290 Prof. Thomson on the Dynamical Theory of Heat. 



electric current must produce different effects according as it* 

 passes from hot to cold, or from cold to hot, in an unequally 

 heated metal, was taken as an example in my first communication 

 of the theory to this Society*; and the two metals, copper and 

 iron, were made the subjects of a consequent experimental inves- 

 tigation, to ascertain the quality of the anticipated property in 

 each of them separately. The application of the general rea- 

 soning to this particular case, and the answers which I have 

 derived by experiment to the question which it raises, are de- 

 scribed (§§ 122-133) in a Keport communicated to the Royal 

 Society of London, March 31, and contained in the ' Proceedings' 

 published in this Magazine for July 1854. 



§§ 134, 135. Inserted September 15, 1854. 



134. A continuation of the experiments has shown many 

 remarkable variations of order in the thermo-electric series. 

 The following Table exhibits the results of observations to deter- 

 mine neutral points for different pairs of metals ; the number at 

 the head of each column being the temperature Centigrade at 

 which the two metals written below it are thermo-electrically 

 neutral to one another; and the lower metal in each column 

 being that which passes the other from bismuth towards antimony 

 as the temperature rises. 



I also found that brass becomes neutral to copper, and copper 

 becomes neutral to silver, at some high temperatures, estimated 

 at from 800° to 1400° Cent, in the former case, and from 700^ 

 to 1000° in the latter, being a little below the melting-point of 

 silver. The following diagram exhibits the results graphically, 

 constructed on the principle of drawing a line through the letters 

 corresponding to any one of the metallic specimens in a table 

 such as that of § ISOf, and arranging the spaces so that each 

 line shall be as nearly straight as possible, if not exactly so. 



* See Proceedin<2;s of the Royal Society of Edinburgh, Dec. 15, 1851 ; 

 or Phil. Mag. vol. iii. p. 529, 1852. 

 t Phil. Mag. for July 1854, p. 6/. 



