The Role of the Critical Ionization Velocity Effect in Interstellar
  Space and the Derived Abundance of Helium
  Gaussian analysis of new, high-angular-resolution interstellar 21-cm neutral
hydrogen emission profile structure more clearly reveals the presence of the
previously reported signature of the critical ionization velocity ({\it CIV})
of Helium (34 km s$^{-1}$). The present analysis includes 1496 component line
widths for 178 neutral hydrogen profiles in two areas of sky at galactic
latitudes around $-$50$^\circ$, well away from the galactic plane. The new data
considered here allow the interstellar abundance of Helium to be calculated,
and the derived value of 0.095 $\pm$ 0.020 compares extremely well with the
value of 0.085 for the cosmic abundance based on solar data. Although the
precise mechanisms that give rise to the {\it CIV} effect in interstellar space
are not yet understood, our results may provide additional motivation for
further theoretical study of how the mechanism operates.
