Change in Velocity of Sound between Normal and Superconducting States in Tin

The difference in the velocity of sound between the normal and superconducting state in tin was measured at 80 kilocycles ${\sec }^{-1\mathrm{}}$. A maximum change of ∼2 parts in ${10}^6$ is found for a longitudinal wave in the [001] direction. Any change in velocity is ${10}^7$ for a longitudinal wave along the [100] direction or a torsional wave along the [001] direction. This disagrees with some previous determinations, but is in accord with other thermodynamic measurements. The effect of strain amplitude and magnetic field on the velocity and attenuation of the sound wave in the normal state has also been investigated in some detail.