On the period history of chi Cygni

We discuss the light Variability of the Mira variable chi Cygni, present a homogeneous set of times of minimum and maximum light since its discovery d ate in 1686, and analyse the variations of the pulsation period. There is a substantial cycle-to-cycle variation in the pulsations (standard error sim ilar to 6.(d)5) with quite strong evidence for a linearly increasing period . Quasicyclic patterns in the O - C diagrams are visible, but there is no c ompelling evidence that these apparent cyclic period changes are real since the residuals left after fitting a linear period increase plus intrinsic p eriod scatter have properties consistent with being white noise. The Lombar d frequency domain test for a changing period applied to the residuals also gives unconvincing significance levels. The low gradient of the luminosity change with period is compatible with the star undergoing a rise in lumino sity when H shell-burning takes over.