Thermocouples

Seebeck was experimenting with circuits made of two different metals—like copper and iron. He noticed that when he heated one end of where the metals joined, a nearby compass needle would deflect. He had accidentally discovered the : a temperature difference between two dissimilar metals creates a tiny flow of electricity, or voltage. How the "Story" Works Every Day A Closer Look at Thermocouples - WARE Boiler

The story of the is one of invisible energy and accidental discovery, beginning in 1821 with a physicist named Thomas Johann Seebeck . The Accidental Spark thermocouples