The experimental study of magnetospheric processes consists of several disci plines or methods, developing in two general directions. The first, internal trend covers the progress in experimental techniques and methods and re search specific to this discipline. The other trend combines with other methods in a mutual attempt at understanding the boiling whirlpool of the disturbed magnetosphere. Investigations of auroral X-rays began after Van Allen's (1957) discovery of hard radiation in the upper atmosphere of the auroral zone, and are based on high latitude balloon observations. Scientific apparatus, payload equip ment, and particular questions of scientific ballooning are discussed in Chap ter 1. Chapter 2 concludes the internal trend of the subject by describing the problems of X-ray generation at the boundary of the atmosphere and propa gation downward to balloon altitudes. Auroral X-rays are closely related to most of the processes of the disturbed magnetosphere through energetic auroral electrons; precipitating into the at mosphere, the latter create bremsstrahlung photons able to penetrate to an at mospheric depth of 10- 20 g cm - 2. In quiet periods auroral electron flux ex ists only in embryo, as a hot plasma layer at the inner edge of the plasma sheet: in general it is a transient phenomenon caused by magnetospheric distur bances and carrying valuable information of the magnetospheric dynamics.
