of the theory.