First Optical Results on an X-Ray Selected Sample of ROSAT Clusters of Galaxies Pierre, M. ; Schuecker, P. ; Böhringer, H. ; Cruddace, R. ; Ebeling, H. ; Voges, W. ; Collins, C. ; MacGillivray, H. ; Romer, A. Abstract Publication: Observational Cosmology Pub Date: January 1993 Bibcode: 1993ASPC...51..361P