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What did Thomas Johann Seebeck discover about heat and electric current?

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Study how a series of gears in a waterwheel translates a stream's energy to a millstone — energy conversion Before the Industrial Revolution, power came from three main sources: humans, draft animals, and water.
The ingenuity people used in harnessing waterpower can be seen in this medieval-style mill. The waterwheel is turned by a stream and is connected to a shaft that leads into the building. At the other end of the shaft is a gear. The connection of a series of gears translates the power from the stream to a shaft that drives a millstone, which grinds flour from grain.
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In 1821, the German physicist Thomas Johann Seebeck discovered that an electric current is produced in a closed circuit consisting of two dissimilar conductors when their junctions are maintained at different temperatures.12

This phenomenon, now known as the Seebeck effect, occurs because the temperature difference creates a net electromotive force within the circuit. Seebeck observed that this effect occurs with various pairs of metals; for instance, when a copper strip is joined to a bismuth strip, heating one junction induces a continuous flow of electricity as long as the temperature differential persists.132

This discovery is fundamental to the field of thermoelectricity, which involves the direct conversion of heat into electricity. Today, the principle is widely applied in thermocouples for precise temperature measurement and in devices designed to generate electric power for specialized applications.31