  For decades, perhaps even centuries, the exchange of publications between
observatories was the most important source of information on new astronomical
results, either in the form of observational data or new scientific theories.
In particular, small observatories or institutions used this method. The
exchange of physical material between observatories has now been replaced by
the exchange of information via the Internet. Yet much of the ancient material
has never been digitized and can only be found in the few existing collections
of observatory publications. A recent donation of such a collection from the
University of Copenhagen to our own library at the University of Southern
Denmark has led us to investigate the uniqueness of such collections: Which
observatories and publications are represented in the collections that still
exist today? We also examine the availability of the material in the
collections.
