  Spectra of about 150 early-type stars in the disk of the Milky Way recorded
by the Far Ultraviolet Spectroscopic Explorer (FUSE) reveal absorption features
from interstellar O VI, a tracer of collisionally ionized gases at temperatures
near 300,000 K. (Hotter material is better sensed by its diffuse x-ray
emission.) The FUSE survey indicates that hot gas in the plane of the Galaxy
yields an average density n(O VI) = 1.7 X 10^{-8} cm^{-3}, a value consistent
with earlier results from the Copernicus satellite, but at great distances
there is a large dispersion in the measurements from one line of sight to
another. This dispersion indicates that O VI absorbing regions probably have a
broad distribution of sizes, perhaps giving a power-law behavior for column
densities. Comparisons of O VI with other Li-like ions should give some
guidance on the nature and origin of the O VI-absorbing regions, but poor
correspondences in the velocity profile shapes will complicate the
interpretations.
