For the past six years astronomers have been regarding the universe through a new window—the X-ray window. In these six years this subject has experienced a ‘remarkable’ growth. In late 1966 workers from the Naval Research Laboratory (NRL) published a catalogue containing 35 X-ray sources. In my preparation for this report I have compiled a new catalogue containing only 22 sources (which I believe contains all of the presently confirmed X-ray sources). This early proliferation of ‘sources’ may be attributed to the exuberance of the experimenters or perhaps to a poor understanding of the laws of statistics. A simple calculation shows that, with this rate of decrease of ‘observable’ sources, X-ray astronomy will cease to exist as a subject in 1972!