  We have carried out an investigation of the abundance of deuterium along two
extended sight lines through the interstellar medium (ISM) of the Galactic
disk. The data include Far Ultraviolet Spectroscopic Explorer (FUSE)
observations of HD 195965 (B1Ib) and HD 191877 (B0V), as well as Space
Telescope Imaging Spectrograph (STIS) observations of HD 195965. The distances
to HD 195965 and HD 191877, derived from spectroscopic parallax, are 794+/-200
pc and 2200+/-550 pc, respectively, making these the longest Galactic disk
sight lines in which deuterium has been investigated with FUSE. The higher
Lyman lines clearly show the presence of deuterium. We use a combination of
curve of growth analyses and line profile fitting to determine the DI abundance
toward each object. We also present column densities for OI and NI toward both
stars, and HI measured from Ly-alpha absorption in the STIS spectrum of HD
195965. The D/H ratios along these sight lines are lower than the average value
found with FUSE for the local interstellar medium (37 to 179 pc from the Sun).
These observations lend support to earlier detections of variation in D/H over
distances greater than a few hundred pc. The D/H and O/H values measured along
these sight lines support the expectation that the ISM is not well mixed on
distances of ~1000 pc.

Astrophysics