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Published online by Cambridge University Press: 03 August 2017
The existing data on proper motions from meridian catalogues and proper motion surveys appear to be reasonably complete for motions larger than 0.24 arc seconds per year and down to the 19th magnitude visual but for motions between 0.24 and 0.18 there exists a lacuna for stars between 8.5 and 11.5 visual which could easily be observed by repeating Carte du Ciel plates.