A series of laboratory experiments have been carried out which demonstrate the conditions favourable for vacillation in baroclinic thermally driven flows in a rotating annular convection chamber. As earlier studies have indicated amplitude vacillation occurs close to the transitions between dominant wave numbers in the regime under which regular waves are observed. Amplitude vacillation is shown to be less common when the depth of the system is decreased; it is not greatly affected by the use of a free or rigid upper boundary condition. It is however much more frequent when the Prandtl number of the convecting fluid is increased from 11 to 74 although in these experiments other parameters of the system, eg the isotherm slopes, were necessarily changed. Shape vacillation is only significant in the experiments when the upper surface is free; it is not influenced by the nature of the fluid.
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