Thermo-electric battery

A professor of applied physics at the Conservatoire, Claude Pouillet, devoted himself to the study of thermo-electric batteries. His battery consists of a metal (bismuth) bar, to each end of which has been soldered a strip of copper. If one of the joins is heated to 100°C while the other is maintained at 0°C, a weak current appears between the strips of copper. Circulating from hot to cold, this current remains constant as long as the temperature difference between the joins does not vary. Pouillet used this battery with a pyrometer to measure high temperatures, and with a pyrheliometer to measure the quantity of heat emitted by the Sun. He used these experiments to verify the application of Ohm’s law (establishing the relationship between an electric current’s intensity and tension) and deduced the law named after him (characterising an electric cell by its electromotive force and internal resistance).