FOOTE AND HARRISON: THERMOELECTRIC EFFECTS 547 



of the latter phenomenon. Some interesting names appear in 

 the hst of early investigators, for example, Becquerel, 1823; 

 Nobili, 1834; Peltier, 1838; Matteuci, 1838; de Heer, 1840; 

 Gaugain, 1862; Coulomb; Righi, 1875; Knott, 1879; Tomlinson, 

 1888; Stroud, 1889; etc. 



Seebeck, 1826, suggested that the emf developed in a single 

 wire on heating asynmietrically was due to a hardening and soft- 

 ening of different portions of the metal. He found that an emf 

 is developed by heating the junction of two similar wires of dif- 

 ferent diameters. Magnus, 1851, after a most thorough inves- 

 tigation, believed the emf developed by touching a hot and a 

 cold wire to be due to a change in hardness produced by heat- 

 ing. Jenkin,"* 1862-3, performed a series of very elaborate ex- 

 periments identical with those described by Benedicks in 1917. 

 Jenkin concluded that the emf obtained by heating crossed 

 wires was due to an oxide film acting w^ith the metal under- 

 neath as an ordinary thermocouple, and that a sufficient tem- 

 perature gradient existed through the film to account for the 

 very large emfs observed. The magnitude of these was em- 

 phasized by the statement "to my surprise it was not until I 

 had added resistance equal to that of 2000 miles of the Red 

 Sea cable, that I reduced the deflections within range of m}^ 

 galvanometer." Jenkin proved that the effect was not chemical 

 or electrolytic. The emf developed by touching hot and cold 

 metal was also explained by x film of oxide. He proved that 

 this latter effect could not be due to static electricity. He 

 recognized that it is questionable to attribute the emfs devel- 

 oped with silver, gold and platinum to surface oxidations and 

 raised the point as to whether the physical property of a metal 

 depends not only upon its temperature but upon the time du'"ing 

 which it has been at this temperature. Jenkin further advo- 

 cated the theory of change in hardening of the two metals 

 placed in contact. 



Durham, 1872, observed that the magnitude of the emf de- 

 veloped on placing hot and cold metal in contact was propor- 

 tional to the original temperature difference of the two metals. 



< Jenkin. British Ass. Rep. 31: 39-41. 1862. Idem. 32: 173-8. 1863. 



