346 Dr. C. Bams on the Relation between the Thermoelectric 



published (the principal being those of Magnus*, Sir W. 

 Thomson f, and E. Becqucrel %) are of a qualitative nature, 

 the results being derived from the direction of the current 

 observed on bringing together, in one way or another, wires of 

 different hardness. 



The experiments of Magnus being limited to hard-drawn 

 wires, do not properly fall within the scope of the present 

 paper. The same is true of a number of the experiments on 

 steel in the excellent paper of Sir W. Thomson. With regard 

 to the effects of annealing, Prof. Thomson observes: — "In 

 cases of round steel wire, of steel wire flattened through its 

 whole length by hammering, and of steel watch-spring, the 

 thermoelectric effects of annealing portions after the whole 

 had been suddenly cooled was a current from unannealed to 

 annealed through hot." This result comprehends all that has 

 thus far been done. 



(b) Specific Resistance and Hardness of Steel. 



With reference to the specific resistance and hardness of 

 steel, we shall proceed in a manner analogous to the preceding. 

 Denoting the observed specific resistance of a bar by S, that 

 part of S which is due only to the chemical nature of the rod 

 by S , that due to its hardness by AS , we have 



S = S + AS . 



Now, as it follows from results given below that the specific 

 resistance of steel increases continuously with its hardness, it 

 will be convenient to put AS for a soft bar equal to zero. 

 The value of AS for a bar of any degree of hardness thus 

 numerically determined will in the following be accepted as 

 a second measure of that property. 



The work thus far published on the relation between spe- 

 cific resistance and hardness of steel is due principally to 

 Mousson§. Of late results have also been announced by 

 Chwolson || . The data of both observers agree only qualita- 

 tively with mine. 



IV. Determination of Thermoelectric Hardness. Apparatus, 



Method. — In the determination of thermoelectric force the 

 procedure known as Ohm's method was first employed. After- 



* Pogg. Ann. lxxxiii. p. 486, 1851. 

 t Phil. Trans, iii. pp. 709-727, 1856. 

 | Ann. de Chim. et de Phys. [4] viii. p. 402, 1866. 

 § N. Denkschr. d, Schw. Gesellsch. [8] xiv. pp. 1-90, 1855. 

 || Mel. Phys. de St. Petersloury, x. p. 879, 1877. See also Carl's Hepert. 

 xiv. p. 15, 1878. 



