The dominant baryonic component of clusters of galaxies is their X-ray emitting atmosphere. X-ray surveys have made it possible to examine this component in large samples of clusters. Davidet al.(1993) provided a catalog of X-ray temperatures. I have measured 79 clusters from that list using Einstein IPC data (Harriset al.1990), determining several measures of the radius. The most useful turns out to be the Petrosian radius. Given a radius, one can measure the surface brightness at that position.