An almost Complete Survey of 21 Centimeter Line Radiation for |b| Greater than or Equal to 10 Degrees .III. the Interdependence of H i, Galaxy Counts, Reddening, and Galactic Latitude

We compare three extinction indicators: the Shane-Wirtanen galaxy counts (NGAL), H I column density (NHyD), and reddening. There is no simple relation between any pair of these three indicators. Each indicator depends on galactic latitude as well as on the other indicator. With reddening considered as the independent variable this latitude dependence occurs for both galactic and extragalactic objects. The H I to extinction ratio varies by a factor of about 2 from one region to another. We must regard all extinctions presently stated for extragalactic objects as uncertain by a few tenths of a magnitude. Previous analyses of the galaxy counts have led to values of the longitude-averaged extinction which are approximately twice as large as obtained by using other methods. We empirically show that d log NGAL/dApg is about twice as large as the theoretical value, which reconciles the discrepancy. A linear dependence of log NGAL upon csc Ibis found for hI > 60o. The slope of this is about the same as for IbI < 600, suggesting that dust is present at high latitudes. Subject headings: galaxies: structure - interstellar: matter - radio sources: 21 cm radiation