Composition of Interstellar Clouds in the Disk and Halo. IV. HD 215733

In this paper we continue our investigation of diffuse clouds in the interstellar medium with an analysis of the line of sight towards the star HD 215733, located in the Galactic halo some 1700 pc below the plane. As in our previous papers, we utilize the component fitting technique to determine velocities, velocity widths, and column densities for a variety of ions in each of the absorbing regions detected. Our data include a large number of ultraviolet absorption lines observed with the Goddard High Resolution Spectrograph and ground-based observations of Ca II K absorption and H I 21-cm emission. We detect 23 components (absorbing regions) in the low-ionization species towards HD 215733 and 7 components in the highly ionized species (i.e., Si 3+ , C 3+ , and N 4+ ). The low ion components are predominantly neutral. Gas-phase abundances measured for these components follow the pattern seen for halo stars in our previous studies. These have been interpreted as indicating either ...