Review of ultraviolet interstellar extinction and interstellar lines

The limits of optical and radio observations of interstellar gas clouds, H II regions, and dust are reviewed in order to indicate possible applications of UV observations. It is shown how physical parameters of such gas and dust condensates are derived from normal optical observations of interstellar extinction lines and how UV measurements can supplement these observations. Parameters considered include electron density, ionization rates of heavy elements, elemental abundances, temperatures, and cloud densities.