|Thermo-electricity: if the ends of two wires, or strips of silver G, and brass B, are put in contact (brazed or soldered together), and the junction heated, a current will flow from the silver to the brass (in the direction of the arrow), if the free extremities of the wires are connected by any conductor of electricity, and thus an electrical circuit will be established. |
The subject of thermo-electricity originated in 1821-1822 when Estonian-born German physicist Thomas Seebeck discovered that a junction of dissimilar metals produces a current when exposed to a temperature gradient, a phenomenon called the thermoelectric effect. The term "thermo-electricity" was used as early as 1834.
At the time of the discovery, aside from natural atmospheric electricity (lightening), four forms of man-made electricity were known:
● Friction under the head first of statical electricity [Guericke's friction generator (1650)] or [Leyden jar (1744)] and electricity from effluent steam, i.e. electricity manifested in an insulated boiler, during the emission of pressurized steam through a narrow aperture [Armstrong (1840)];
● Second of chemical action under galvanism [Galvini's frog legs (1786)] or voltaic electricity [Volta's battery (1800)];
● Third animal electricity;
● Fourth from certain arrangements with magnets, under the head of magneto-electricity [Orsted's electromagnetism (1820)].
The discovery of electricity due to the actions of heat, discovered via experiments made by Seebeck, communicated to the Academy of Berlin in the years 1821 and 1822, was considered as a fifth type
The basic aspects of Seebeck's experiments are explained below: 
|Left: In the first experiment by Seebeck, his apparatus consisted of two different metals (antimony and bismuth were found the most efficient) soldered together at their extremities and formed into frames of either circular or a rectangular figure. He found that electricity was excited by the application of heat to the places at which the metals were united as evidenced by disturbance of the magnetic needle balanced on a point between the two extremities. The best effect is produced by heating one compound corner by a flame and cooling the opposite corner by wrapping it with folds of filter paper moistened with either. Right: In a second experiment by Seebeck, two frames composed of platinum and silver wires are represented delicately poised on the poles of a horseshoe magnet, where it is found that a flame being placed between them causes the circulation of the thermo-electric currents in the wires as evidenced by their rotation around the poles of the magnet.|
In 1834, after receiving a small inheritance from the death of his wife's mother, French physicist Jean Peltier continued the work of Seebeck. In particular, Peltier passed current through a continuous circuit made of two different metals, connected by two different junctions, finding the temperature of one junction to rise and the other to fall. 
In 1838, Russian physicist Heinrich Lenz froze a drop of water using Jean Peltier’s thermoelectric method. 
1. Davis, Daniel, etc. (1842). Davis’s Manual of Magnetism (pg. 21). D. Davis Jr.
2. Kondepudi, Dilip. (2008). Introduction to Modern Thermodynamics (pg. 49). John Wiley & Sons.
3. (a) Noad, Henry M. (1844). Lectures on Electricity (section: 704: Thermo-electricity, pgs. 421-22). K. Knight.
(b) The hydro-electric machine was invented in 1840 by William George Armstrong, after an engine man tending a steam engine received an electric shock when he put one hand on the safety valve of his boiler while his other hand was exposed to a jet of steam.
(c) Armstrong, W.G. (1840). “On the Electricity of Effluent Steam”, Philosophical Magazine (pgs. 452-57), LXVI.
(d) Galvani, Luigi. (1791). De Viribus Electricitatis in Motu Musculari Commentarius (Commentary on the Effect of Electricity on Muscular Motion). Italy.
4. (a) Shachtman, Tom. (1999). Absolute Zero and the Quest for Absolute Cold (pg. 86). New York: Mariner Books.
(b) Jean Peltier – Wikipedia.
5. (a) Shachtman, Tom. (1999). Absolute Zero and the Quest for Absolute Cold (pg. 86). New York: Mariner Books.
(b) Heinrich Lenz – Wikipedia.
● Tait, Peter G. (1884). Heat (ch. XI: Thermo-electricity, pgs. 163-92). MacMillan.
● Thermoelectric effect – Wikipedia.