The equilibrium positions of coronal currents are determined. It is shown that the fact that the photosphere has a very large inertia as compared to the corona, poses an important boundary condition at the surface. Electric currents flowing in a coronal active region show a tendency to concentrate above a neutral line. Only here equilibria are possible, determined at low heights by the background field and at large heights by gravity. An instability may occur when the current at low heights exceeds a certain value. The model given is compared with observations of the corona, of prominences, and of fibril motions. Also, the relation with solar flares is discussed in general terms.

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A model for horizontal oscillations of prominences is presented. It is found that the model of a freely oscillating prominence surrounded by coronal matter explains satisfactorily the observed periods and damping times, as well as the changes in the prominence shape.

The temperature structure of the transition region between the chromosphere and corona is discussed in the context of current ideas about magnetic fields in these layers. Magnetic channeling of the downward conductive heat flow from the corona into the regions of enhanced field at the supergranulation boundaries is proposed as a mechanism for explaining the measured intensities of solar ultraviolet emission lines which originate in layers with temperatures below 105 ~ It is shown that nearly all of the observed ultraviolet line emission originates in interspicule regions, and that this emission plays an important part in the energy balance of the cooler layers of the transition region. It is suggested that certain motions observed in the upper chromosphere may represent the earliest visual evidence for conversion of inftowing conduction energy into kinetic motions.