The phenomenon of thermo-electricity was discovered in 1821 by Thomas Johann Seebeck (1780-1831). In the process of studying the magnetic field set up by an electric current, he constructed a circuit made partly of bismuth and partly of copper. When he held one junction between the two metals in his hand, a current was established, which he attributed to the difference in temperature between the junction in his hand, and the other junction in the circuit. Thus the Seebeck Effect involves the use of temperature differences to produce an EMF, and can be used to detect thermal radiation. The symmetrical Peltier Effect (Jean Charles Athanse Peltier, 1785-1845) uses an electric current to produce temperature differences.

   We rarely mention the Seebeck and Peltier effects to introductory students today, but in the middle part of the century the thermo-electric battery was often used in place of galvanic batteries. Two examples of thermo-electric batteries are shown on this page, both ca. 1900. The circuit consists of a number of copper and bismuth wires, connected in series. All the copper-to- bismuth connections (for example) are gathered together and kept at one temperature, and the bismuth-to-copper junctions were kept at the other temperature. The catalogue of Max Kohl of Chemnitz, Germany, ca. 1900, refers to this as Guelcher's thermolelectric pile, and notes that it is useful for charging batteries.

In both examples, a candle or gas burner is placed in the center of the apparatus to raise the temperature of the junctions collected at that point. The other junctions are kept cooler though the use of radiating fins.     The double thermo-electric battery below was made at Denison University some time before 1885. At the right is a commercial instrument in the collection at Wesleyan University.

This thermoelectric generator is like the one above from Wesleyan, but has five segments instead of three, thus producing a higher output voltage.    Generators of this type were used ca. 1900 to charge storage batteries.    The apparatus is in the collection of Hobart and William Smith Colleges in Geneva, New York.

Here is the basic thermoelectric demonstration. The bottom piece is made of zinc and the top of copper. When one junction is heated, current passes around the loop, setting up a magnetic field and producing a torque on the magnetic needle.    This unmarked piece of apparatus is at Case Western Reserve University in Cleveland, Ohio.