Art. Y. — A New Themioelectnc Phenojnenon. 

 (With Plate VII.) 



By W. HuEY Steele, M.A. 



[Read 13th April, 1893.] 



In text books on thermoelectricity it is u.sually stated that 

 while an electromotive force may be caused by heating part of 

 some metal, which either in its molecular condition, or in its .shape, 

 is not homogeneous or symmetrical, no electromotive force can 

 be caused by heating a homogeneous piece. The experiments of 

 Magnus in his paper on Thermoelectric Currents in Fogg. Ami., 

 1851, are generally quoted as authority, but the experiments 

 described below (performed in the Physical Laboratory of the 

 University of Melbourne) seem to show that these statements 

 require to be greatly modified. Magnus, using a very sensitive 

 galvanometer, obtained a number of relative measurements of the 

 electromotive force produced when similar wires at different 

 temperatures were brought into contact, and when wires of the 

 same materia] but different temper were heated in contact. But 

 he got no effect from heating a single wire up to 100° C. But it 

 appears that he had td take great precautions to prevent unequal 

 heating or temper, or an e.m.f. was sure to appear. An 

 important and interesting example of ati electromotive force 

 from one metal is described by Mr. F. T. Trouton ( Proc. Roy. 

 Soc, 1886), where it is generated by moving a flame along a steel 

 or iron wire slowly enough to make it red hot. The e.m.f., he 

 says, is generated between the part which has cooled through the 

 critical point and the part which is coming to it. This is of 

 varying magnitude. In a recent report of a committee of the 

 British Association to inquire into the phenomena connected with 

 iron at a dull red heat it is stated that on bringing together a 

 bright red iron wire and a cold one, an electromotive force of -Oi) 

 volt is generated. Both of these phenomena, but especially 

 Trouton's, probably depend on the great change in the magnetic 

 susceptibility of iron at a dull red heat. 



