Velocity of Propagation of theHe3 A−BInterface in HypercooledHe3−A

We have measured the velocity of propagation of the ${}_{}{}^3{}_{}{}^{}\mathrm{He} A-B$ interface as a function of temperature and pressure for the ${}_{}{}^3{}_{}{}^{}\mathrm{He}-A$ initially in a hypercooled state. Velocities as high as 67 cm/s have been observed. Nucleation of the $B$ phase occurred at greatly different temperatures in two different regions of the experimental cell.