Lohse's historic plate archive

The description and the analysis of Oswald Lohse's astrophotographic plates , collected at the Astrophysical Observatory Potsdam in the period 1879 - 1 889, are presented. 67 plates of the archive, taken with the greatest instr ument of the observatory at that time - the refractor (D = 0.30m, F = 5.40m , scale = 38 "/mm) and with the second heliographic objective (D = 0.13m, F = 1.36m, scale = 152 "/mm)- survived two world wars in relative good condi tion. The plate emulsions are from different manufacturers in the beginning of astrophotography (Gadicke, Schleussner, Beernaert, etc.). The sizes of the plates are usually 9 x 12 cm(2), which corresponds to fields of 1.2 deg rees and 5 degrees respectively for each instrument mentioned above. The av erage limiting magnitude is 13.0(pg). Besides of the plates received for te chnical experiments (work on photographic processes, testing of new instrum ents and methods of observations), the scientific observations follow progr ams for studies of planet surfaces, bright stars, some double stars, stella r clusters and nebulous objects. Lohse's archive is included into the Wide Field Plate Database (http://www.skyarchive.org) as the oldest systematic o ne, covering the fields of Orion (M42/43), Pleiades, h & chi Persei, M37, M 3, M11, M13, M92, M31, etc. With the PDS 2020 GM(+) microdensitometer of Mu nster University 10 archive plates were digitized.