The Collaborative International Dictionary of English v.0.48:

Thermocurrent \Ther"mo*cur`rent\, n. [Thermo- + current.]
   (Physics)
   A current developed or set in motion by heat; specif., an
   electric current, in a heterogeneous circuit, due to
   differences of temperature between the junctions of the
   substances of which the circuit is composed.
   [Webster 1913 Suppl.]