In 1821 the German scientist Thomas Seebeck (1770-1831) was experimenting with the thermal properties of certain metals. He constructed a loop of two different metals and applied heat to one of them. To his surprise a magnetic field was formed, as if a current had been generated between the two metals. This phenomenon was named the Seebeck effect, even though Seebeck himself did not fully understand it.

Nearly a century later Seebeck's work became the basis for the field of thermoelectricity, and his metal loop was recognized as the first thermocouple. The Seebeck effect can be observed when an electric circuit is formed from wires of two different metals and the two ends are at different temperatures. A simple galvanometer will then detect the voltage difference between the two metal ends, and the temperature of one end can be determined if the temperature of the other is known. This...