The Peltier coefficient may also be expressed in volts or microvolts, and may be regarded as the measure of an E.M.F.
The value found at a temperature of 150° C. was +2.5 microjoules per ampere-second per degree, or +2.5 microvolts per degree in the case of copper, which agrees very fairly with the value deduced from thermoelectric tests.
The value found by Batelli for iron was - 5 -o microvolts per degree at 108° C., which appears too small in comparison.
Taking the lead-iron couple as an example, the value of dE/dt at the hot junction too° C. is 10.305 microvolts per degree, and the value of the Peltier coefficient P = TdE/dT is +3844 microvolts.
If the circuit is open, as represented in the diagram, the flow will cease as soon as it has raised the potential of the iron 3844 microvolts above that of the lead.