Onset of Rayleigh-Bénard convection in binary liquid mixtures of ³He in ⁴He

We describe experiments in which we have observed the onset of Rayleigh-Bénard convection in normal liquid 3 He– 4 He 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 3 He– 4 He mixtures as a system for the study of convective instabilities.