548 FOOTE AND HARRISON: THERMOELECTRIC EFFECTS 



Trouton, 1886, considered the emf developed by moving a 

 flame along a homogeneous wire. From an interesting experi- 

 ment he concluded that the emf is a function of 8W/8x8t i.e., 

 of the rate of change of the temperature gradient along the wire, 

 and that an emf galvanometrically measurable could not be de- 

 veloped by a temperature gradient alone however asymmetrical. 

 He suggests that the effect is due to either a permanent altera- 

 tion in the wire, or, with some metals, to a temporary altera- 

 tion which lags behind the temperature change. In this he con- 

 firms the opinion of Jenkin. 



Steel, ^ 1893, under the title ''A new thermoelectric phenome- 

 non" describes several of the above mentioned effects, while 

 Turnbull,'' 1894, calls attention to the fact that these effects 

 have been known for years. Turnbull suggests that the emfs 

 are due to strain, an explanation given by LeRoux, 1867, and 

 others. 



Backhmetieff and Stambolieff,^ 1895, heated a homogeneous 

 wire by an electric current. The heating current was then cut 

 off and the two ends of the wire were connected to a galvan- 

 ometer w^hile the wire cooled. "The direction of the current 

 was almost without exception opposite to the direction of the 

 original heating current. "(!) 



An interesting discussion appeared in the German technical 

 journal Elektro Teknische Zeitschrift 1900-4. Egg-Sieberg ''dis- 

 covered" that emfs were developed on heating an iron wire by a 

 moving flame, on touching hot to cold iron, and on heating an 

 iron" wire dipping into water — thus causing an asymmetrical 

 temperature gradient. He concluded that since the Thomson 

 effect was established it was quite reasonable to assume that 

 this depended upon the steepness of the temperature gradient. 

 Hence in a homogeneous circuit having an asymmetrical tem- 

 perature gradient, a measurable emf is developed on account of 

 the gradient coefficient of the Thomson effect. 



5 Steel. Science, 22: 256. 1893. 



« Turnbull. Science, 23: 91-2. 1894. 



' Journ. Russ. Phys. Chem. Soc. 27: 1-25. 1895. 



