Absorption of 10‐Mc Sound in Polycrystalline Superconducting Indium Free

The results of measurements on the absorption of 10‐Mc sound in rods of polycrystalline, superconducting indium will be described. Although the absolute absorption coefficient has not been measured, the dependence of a related quantity, the transmitted pulse height, on temperature has been determined for two samples of indium of different purity. The temperature range covered extends from approximately 4.2°A to 1.5°A. Generally, the temperature dependence of transmitted pulse height in superconducting indium resembles that in superconducting tin [L. Mackinnon, Phys. Rev. 98, 1181 (A) 1955], but with the less pure sample, at least, the relative variation over the temperature range covered is not as large as with tin. [Work supported in part by the Office of Naval Research.]