1.    Laws of Successive Contacts or Intermediate Metals: The insertion of a new metal into a circuit of a thermo-couple does not alter the existing e.m.f. provided that the entire added metal is at the same temperature as the point at which it is inserted.

If the metals A, B and C be joined to form a complete circuit, then we shall have



2.    Laws of Successive Eemperatures or Intermediate Temperatures: The e.m.f. of a thermo-couple having junctions at temperatures T₁, and T₂ is the sum of e.m.f. of two separate thermo-couples of the same metals such that the junctions of one are at emperatures T₁ and T₂ and of other at T₂ and T₃.

Mathematically  

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