Tests for models of high-velocity cloud systems

All models of the system of high velocity clouds (HVCs) seen in 21 cm emission of our Galaxy make fairly clear predictions as to the locations of the clouds and their abundances. Less well documented are predictions as to the H alpha emission properties and the presence, in absorption, of ions such as C IV. I discuss techniques for obtaining distances of the clouds, using the presence of interstellar absorption in RR Lyrae stars and globular clusters, and for obtaining abundances, both absolute and relative. The lack of progress in application of these straightforward techniques is mainly due to lack of proper instrumentation that allows step by step progress with modest exposure times.