*************************************************************************
   52183
   We propose to determine the gas temperature and heavy element
   abundances for three z~0.3 clusters of galaxies, which will complete
   our survey of eleven high X-ray luminosity distant clusters selected
   from the ROSAT All Sky Survey. With eight clusters in this sample
   exceeding 10^{45} ergs/sec, this sample contains very massive clusters
   whose properties are the most sensitive to the underlying cosmology.
   Thus, comparing the temperature distributions of these distant clusters
   with present epoch high luminosity clusters can constrain cosmological
   models.
 *************************************************************************