A phenomenon discovered in 1834 by J. C. A. Peltier, who found that at the junction of two dissimilar metals carrying a small current the temperature rises or falls, depending upon the direction of the current. Many different pairs of metals were investigated; bismuth and copper were among the first. The temperature rises at a junction where the flow of positive charge is from Cu to Bi and falls where the flow is from Bi to Cu. A reversible output of heat occurs at the first-named junction and a reversible intake at the second. In view of the experiments of Quintus Icilius (1853), which established that the rate of intake or output of heat is proportional to the magnitude of the current, it can be shown that an electromotive force resides at a Cu-Bi junction, directed from Bi to Cu. Electromotive forces of this type are called Peltier emf's.