HI spectra and column densities toward HVC and IVC probes

We show 21 cm line profiles in the direction of stars and extragalactic obj ects, lying projected on high- and intermediate-velocity clouds (HVCs and I VCs). About half of these are from new data obtained with the Effelsberg 10 0 m telescope, about a quarter are extracted from the Leiden-Dwingeloo Surv ey (LDS), and the remaining quarter were observed with other single-dish te lescopes. H I column densities were determined for each HVC/IVC. Paper I of this series uses these in combination with optical and ultraviolet high-re solution measurements to derive abundances. Here an analysis is given of th e difference and ratio of N(H I) as observed with a 9' versus a 35' beam. F or HVCs and IVCs the ratio N(H I-9')/N(H I -35') lies in the range 0.2-2.5. For low-velocity gas this ratio ranges from 0.75 to 1.3 (the observed rati o is 0.85-1.4, but it appears that the correction for stray radiation is sl ightly of). The smaller range for the low-velocity gas may be caused by con fusion in the line of sight, so that a low ratio in one component can be co mpensated by a high ratio in another-for 11 low-velocity clouds fitted by o ne component the distribution of ratios has a larger dispersion. Comparison with higher angular resolution data is possible for 16 sight lines. Eight sight lines with H I data at 1'-2' resolution show a range of 0.75-1.25 for N(H I -2')/N(H I -9'), while in eight other sight lines N(H I-Ly alpha)/N( H I -9') ranges from 0.74 to 0.98.