Thermo-Electricity at Low Temperatures. VI. A Redetermination of the Absolute Scale of Thermo-Electric Power of Lead
In order to compare the fundamental theory of thermo-electricity at low temperatures with the behaviour of the 'simple' alkali metals (in particular of sodium and potassium) it is essential to have an accurate knowledge of the absolute thermo-electric power of one pure metallic conductor against which the measurements can be made. We have accordingly determined the absolute thermo-electric power of zone-purified lead up to 18 degrees K by direct measurements against the superconductor Nb3Sn. The new measurements, because of the high superconducting transition temperature of Nb3Sn, leave only the very small region between 18 and 20 degrees K in which the Thomson heat of lead must be interpolated to join the values obtained by Borelius and co-workers in earlier work, in order to extend the new scale of absolute thermo-electric power of lead up to room temperature. The variation of the Thomson heat of lead as a function of temperature below 20 degrees K appears to be of some intrinsic interest.