The creation of an electrical potential across points in a metal that are at different temperatures. The effect is caused by the thermal energy of the valence electrons in the warmer part of the metal; the kinetic energy of these electrons, which are very free in metals, allows them to migrate toward the colder part more readily than the colder electrons migrate to the warmer part. The colder part of the metal is therefore more negatively charged than the warmer part, resulting in electric potential. The Seebeck effect is used in thermocouples. It was discovered by the German physicist Thomas Seebeck (1770-1831).