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   PR # 42178
   We propose to study a ``complete'' set of distant ($z\approx
   0.3-0.4$) luminous ($L_x \approx 10^{45}$ ergs s$^{-1}$ or greater)
   clusters which complements the generally less luminous sample of EMSS
   clusters at $z\approx 0.3$ observed with ASCA. The proposed clusters
   represent the extreme upper end of the cluster luminosity function
   and will probe the nature of the negative evolution reported for the
   cluster X-ray luminosity function. We propose to measure the
   temperature and heavy element abundance in the intracluster medium
   for a comparison with the most luminous present epoch clusters. With
   8 clusters we can make a meaningful initial comparison of the
   properties of present epoch and distant clusters and compute a high
   redshift cluster temperature distribution function.
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