We propose to map the distribution of the C+ line emission across the
southwest portion of the SMC, in order to study the physical conditions of
interstellar gas with a much lower metallicity than that of typical clouds
in the Milky Way.  Our observations are coordinated with the ongoing
ground-based observations of the molecular gas distribution with the SEST,
and will have resolution comparable to recently completed HI gas maps made
with the ATCA.  Comparison of previous, low-resolution CO and C+
observations of the LMC already indicated that the Magellanic Clouds
present quite different emission lines, with the C+ enhanced relative to CO
by a factor of 18 in comparison with Milky Way clouds.  With similarly
bright lines expected from the SMC, which has even more extreme metallicity
than the LMC, it is possible to map a significant region at 80" resolution
using the ISO LWS.  The region selected contains prominent peaks in the CO
distribution, presumably giant molecular clouds, with some HII regions and
supernova remnants around the edges of the selected region.  The proposed
observations are significantly different from those already planned, which
are complete grating spectra at a small number of positions, because we
will be able to measure the sizes of the emitting regions for comparison
with the recent CO and HI observations.  The emission from the Milky Way
will be separated from that of the SMC in two ways:  by making differential
measurements over the mapped regions, and by explicitly separating the
Milky Way line for select positions using the high spectral resolution
Fabry-Perot.