New Measurements of Wetting by Helium Mixtures

We have measured the contact angle of the ³He–⁴He interface on a sapphire window in the temperature range from 50 to 845 mK. Contrary to what had been found by Ueno et al. in two successive experiments, we have found complete wetting by the ⁴He-rich phase. Our new results have two consequences: first, we suspect that there were some artefacts in the experiments by Ueno et al. Secondly, we now believe that the critical Casimir forces are dominated by the van der Waals force in this experimental situation.