  [Abridged] We present Far Ultraviolet Spectroscopic Explorer (FUSE)
observations of the young, compact planetary nebula (PN) SwSt 1 along the line
of sight to its central star HD 167362. We detect circumstellar absorption
lines from several species against the continuum of the central star. The
physical parameters of the nebula derived from the FUSE data differ
significantly from those found from emission lines. We derive an electron
density n_e = 8800^{+4800}_{-2400} cm^{-3} from the column density ratio of the
excited S III fine structure levels, which is at least a factor of 3 lower than
all prior estimates. The gaseous iron abundance derived from the UV lines is
quite high ([Fe/S] = -0.35+/-0.12), which implies that iron is not
significantly depleted into dust. In contrast, optical and near-infrared
emission lines indicate that Fe is more strongly depleted: [Fe/H] =
-1.64+/-0.24 and [Fe/S] = -1.15+/-0.33. We do not detect nebular H_2
absorption, to a limit N(H_2) < 7\times10^14 cm^{-2}, at least four orders of
magnitude lower than the column density estimated from infrared H_2 emission
lines. Taken together, the lack of H_2 absorption, low n_e, and high gaseous Fe
abundance derived from the FUSE spectrum provide strong evidence that dense
structures (which can shield molecules and dust from the destructive effects of
energetic stellar photons) are not present along the line of sight to the
central star. On the other hand, there is substantial evidence for dust,
molecular material, and dense gas elsewhere in SwSt 1. Therefore, we conclude
that the nebula must have an inhomogeneous structure.
