THERMO-ELECTRIC QUALITY UNDER PRESSURE. 



367 



as it is for the majority of metals, and is exceeded in value only by 

 bismuth and thallium. The wire was seasont^d for the pressure runs 

 on thermal e.m.f. by raising pressure to 11300 kg. at room tempera- 

 ture, then raising temperature to 100° for 2| hours, the pressure 

 rising to 11500. Large permanent zero readings might be expected 

 with this substance, because its thermal e.m.f. against iron is so high, 

 but its homogeneity was so great that the zero effect was only about 

 5% of the pressure effect at any temperature. A curious effect was 



Temperature 



Constantan 



60° 

 Temperature 



iifflo i 



80° 100°^ 



Figure 43. Constantan. On the left, the heat absorbed by unit quantity 



of electricity in flowing: from uncompressed metal to metal compressed to the 



pressure indicated on the curves, as a function of temperature. On the right, 



the excess of Thomson heat in metal compressed to the pressure indicated on 



■ the curves over uncompressed metal, as a function of temperature. 



observed immediately after changes of pressure, before temperature 

 equilibrium was reached; there were violent oscillations of e.m.f., 

 changing sign with a period of a few seconds, which gradually dis- 

 appeared. This is possibly an effect of shifting internal equilibrium 

 connected with the complicated nature of the alloy, but is more prob- 

 ably a pure temperature effect, and is particularly prominent here 

 because of the unusually large e.m.f. between constantan and the 

 steel of the cylinders. The immediate effect after a change of pres- 



