Pattern formation in a layer of fluid heated from below is an example of macroscopic ordering in continuous media. Here we show that in a relatively compact experimental version of the problem, a rich and diverse set of stable flows can be found. These flows, many of which are novel, can be categorized and understood in terms of their symmetry properties. This approach shows promise for providing insight into the more complicated fluid motion that occurs as the lateral dimension of the layer is increased.

We describe experiments in which we have observed the onset of Rayleigh-Bénard convection in normal liquid 3He–4He mixtures. Evidence of overstability was seen when heating from below but only stationary convection was observed when heating from above. Measurements of the critical Rayleigh number are presented and compared with the predictions of current theories of marginal stability in a binary mixture. These experiments exemplify liquid 3He–4He mixtures as a system for the study of convective instabilities.

Equipment is described for performing measurements of the Rayleigh–Bénard instability in a sample of rotating liquid 4He. Data are presented on the dependence of the critical Rayleigh number for the onset of convection on Prandtl number in the range 0·49 < Pr < 0·76 and over a range of dimensionless angular velocities 0 < Ω < 200. Evidence for the existence of subcritical convection is presented.

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