FOOTE AND HARRISON: THERMOELECTRIC EFFECTS 549 



Schneider, 1904, repeated the above experiments and con- 

 chided that the effect was due to oxide. This conclusion was 

 undoubtedly correct, especially in connection with his own work, 

 as the resistance of the wires used increased during heating from 

 2 ohms to 100,000 ohms, and emfs amounting to a half volt 

 were observed. 



Hirschson, 1904, suggested that the above effect was due 

 both to the thermoelectric action of the oxide and metal and to 

 the fact that the oxide acted as a shunt on the iron to which it 

 adhered. He showed that the measured potential difference 

 may be in either direction depending upon the extent of the 

 oxidation. 



Rosing^ investigated the emfs developed by touching hot 

 and cold metals. He observed no emf for lead. For gold, silver, 

 copper, u'on, tin and platinum the current flows in one direction, 

 in the reversed direction for palladium and German silver, and in 

 either direction for aluminum depending upon the temperature. 

 He relates the effects for these metals to the thermoelectric 

 power relative to lead. The metals of the first group have a 

 positive thermoelectric power, while those of the second group 

 have a negative thermoelectric power. The thermoelectric power 

 of aluminum is either positive or negative depending upon the 

 temperature. 



The only new suggestion which the writers are able to add to 

 the confusion already existing is that the sign of the emfs de- 

 veloped upon touching hot and cold m.etal appears to have some 

 relation to the sign of the Thomson effect. 



The object of the present note has been two-fold. First, to 

 call attention to the fact that the existence of many of these 

 curious thermoelectric forces, ''rediscovered" every decade, has 

 been well recognized for over a century, and secondly, to point 

 out that no conclusive evidence for their cause has been ad- 

 vanced although nearly all conceivable causes have at times 

 been suggested. 



8 Rosing. Journ. Russ. Phys. Chem. Soc. 30: 151. 1898. 



