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Published online by Cambridge University Press: 14 August 2015
Problems of relating different observational indications of the presence of circumstellar matter in binary systems are discussed, with especial reference to the observed period changes in systems whose other properties are very similar. It is suggested that some fluctuations observed in the periods of close binary systems are apparent and not to be attributed to dynamical causes. The discussion includes some account of recent activity in U Cep, and the possible causes of spectroscopic changes in binary systems are examined.