Thermoelectric Circuit of Three Metals. 



641 



It is well-known that the thermoelectric properties of a 

 metal depend to a marked degree on its purity and on its 

 state of aggregation. The comparison of the constants given 

 in the present paper with those obtained by other observers 

 has therefore no special value. But a rough comparison is 

 not without interest, and the following short table is there- 

 fore appended. The unit of electromotive force for this 

 table is the microvolt. Kohlrausch/ s copper was electrolytic. 

 Tait's copper was probably impure*. Noll's copper was 

 pure. Tait used pare iron, but not Noll ; Tait found that 

 different specimens of iron had thermoelectric properties 

 intermediate between those of pure iron and steel. The 

 numbers giving the results of Kohlrausch and of Noll are 

 from direct observations with the couples mentioned ; those 

 giving Tait's results are derived from Tait's thermoelectric 

 diagram. Noll experimented with both soft and hard wires ; 

 his results would point to slightly higher values for hard than 

 for soft wires in both the cases quoted. 



Couple. 



Copper-Iron. 

 Iron-G.S. 



G.S.-Copper. 

 Copper-Iron. 

 Copper-Steel. 

 G.S.-Copper. 



Copper-Iron. 

 G.S.-Copper. 

 Copper- Iron. 

 Iron-G.S. 

 G.S.-Copper. 

 Copper-Iron. 

 Iron G.S. 

 G.S.-Copper. 



*. 



b . 



+ 10-2 



-030 



-24-1 



-•039 



4-14-6 



+ •058 



4-16-0 



-•058 



4-10-0 



-•042 



4-13-4 



+ •061 



+ 10-5 



-•039 



4-161 



+•036 



4-120 



-•030 



-22-8 



-•009 



4-10-8 



+ •038 



4-11-6 



-•031 



-22-9 



-•010 



4-11-5 



+ •037 



Observer. 

 Kohlrausch. 1 



Tait. 2 " 



Noll. 3 

 Schmitz. 



Remarks. 



Hard-drawn wires (16°-80°) 



Constants for G.S. alter! 



above 150°. 

 Soft wires (0°-182°). 

 „ (0°-216°). 

 Soft wires (0°-80°). 



Hard wires (0 C 



1 Pogg. Ann. vol. cxli. p. 456 (1870), also Pogg. Ann. Erg. vol. vi. p. 35 

 (1874). The above numbers are calculated from those given by Kohlrausch 

 on the assumption that tbe lower temperature in the experiments was 16°. A 

 further reduction of all six numbers by about 3 per cent, is (strictly speaking) 

 necessary to bring them to microvolt-units. 



2 Trans. Roy. Soc. Edin. vol. xxvii. p. 125 (1876), also Everett's ' Units,' 

 ed. 1886. 



3 Wied. Ann. vol. liii. p. 874 (1894). 



In conclusion, it is not without interest to compare the 

 differences between soft and hard wires, as found in the 

 present investigation, with those observed by other experi- 

 menters. In constructing the following short table, the 



* Steele, loc. cit. ; Noll, Wied. Ann. vol. liii. p. 874. 



