Using Maxwell's equations of electrodynamics and the linearized fundamental equation of hydrodynamics neglecting all but the ponderomotive force, the two differential equations characterizing toroidal and poloidal modes of oscillations are obtained. Neglecting the coupling between these modes the toroidal mode which appears to be connected with the phenomenon of geomagnetic micropulsations is studied in detail. Substituting for the constant magnetic field the undeformed dipole field of the Earth the eigenperiods of the oscillating lines of force are computed assuming a constant charge density distribution. Using numerical methods the eigenperiods are also obtained in the case of a variable charge density. Since the Earth's dipole field is presumably deformed by the solar wind a compressed dipole field is introduced into the equation of toroidal oscillations. The eigenperiods of the oscillating lines of force are obtained in this case, assuming a constant charge density distribution. For the case of a variable charge density a numerical method is described which could yield the eigenperiods. / Science, Faculty of / Physics and Astronomy, Department of / Graduate