BH Psc=HD 224639: A Delta Scuti star with a rich pulsation spectrum and changing mode amplitudes

New B and V observations of the Delta Scuti star BH Psc (64 hours during 13 quasi-consecutive nights in October and November 1994), combined with the previous ones obtained in 1991, have allowed us to get an improved resolution of its light curve, confirming the presence of a large number (at least 13) of excited modes. There is strong evidence that some modes have large amplitude variations over timescales shorter than a few years, while others seem to be rather stable. There is also evidence that the pulsation energy in 1994 was lower than in 1991. The ratios between the amplitudes of the light and colour curves and their phase shifts, available for the first time, tend to suggest the presence of excited modes with l=2.